Advertisement

Influence of oral vitamin and mineral supplementation on male infertility: a meta-analysis and systematic review

  • Author Footnotes
    † These authors contributed equally to this work.
    Kai Buhling
    Correspondence
    Corresponding author.
    Footnotes
    † These authors contributed equally to this work.
    Affiliations
    Department of Gynecology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
    Search for articles by this author
  • Author Footnotes
    † These authors contributed equally to this work.
    Annika Schumacher
    Footnotes
    † These authors contributed equally to this work.
    Affiliations
    Department of Gynecology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
    Search for articles by this author
  • Christine zu Eulenburg
    Affiliations
    Department for Medical Biometry and Epidemiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

    Present address: Department for Epidemiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
    Search for articles by this author
  • Elena Laakmann
    Affiliations
    Department of Gynecology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
    Search for articles by this author
  • Author Footnotes
    † These authors contributed equally to this work.
Published:March 16, 2019DOI:https://doi.org/10.1016/j.rbmo.2019.03.099

      Abstract

      This meta-analysis and systematic review investigated evidence of the effect of oral micronutrient supplementation on male fertility. Following searches of PubMed, Ovid/Ovid Medline(r) and Embase, 18 randomized, double-blind, placebo-controlled trials were included in the meta-analysis (seven studies) and/or the systematic review (12 studies). The meta-analysis showed significant improvement in semen parameters for selenium (200µg/day and 100µg/day) (standard mean difference [SMD] 0.64 for oligozoospermia, 1.39 for asthenozoospermia), L-carnitine (2 g/day) and acetyl-L-carnitine (LAC; 1 g/day) combined (SMD 0.57 for asthenozoospermia), and co-enzyme Q10 (200 and 300 mg/day) (SMD 0.95 for oligozoospermia, 1.48 for asthenozoospermia, 0.63 for teratozoospermia). The systematic review identified promising data for supplementation with 66 mg/day zinc combined with folic acid (5 mg/day), and the polyunsaturated fatty acids eicosapentaenoic acid (EPA; 1.12 g/day) and docosahexaenoic acid (DHA; 0.72 g/day). Pregnancy rate was evaluated in a limited number of trials (four in the meta-analysis, three in the systematic review). This analysis suggests supplementation with selenium (alone or combined with N-acetylcysteine), co-enzyme Q10 and the combinations L-carnitine + acetyl-L-carnitine, folic acid + zinc and EPA + DHA is beneficial in the treatment of male infertility. Because of the small number of available studies and low number of participants, further well-designed clinical studies are needed to obtain a better overview of efficient methods of treating male infertility.

      Keywords

      Introduction

      According to the World Health Organization, infertility is a disease of the reproductive system defined by a failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse (
      • Zegers-Hochschild F.
      • Adamson G.D.
      • de Mouzon J.
      • Ishihara O.
      • Mansour R.
      • Nygren K.
      • Sullivan E.
      • Vanderpoel S.
      'International Committee for Monitoring Assisted Reproductive Technology (ICMART) and the World Health Organization (WHO) revised glossary of ART terminology, 2009′.
      ). Fertility problems increasingly concern couples in present times. Agarwal and colleagues recently suggested that 20–70% of fertility problems are caused by the male partner (
      • Agarwal A.
      • Mulgund A.
      • Hamada A.
      • Chyatte M.R.
      ‘A unique view on male infertility around the globe’.
      ). This range exhibited large geographical differences, with the highest rates detected in Africa and central/eastern Europe. According to this report, a total of 48.5 million couples worldwide suffer from infertility, suggesting that 15% of couples are affected by fertility problems.
      One of the causes of male infertility is a reduced or poor sperm quality. Three primary end-points are normally determined to assess sperm quality: sperm concentration, sperm morphology and sperm motility. Although several micronutrient supplementation products are available on the market that promise to improve the spermiogram, there are only a few existing evidence-based data that address male factor infertility and micronutrient treatment options. The aim of this analysis was, based on published research, to make recommendations regarding micronutrient supplementation for men suffering from infertility. The evaluated parameters were change in sperm concentration, morphology and motility as well as the change in pregnancy rate following supplementation with the vitamins and minerals compared with placebo supplementation.

      Materials and methods

      The meta-analysis and systematic review were based on a systematic database review of randomized, double-blind, placebo-controlled studies that assessed the effect of micronutrient and vitamin supplementation on semen analysis of men suffering from infertility not caused by pathological diseases such as varicocele. The analysis was conducted to compare different micronutrient supplements, alone or in combination, versus placebo with regard to four measured end-points: (i) change in sperm concentration, (ii) change in sperm motility, (iii) change in sperm morphology, and (iv) change in pregnancy rate.
      The PubMed, Ovid/Ovid Medline(r) and Embase electronic databases were used for the literature review in May 2017. The following word combinations were used for a first general search: ‘male’, ‘fertility’ and ‘infertility’ in combination with ‘vitamin’ and ‘supplementation’. a specific search was also performed for every single micronutrient (Table 1) in combination with the terms ‘male’ and ‘fertility’ and, in a second step, ‘male’ and ‘infertility’, respectively. These search terms were used simultaneously in the databases mentioned above.
      Table 1Supplements included in the search and studies identified
      SupplementNumber of studies for analysis (authors, year)
      Vitamins
       Vitamin A
       Vitamin B6
       Vitamin B12
       Vitamin C1 (
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      )
       Vitamin D
       Vitamin E2 (
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ,
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      )
       Folic acid2 (
      • da Silva T.M.
      • Maia M.C.S.
      • Arruda J.T.
      • Approbato F.C.
      • Mendonca C.R.
      • Approbato M.S.
      'Folic acid does not improve semen parametrs in subfertile men: A double-blin, randomized, placebo-controlled study'.
      ,
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      )
      Trace elements
       Copper
       Iodide
       Zinc1 (
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      )
       Manganese
       Nickel
       Selenium3 (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ,
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      ,
      • Hawkes W.C.
      • Alkan Z.
      • Wong K.
      'Selenium supplementation does not affect testicular selenium status or semen quality in North American men'.
      )
      Other substances
      l-Arginine1 (
      • Pryor J.P.
      • Blandy J.P.
      • Evans P.
      • Chaput de Saintonge D.M.
      • Usherwood M.
      'Controlled Clinical Trial of Arginine for Infertile Men with Oligozoospermia'.
      )
       Docosahexaenoic acid2 (
      • Conquer J.A.
      • Martin J.B.
      • Tummon I.
      • Watson L.
      • Tekpetey F.
      'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
      ,
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
       Eicosapentaenoic acid1 (
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
      )
      L-Carnitine/ L-acetyl-carnitine3 (
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ,
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ,
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      )
       N-Acetylcysteine1 (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      )
       Co-enzyme Q105 (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Nadjarzadeh A.
      • Shidfar F.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Nazeri Kakhki S.A.
      • Akhondi M.M.
      • Sadeghi M.R.
      'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ,
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      )
       Beta-carotene
       Lutein

      Inclusion criteria

      The study included all randomized, placebo-controlled, double-blind studies that assessed change in sperm concentration, sperm motility and sperm morphology following oral administration of vitamin supplements and trace elements, alone or in combination, respectively.

      Exclusion criteria

      The study excluded case reports, reviews, meta-analyses and studies concerning men with varicocele or other diseases that could be considered to be causal for fertility problems, as well as pharmacokinetic studies.
      The study research was performed by one author (A.S.). Limitations applied within the data research process were ‘clinical trial’ and ‘human’. All substances used for the research are shown in Table 1. Study selection, quality assessment via data collection sheets (designed according to the standards of the Cochrane Collaboration Book version 5.1.0 https://handbook-5-1.cochrane.org/ ) and data extraction were performed independently and blindly by two authors (E.L. and A.S.). The data were then compared and any discrepancies were resolved by a third author (K.B.). A risk of bias was assessed for the included studies by two reviewers independently according to the guidelines of the Cochrane Collaboration Handbook version 5.1 and by Jadad Scale score (
      • Jadad A.R.
      • Moore R.A.
      • Carroll D.
      • Jenkinson C.
      • Reynolds D.J.
      • Gavaghan D.J.
      • McQuay H.J.
      'Assessing the quality of reports of randomized clinical trials: is blinding necessary? '.
      ). The Jadad Scale assesses following items: (i) is a study randomized?; (ii) is the method of randomization appropriate?; (iii) is a study double-blind?; (iv) is the method of blinding appropriate?; (v) is there any description of drop out?
      Only studies with ethical approval were included in the meta-analysis and systematic review.
      Heterogeneity was tested using the I-squared test.
      The meta-analysis was performed using statistical software Stata/SE 14.1 for Windows (StataCorp LLC, 4905 Lakeway Drive, College Station, Texas 77845-4512 USA) . The risk ratio for each analysis end-point, as well as the respective 95% confidence intervals (95% CI) and the impact of each study according to size, was calculated. In the absence of a standard deviation for the differences between before and after values for the substituted supplement and placebo, the standard deviation of the after-treatment values was used for the meta-analysis.

      Results

      The original database research included 21 supplements (Table 1). The detailed process of study selection is shown in Figure 1. The literature search identified 557 articles, which were first analysed by title and abstract. Based on the exclusion criteria, 514 studies were excluded. After evaluation of the remaining 43 studies with the data collection sheet, 22 studies were excluded as they either did not fulfil the inclusion criteria or were not available in English. A further three studies were excluded due to missing data.
      Figure 1
      Figure 1Study selection process.
      *The study by
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      is included in both the meta-analysis and systematic review.
      After the study selection process, 18 clinical studies (
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ,
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Conquer J.A.
      • Martin J.B.
      • Tummon I.
      • Watson L.
      • Tekpetey F.
      'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
      ,
      • da Silva T.M.
      • Maia M.C.S.
      • Arruda J.T.
      • Approbato F.C.
      • Mendonca C.R.
      • Approbato M.S.
      'Folic acid does not improve semen parametrs in subfertile men: A double-blin, randomized, placebo-controlled study'.
      ,
      • Hawkes W.C.
      • Alkan Z.
      • Wong K.
      'Selenium supplementation does not affect testicular selenium status or semen quality in North American men'.
      ,
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ,
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ,
      • Nadjarzadeh A.
      • Shidfar F.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Nazeri Kakhki S.A.
      • Akhondi M.M.
      • Sadeghi M.R.
      'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
      ,
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Pryor J.P.
      • Blandy J.P.
      • Evans P.
      • Chaput de Saintonge D.M.
      • Usherwood M.
      'Controlled Clinical Trial of Arginine for Infertile Men with Oligozoospermia'.
      ,
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ,
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
      ,
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ,
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      ,
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      ,
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      ,
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      ) involving 11 different supplements were included in the analysis. After performing the first statistical interpretation, 11 studies fulfilling all inclusion criteria could not be included in the meta-analysis because of heterogeneity (e.g. study design, applied dose or number of participants) so were described instead in the systematic review (
      • Conquer J.A.
      • Martin J.B.
      • Tummon I.
      • Watson L.
      • Tekpetey F.
      'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
      ,
      • da Silva T.M.
      • Maia M.C.S.
      • Arruda J.T.
      • Approbato F.C.
      • Mendonca C.R.
      • Approbato M.S.
      'Folic acid does not improve semen parametrs in subfertile men: A double-blin, randomized, placebo-controlled study'.
      ,
      • Hawkes W.C.
      • Alkan Z.
      • Wong K.
      'Selenium supplementation does not affect testicular selenium status or semen quality in North American men'.
      ,
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ,
      • Nadjarzadeh A.
      • Shidfar F.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Nazeri Kakhki S.A.
      • Akhondi M.M.
      • Sadeghi M.R.
      'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
      ,
      • Pryor J.P.
      • Blandy J.P.
      • Evans P.
      • Chaput de Saintonge D.M.
      • Usherwood M.
      'Controlled Clinical Trial of Arginine for Infertile Men with Oligozoospermia'.
      ,
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      ,
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
      ,
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      ,
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      ,
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      ).
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      was included in both the systematic review and the meta-analysis.

      Meta-analysis

      Seven randomized, placebo-controlled, double-blind studies –
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ,
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      ,
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ,
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ,
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      and
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      – were analysed within this meta-analysis (Table 2). These studies included 644 men suffering from infertility. Based on the selected studies, three meta-analyses with the end-points of change of sperm concentration, sperm motility and sperm morphology were performed. The data concerning the following supplements were assessed by meta-analysis: selenium, L-carnitine in combination with L-acetyl-carnitine, and co-enzyme Q10. The risk of bias could be identified in nearly all of the included studies (Table 3).
      Table 2Summary of the studies included in the meta-analysis
      SupplementAuthors (year)Days of sexual abstinenceTreatment/doseNumber receiving supplementNumber receiving placebo
      Selenium
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      2–5200 µg105106
      Selenium
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      4100 µg1618
      LC + LAC
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      No data2 g LC + 1 g

      LAC
      1415
      LC + LAC
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      52 g LC + 1 g

      LAC
      3026
      Co-enzyme Q10
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      3–7200 mg2324
      Co-enzyme Q10
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      3300 mg106106
      Co-enzyme Q10
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      No data200 mg2827
      LAC, L-acetyl-carnitine; LC, L-carnitine.
      Table 3Risk of bias for studies included in the meta-analysis
      Authors (year)Investigated supplementSelection biasPerformance biasAttrition biasReporting biasJadad Scale score
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      SeleniumMinimal riskMinimal riskMinimal riskNot clear if all results are reported

      (e.g. pregnancy rates)
      5
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      SeleniumMinimal riskPossiblePossibleNot clear if all results are reported

      (e.g. change of teratozoospermia)
      4
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      LC + LACMinimal riskMinimal riskMinimal riskMinimal risk3
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      LC + LACNo description of method of randomizationMinimal riskPossible, all four drop outs within placebo groupMinimal risk4
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      Co-enzyme Q10No description of method of randomizationMinimal riskPossible, 13 drop outs within treatment periodNot clear if all results are reported4
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      Co-enzyme Q10Minimal riskMinimal riskPossible, 25 drop outs within treatment periodNot clear if all results are reported (e.g. Pregnancy rates)5
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      Co-enzyme Q10No description of method of randomizationMinimal riskMinimal risk (five dropouts altogether in both groups)Minimal risk3
      LAC, L-acetyl-carnitine; LC, L-carnitine.
      Sperm parameters before and after treatment and evaluation of pregnancy rates in the included studies are summarised in Tables 4 and 5, respectively.
      Table 4Sperm parameters before and after receiving supplements or placebo in the studies included in the meta-analysis
      SupplementAuthors (year)Before treatmentAfter treatmentBefore placeboAfter placebo
      Oligozoospermia (106/ml)
       Selenium
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      22.40 ± 5.227.60 ± 6.4022.20 ± 5.1023.50 ± 5.80
       Selenium
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      39.80 ± 6.748.70 ± 8.8024.70 ± 5.8027.50 ± 10.00
       LC + LAC
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      29.40 ± 9.3937.40 ± 16.4229.53 ± 10.0733.73 ± 14.36
       LC + LAC
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      18.07 ± 5.6822.09 ± 9.0516.12 ± 7.7922.17 ± 16.95
       Co-enzyme Q10
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      16.13 ± 10.7016.09 ± 12.9019.77 ± 11.1016.21 ± 12.70
       Co-enzyme Q10
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      20.20 ± 4.6026.40 ± 4.4022.40 ± 4.4020.80 ± 4.30
       Co-enzyme Q10
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      42.39 ± 18.1144.93 ± 19.3050.14 ± 21.5546.37 ± 19.77
      Asthenozoospermia (%)
       Selenium
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      22.10 ± 2.6026.10 ± 2.9022.20 ± 2.2022.90 ± 2.20
       Selenium
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      21.60 ± 4.1030.20 ± 5.7018.10 ± 4.3015.30 ± 4.10
       LC + LAC
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      44.53 ± 11.8461.07 ± 9.0743.93 ± 10.2643.40 ± 9.85
       LC + LAC
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      23.17 ± 6.5031.11 ± 13.4623.08 ± 6.4929.55 ± 9.50
       Co-enzyme Q10
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      36.13 ± 17.9041.91 ± 15.6037.79 ± 15.9038.33 ± 18.40
       Co-enzyme Q10
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      22.20 ± 2.4027.60 ± 2.2022.30 ± 2.6023.10 ± 2.10
       Co-enzyme Q10
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      33.14 ± 7.1239.41 ± 6.8034.81 ± 8.3934.93 ± 8.04
      Teratozoospermia (%)
       LC + LAC
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      67.13 ± 6.0159.60 ± 5.8268.20 ± 5.8667.27 ± 6.71
       LC + LAC
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      76.87 ± 4.1075.59 ± 7.7975.42 ± 5.2271.11 ± 9.10
       Co-enzyme Q10
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      7.43 ± 5.106.52 ± 5.106.08 ± 5.606.29 ± 4.30
       Co-enzyme Q10
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      7.20 ± 2.609.60 ± 2.407.30 ± 2.707.80 ± 2.10
      Results are given +/- standard deviation.
      LAC, L-acetyl-carnitine; LC, L-carnitine.
      Table 5Occurrence of pregnancy within the observation period of studies included into meta-analysis
      SupplementAuthors (year)Pregnancy occurrence
      Selenium
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      No data
      Selenium
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      Five participants from the treatment group became spontaneously pregnant after the treatment period
      LC + LAC
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      A total of 12 spontaneous pregnancies: nine in the treatment group, three in the placebo group
      LC + LAC
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      Four spontaneous pregnancies, all within the treatment group
      Co-enzyme Q10
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      No data
      Co-enzyme Q10
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      No pregnancies
      Co-enzyme Q10
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      Nine spontaneous pregnancies: six in the treatment group, three in the placebo group
      LAC, L-acetyl-carnitine; LC, L-carnitine.

      Selenium

      Two studies concerning selenium substitution were assessed by meta-analysis.
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      administered selenium at a dose of 200 µg (orally, daily) for 26 weeks, whereas Scott and colleagues (
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      ) used 100 µg for 12 weeks (orally, daily). The study by Safarinejad and Safarinejad (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ) made the largest contribution to the meta-analysis, accounting for at least 86% of the subjects. Only oligozoospermia and asthenozoospermia could be analysed. No analysis was performed for teratozoospermia because of missing data. The meta-analyses showed that the effect of selenium supplementation was significantly higher than that of placebo, with a standard mean difference (SMD) of 0.64 (95% CI 0.38–0.90) and 1.39 (95% CI 1.11–1.67) for oligozoospermia (Figure 2) and asthenozoospermia (Figure 3), respectively.
      Figure 2
      Figure 2End-point analysis of studies investigating the impact of different supplements on changes in oligozoospermia compared with placebo (forest plot). CI, confidence interval; LAC, L-acetyl-carnitine; LC, L-carnitine; SMD, standard mean difference.
      Figure 3
      Figure 3End-point analysis of studies investigating the impact of different supplements on changes in asthenozoospermia compared with placebo (forest plot). CI, confidence interval; LAC, L-acetyl-carnitine; LC, L-carnitine; SMD, standard mean difference.
      The I-squared test resulted in a variability of 0.0% for oligozoospermia and 79.1% for asthenozoospermia, indicating substantial heterogeneity of the analysed studies.

      L-Carnitine and acetyl-L-carnitine

      The studies by Balercia and colleagues (
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ) and Lenzi and co-workers (
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ) were assessed in the meta-analysis. Both studies supplemented a dose of 2 g of L-carnitine in combination with a dose of 1 g of acetyl-L-carnitine for 6 months. Lenzi and colleagues (
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ) provided a greater contribution to all the meta-analyses, accounting for at least 66% of the participants. All three end-points were analysed. The meta-analysis did not show a significant improvement in carnitine group with respect to oligozoospermia (SMD –0.02; 95% CI –0.44 to 0.41; Figure 2).
      Overall, the meta-analysis of asthenozoospermia showed significantly better results for the carnitine group (SMD 0.57; 95% CI 0.12–1.02; Figure 3).
      The meta-analysis related too teratozoospermia (measured as atypical sperm cells) showed no difference between the supplement and placebo groups (SMD –0.08; 95% CI –0.52 to 0.35; Figure 4).
      Figure 4
      Figure 4End-point analysis of studies investigating the impact of different supplements on changes in teratozoospermia compared with placebo (forest plot). CI, confidence interval; LAC, L-acetyl-carnitine; LC, L-carnitine; SMD, standard mean difference.
      Overall, the intake of L-carnitine in combination with acetyl-L-carnitine did not result in an unambiguous improvement of all tested parameters. For the subgroup analysis of L-carnitine+acetyl-L-carnitine the I-squared test resulted in great variability: from 0.0% for oligozoospermia to 90.4% for asthenozoospermia and 88.3% for teratozoospermia, again indicating substantial heterogeneity of the analysed studies.

      Co-enzyme Q10

      Three studies (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ) were included in the meta-analysis of the influence of co-enzyme Q10 on sperm parameters. In these studies, co-enzyme Q10 was supplemented at a dose of 200 or 300 mg (orally, daily) for different durations of 12 weeks to 26 weeks. All three end-points were significantly improved in the co-enzyme Q10 groups compared with the placebo groups in the meta-analysis. For oligozoospermia, an SMD of 0.95 (95% CI 0.72–1.19; Figure 2) was determined.
      With respect to asthenozoospermia, the effect size is mapped out as an SMD of 1.48 (95% CI 1.23–1.74; Figure 3). Teratozoospermia (measured as normal morphology) was also significantly improved in the group given supplements (SMD 0.63; 95% CI 0.38–0.89; Figure 4).
      The I-squared test resulted in variability ranging from 88.2% for oligozoospermia to 94.4% for asthenozoospermia and 90.9% for teratozoospermia, indicating substantial heterogeneity of the analysed studies.

      Systematic review

      Eleven supplements were analysed in form of a systematic review: N-acetylcysteine and selenium as single agents and in combination, folic acid (alone and in combination with zinc), the antioxidant vitamins C and E, l-arginine, the polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), L-carnitine /LAC and co-enzyme Q10.

      N-acetylcysteine and selenium as single agents or in combination

      Safarinejad and Safarinejad (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ) analysed the administration of N-acetylcysteine (600 mg orally, daily) and selenium (200 µg orally, daily) as single agents or in combination in a randomized placebo-controlled trial.
      The analysis of all measured semen characteristics (sperm concentration, motility and strict morphology) showed significantly higher values in the supplement group than the placebo group after 26 weeks. Sperm concentration improved from 22.4 ± 5.2 to 27.6 ± 6.4  ×  106/ml (P = 0.03) in the selenium group, and from 22.6 ± 5.4 to 26.8 ± 5.3  ×  106/ml (P = 0.04) in the N-acetylcysteine group. A significant improvement was also evident in the group treated with both selenium and N-acetylcysteine, with values increasing from 21.6 ± 4.4 to 32.1 ± 6.8  ×  106/ml (P = 0.01). Sperm motility (measured as the percentage of motile spermatozoa) improved in the selenium group from 22.1 ± 2.6% to 26.1 ± 2.9% (P = 0.03); however, in the N-acetylcysteine group, the change from 22.4 ± 2.6% to 24.8 ± 2.9% did not reach statistical significance (P = 0.07). The biggest improvement in motility occurred with combined treatment with selenium and N-acetylcysteine, with an increase from 22.8 ± 2.4% to 29.2 ± 2.9% (P = 0.02). Strict morphology (measured as the percentage of normal spermatozoa) also improved significantly: from 7.2 ± 2.9% to 9.2 ± 2.9% (P = 0.03) in the selenium group, from 7.4 ± 2.8% to 9.2 ± 3.1% (P = 0.03) in the N-acetylcysteine group, and from 7.2 ± 2.8% to 9.3 ± 2.9% (P = 0.03) in the group treated with a combination of selenium and N-acetylcysteine.
      The selenium study by Hawkes and colleagues (
      • Hawkes W.C.
      • Alkan Z.
      • Wong K.
      'Selenium supplementation does not affect testicular selenium status or semen quality in North American men'.
      ) was excluded from the meta-analysis as the general conditions (high-dose selenium supplementation) differed substantially from those of the studies included in the meta-analysis. Sperm concentration and motility did not exhibit any differences over the course of the study, while sperm morphology (% of normal) increased in both groups but did not reach the level of significance.

      Folic acid

      Two randomized controlled trials assessed the effect of folic acid on sperm parameters. The study by Wong and co-workers (
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      ) included fertile and subfertile men and tested folic acid (5 mg/day) and zinc sulphate (66 mg/day) alone or in combination for 26 weeks against a placebo. In the subgroup of subfertile men, a significant increase in sperm concentration from 7.5 to 12.0  ×  106/ml (P < 0.001) was observed following the combined intake of zinc and folic acid. Da Silva and colleagues (
      • da Silva T.M.
      • Maia M.C.S.
      • Arruda J.T.
      • Approbato F.C.
      • Mendonca C.R.
      • Approbato M.S.
      'Folic acid does not improve semen parametrs in subfertile men: A double-blin, randomized, placebo-controlled study'.
      ) administered folic acid as a mono-preparation for 3 months (supplemented dose of 5 mg per day). The authors did not observe any significant improvements in sperm concentration, sperm motility and sperm morphology in the subgroup of subfertile men. The difference in the results in subfertile men is conceivably attributable to the additional administration of zinc sulphate in Wong and colleagues’ study (
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      ) or to the considerably longer duration of medication.
      Neither study evaluated the change in pregnancy rate. In addition, neither study could be included in the meta-analysis because of heterogeneous study designs (e.g. duration of medication).

      Antioxidant substances

      Two studies examined the effect of antioxidant compounds on the sperm parameters. Rolf and colleagues (
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      ) substituted high-dose vitamin C (1000 mg/day) and vitamin E (800 mg/day) simultaneously to men with asthenozoospermia or normal and moderately reduced sperm concentrations. The crossover trial of Kessopoulou and co-workers (
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ) administered only vitamin E (600 mg/day) to men with high concentrations of reactive oxygen species in their spermatozoa. No significant improvement in sperm concentration, sperm motility, sperm morphology and initiated pregnancies could be detected following antioxidant treatment compared with placebo in the two studies. The lack of effect of the antioxidants might be explained by the inclusion of men with a normal or moderately reduced spermiogram in Rolf and colleagues’ evaluation (
      • Rolf C.
      • Cooper T.G.
      • Yeung C.H.
      • Nieschlag E.
      'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
      ) and reactive oxygen species as a selection criterion by Kessopoulou and co-workers (
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ), or by the short duration of medication of only 8 and 12 weeks, respectively.

      L-arginine

      Pryor and co-workers (
      • Pryor J.P.
      • Blandy J.P.
      • Evans P.
      • Chaput de Saintonge D.M.
      • Usherwood M.
      'Controlled Clinical Trial of Arginine for Infertile Men with Oligozoospermia'.
      ) evaluated the effect of arginine supplementation on sperm parameters in a crossover trial: 4 g/day of arginine or matching placebo was given to infertile men suffering from oligozoospermia for a period of 12 weeks. After 12 weeks, the group receiving arginine was administered placebo, and the group receiving the placebo was administered arginine. After 24 weeks, the results did not show any significant differences in sperm count, sperm motility or sperm morphology between the treatment and placebo groups during the two experimental periods. Some interesting results were detected concerning the pregnancy rate: independent of poor semen quality, impaired spermatogenesis and elevated follicle-stimulating hormone, six wives of the trial participants (54 participants completed the trial) became pregnant. However, there were no differences in the pregnancy rate during the different periods of the study. It is unclear why the study only permitted the inclusion of men with a total motile sperm count of less than 10 million per ejaculate, whereas the title of the study names oligozoospermia as the basic assumption of the clinical trial.

      Polyunsaturated fatty acids EPA and DHA

      The effects of polyunsaturated fatty acids on semen parameters were evaluated based on two studies with substantially different study designs; the different supplementation regimens and doses made it impossible to include the results of this group in the meta-analysis. Safarinejad (
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
      ) gave EPA (1.12 g/day) and DHA (0.72 g/day) supplements in combination to men with idiopathic oligoasthenoteratospermia for 32 weeks. A significant improvement in oligozoospermia, asthenozoospermia and teratozoospermia (increase in sperm concentration from 15.6 ± 4.1 to 28.7 ± 4.4  ×  106/ml [P = 0.001], in motility [percentage motile] from 18.7 ± 2.4% to 27.4 ± 2.6% [P = 0.002] and in strict normal morphology from 7.4 ± 2.8% to 12.8 ± 2.6% [P = 0.002]) was shown. The study by Conquer and colleagues (
      • Conquer J.A.
      • Martin J.B.
      • Tummon I.
      • Watson L.
      • Tekpetey F.
      'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
      ) included asthenozoospermic men and used DHA only at a dose of 400 or 800 mg/day for 3 months. No significant improvement was observed in oligozoospermia and asthenozoospermia (a change in sperm concentration from 31.6 ± 9.8 to 37.8 ± 12.3  ×  106/ml in the 400 mg group and 57.0 ± 17.6 to 44.6 ± 13.0  ×  106/ml in the 800 mg group; sperm motility (percentage of motile spermatozoa) increased from 26.7 ± 4.2 to 39.4 ± 8.1 in the 400 mg group and 25.3 ± 4.5 to 32.0 ± 5.1 in the 800 mg group). The effect on teratozoospermia was not evaluated. No P-values were published in that study. Change in pregnancy rate was not assessed in either study.

      Carnitine (L-carnitine and acetyl-L-carnitine)

      Sigman and colleagues (
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      ) administered L-carnitine (2000mg/day) and acetyl-L-carnitine (1000 mg/day) in combination and studied the resulting effects on sperm motility. As this study contains methodological deficiencies (e.g. missing values for standard deviation, a low number of participants and an unclear randomization method), it could not be included in the meta-analysis, and thus the results should be interpreted with caution. Sigman and colleagues (
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      ) did not show any significant effect on sperm motility or total motile sperm count, while two pregnancies occurred during the study period.
      Overall, all studies assessing the administration of carnitine provide heterogeneous results for different end-points in the spermiogram.

      Co-enzyme Q

      Five studies that investigated the effect of co-enzyme Q remained after the study selection process. Three studies were compared in the meta-analysis (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ). The meta-analysis yielded significantly better results for the co-enzyme Q groups. One additional study by Safarinejad and colleagues (
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      ), assessing a dose of 200 mg/day for 26 weeks, showed a significant increase in sperm density, motility and morphology in the treatment group compared with the placebo group (n = 228). Nadjarzadeh and colleagues (
      • Nadjarzadeh A.
      • Shidfar F.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Nazeri Kakhki S.A.
      • Akhondi M.M.
      • Sadeghi M.R.
      'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
      ) also investigated the influence of administering co-enzyme Q10 (200 mg/day) to men suffering from oligoasthenoteratozoospermia, although a much smaller number of participants (n = 47) completed the 3-month trial. There were no significant increases in sperm count, motility and morphology.

      Discussion

      The aim of this analysis was to provide a comprehensive overview of the evidence concerning the treatment of male infertility and micronutrient supplementation.
      The strength of this review lies the strict criteria regarding the inclusion of studies: only well-designed, randomized, placebo-controlled, double-blind trials were included in the analysis. The data concerning 11 supplements were analysed in the form of a meta-analysis and/or systematic review.
      The limitation of the present analysis is the small number of trials included (due to the strict inclusion criteria) and, correspondingly, the limited number of patients in the treatment groups. Nevertheless, we believe that the results have a high scientific value for future research. The studies included in the meta-analysis frequently showed high heterogeneity, which is represented in the forest plots (Figure 2, Figure 3, Figure 4). Furthermore, the risk of bias could be identified in nearly all of the included studies (Table 3). Unfortunately, the majority of the available studies do not report the change in pregnancy rates, which is the decisive factor in the treatment of involuntary childlessness.
      One important aspect relating to sperm quality is the period of sexual abstinence. Unfortunately, the included studies showed great variety, demanding from 2 to 7 days of sexual abstinence before collecting semen samples (details of the studies included in the meta-analysis are shown in Table 2). Five of the 18 included studies (
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ,
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Conquer J.A.
      • Martin J.B.
      • Tummon I.
      • Watson L.
      • Tekpetey F.
      'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
      ,
      • Kessopoulou E.
      • Powers H.J.
      • Sharma K.K.
      • Pearson M.J.
      • Russell J.M.
      • Cooke I.D.
      • Barratt C.L.R.
      'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
      ,
      • Sigman M.
      • Glass S.
      • Campagnone J.
      • Pryor J.L.
      'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
      ) revealed no information about the period of sexual abstinence. Therefore, the role of sexual abstinence as a confounding factor, as well as the role of lifestyle variables, cannot be finally assessed because of missing data.
      Overall, the meta-analysis shows a significant improvement in some sperm parameters for the following supplements: selenium, a combination of L-carnitine and acetyl-L-carnitine, and co-enzyme Q10. The meta-analysis including the studies by Safarinejad and Safarinejad (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ) and Scott and colleagues (
      • Scott R.
      • MacPherson A.
      • Yates R.W.S.
      • Hussain B.
      • Dixon J.
      'The effect of oral selenium supplementation on human sperm motility'.
      ) was able to show a significant improvement in oligozoospermia and asthenozoospermia after supplementation with selenium compared with placebo, whereas there are no published data for teratozoospermia within the primary data. The meta-analysis including the studies by Balercia and co-workers (
      • Balercia G.
      • Regoli F.
      • Armeni T.
      • Koverech A.
      • Mantero F.
      • Boscaro M.
      ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
      ) and Lenzi and co-workers (
      • Lenzi A.
      • Sgro P.
      • Salacone P.
      • Paoli D.
      • Gilio B.
      • Lombardo F.
      • Santulli M.
      • Agarwal A.
      • Gandini L.
      'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
      ) showed a significant improvement only for asthenozoospermia after supplementation with L-carnitine + acetyl-L-carnitine. Clear recommendations for supplementation with carnitine are therefore not possible. Further investigations are needed to determine the role of L-carnitine and acetyl-L-carnitine in the treatment of male infertility. The meta-analysis including the studies of Nadjarzadeh and colleagues (
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ), Balercia and colleagues (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ) and Safarinejad (
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ) was able to show a significant improvement in all measured end-points (oligozoospermia, asthenozoospermia and teratozoospermia) in relation to supplementation with co-enzyme Q10. This meta-analysis points out new perspectives on the treatment of male infertility, albeit from a small number of studies and small sample sizes.
      This systematic review identified positive effects in treating male infertility for the following supplements: N-acetylcysteine alone or in combination with selenium, a combination of zinc and folic acid, a combination of EPA and DHA, and co-enzyme Q10. Supplementation with N-acetylcysteine (alone or in combination with selenium) was evaluated in one study (
      • Safarinejad M.R.
      • Safarinejad S.
      'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
      ). A significant improvement in all three end-points (oligozoospermia, asthenozoospermia and teratozoospermia) was shown after treatment with N-acetylcysteine and a combination of N-acetylcysteine and selenium. A significant improvement in sperm concentration was shown in one study (
      • Wong W.Y.
      • Merkus H.M.W.M.
      • Thomas C.M.G.
      • Menkveld R.
      • Zielhuis G.A.
      • Steegers-Theunissen R.P.M.
      'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
      ) in relation to a combination of zinc and folic acid. Concerning the combination of EPA and DHA, one available study (
      • Safarinejad M.R.
      'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
      ) showed significantly better results in the treatment group than the placebo group for all three end-points. Further studies are required to determine whether EPA supplementation has a decisive role in the influence of polyunsaturated fatty acids on the spermiogram.
      Overall, three of the five studies concerning Q10 supplementation (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ,
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ,
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      ) showed significantly improved results for the following end-points.
      Balercia and co-workers (
      • Balercia G.
      • Buldreghini E.
      • Vignini A.
      • Tiano L.
      • Paggi F.
      • Amoroso S.
      • Ricciardo-Lamonica G.
      • Boscaro M.
      • Lenzi A.
      • Littarru G.
      ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
      ) showed signifiant improvements for asthenozoospermia while there was no significant improvement for oligozoospermia. As morphology was measured as atypical sperm cells, it could not be included in the meta-analysis and was not able to show any significant improvement. Safarinejad (
      • Safarinejad M.R.
      'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
      ) reported significantly better results for all three end-points (oligozoospermia, asthenozoospermia and teratozoospermia). A study by Safarinejad and colleagues (
      • Safarinejad M.R.
      • Safarinejad Shiva.
      • Shafiei N.
      • Safarinejad Saba.
      'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
      ) that was one of two studies included in the systematic review also showed significantly better results for all three parameters tested (sperm density, motility and morphology).
      The studies by Nadjarzadeh and colleagues (
      • Nadjarzadeh A.
      • Sadeghi M.R.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Akhondi M.A.
      • Yavari P.
      • Shidfar F.
      'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
      ,
      • Nadjarzadeh A.
      • Shidfar F.
      • Amirjannati N.
      • Vafa M.R.
      • Motevalian S.A.
      • Gohari M.R.
      • Nazeri Kakhki S.A.
      • Akhondi M.M.
      • Sadeghi M.R.
      'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
      ) were not able to confirm these significant findings, so the reason for them remains unclear. One possible explanation could lie in the short duration of medication (only 3 months). However, the intake of co-enzyme Q10 can be recommended for the treatment of male infertility.
      In conclusion, the current analysis shows significantly better results for the intake of selenium (alone or in combination with N-acetylcysteine), a combination of zinc and folic acid, a combination of EPA and DHA, a combination of L-carnitine and LAC, and co-enzyme Q10. The level of evidence concerning supplementation with the other promising micronutrients is insufficient. Further well-designed clinical studies are needed to identify the influence on male fertility of supplementation with vitamins and minerals.
      With respect to the mechanism of action of the substances investigated, the following data are available. The positive effect of zinc can be explained by the fact that zinc plays an important role in the cell cycle and stabilizes concentrations of testosterone in both infertile and healthy men (
      • Prasad A.S.
      • Mantzoros C.S.
      • Beck F.W.
      • Hess J.W.
      • Brewer G.J.
      'Zinc status and serum testosterone levels of healthy adults'.
      ). Polyunsaturated fatty acids such as EPA and DHA are an integral part of the cell membrane, which helps to stabilize individual cells.
      To the best of our knowledge, the mode of action of selenium in male infertility has not yet been fully clarified, although there are some data concerning its role in protection against oxidative stress (
      • Tinggi U.
      'Selenium: its role as antioxidant in human health'.
      ). In general, antioxidant substances are thought to stabilize cell membranes and protect the cell against free radicals (
      • Pham-Huy L.A.
      • He H.
      • Pham-Huy C.
      'Free radicals, antioxidants in disease and health'.
      ). For example, co-enzyme Q10 is known for its antioxidant potential, and its positive impact on male fertility has been demonstrated. Paradoxically, however, no improvement in the tested parameters could be shown for the antioxidant vitamins C and E in the current analysis.
      Based on these findings, it can be concluded that further studies with larger homogeneous cohorts are necessary to assess the effect of vitamins and minerals on the spermiogram, so that final recommendations concerning supplements in the treatment of male factor infertility can be provided.

      References

        • Agarwal A.
        • Mulgund A.
        • Hamada A.
        • Chyatte M.R.
        ‘A unique view on male infertility around the globe’.
        Reprod Biol Endocrinol. 2015; 13: 37
        • Balercia G.
        • Buldreghini E.
        • Vignini A.
        • Tiano L.
        • Paggi F.
        • Amoroso S.
        • Ricciardo-Lamonica G.
        • Boscaro M.
        • Lenzi A.
        • Littarru G.
        ‘Coenzyme Q10 treatment in infertile men with idiopathic asthenozoospermia: a placebo-controlled, double-blind randomized trial’.
        Fertil Steril. 2009; 91: 1785-1792
        • Balercia G.
        • Regoli F.
        • Armeni T.
        • Koverech A.
        • Mantero F.
        • Boscaro M.
        ‘Placebo-controlled double-blind randomized trial on the use of l-carnitine, l-acetylcarnitine, or combined l-carnitine and l-acetylcarnitine in men with idiopathic asthenozoospermia'.
        Fertil Steril. 2005; 84: 662-671
        • Conquer J.A.
        • Martin J.B.
        • Tummon I.
        • Watson L.
        • Tekpetey F.
        'Effect of DHA Supplementation on DHA Status and Sperm Motility in Asthenozoospermic Males'.
        Lipids. 2000; 35: 149-154
        • da Silva T.M.
        • Maia M.C.S.
        • Arruda J.T.
        • Approbato F.C.
        • Mendonca C.R.
        • Approbato M.S.
        'Folic acid does not improve semen parametrs in subfertile men: A double-blin, randomized, placebo-controlled study'.
        JBRA Assist. Reprod. 2013; 17: 152-157
        • Hawkes W.C.
        • Alkan Z.
        • Wong K.
        'Selenium supplementation does not affect testicular selenium status or semen quality in North American men'.
        J Androl. 2009; 30: 525-533
        • Jadad A.R.
        • Moore R.A.
        • Carroll D.
        • Jenkinson C.
        • Reynolds D.J.
        • Gavaghan D.J.
        • McQuay H.J.
        'Assessing the quality of reports of randomized clinical trials: is blinding necessary? '.
        Control Clin.Trials. 1996; 17: 1-12
        • Kessopoulou E.
        • Powers H.J.
        • Sharma K.K.
        • Pearson M.J.
        • Russell J.M.
        • Cooke I.D.
        • Barratt C.L.R.
        'A double-blind randomized placebo cross-over controlled trial using the antioxidant vitamin E to treat reactive oxygen species associated male infertility*'.
        Fertil Steril. 1995; 64: 825-831
        • Lenzi A.
        • Sgro P.
        • Salacone P.
        • Paoli D.
        • Gilio B.
        • Lombardo F.
        • Santulli M.
        • Agarwal A.
        • Gandini L.
        'A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and L-acetyl-carnitine treatment in men with asthenozoospermia'.
        Fertil Steril. 2004; 81: 1578-1584
        • Nadjarzadeh A.
        • Sadeghi M.R.
        • Amirjannati N.
        • Vafa M.R.
        • Motevalian S.A.
        • Gohari M.R.
        • Akhondi M.A.
        • Yavari P.
        • Shidfar F.
        'Coenzyme Q10 improves seminal oxidative defense but does not affect on semen parameters in idiopathic oligoasthenoteratozoospermia: a randomized double-blind, placebo controlled trial'.
        J Endocrinol Invest. 2011; 34: e224-e228
        • Nadjarzadeh A.
        • Shidfar F.
        • Amirjannati N.
        • Vafa M.R.
        • Motevalian S.A.
        • Gohari M.R.
        • Nazeri Kakhki S.A.
        • Akhondi M.M.
        • Sadeghi M.R.
        'Effect of Coenzyme Q10 supplementation on antioxidant enzymes activity and oxidative stress of seminal plasma: a double-blind randomised clinical trial'.
        Andrologia. 2014; 46: 177-183
        • Pham-Huy L.A.
        • He H.
        • Pham-Huy C.
        'Free radicals, antioxidants in disease and health'.
        Int J Biomed Sci. 2008; 4: 89-96
        • Prasad A.S.
        • Mantzoros C.S.
        • Beck F.W.
        • Hess J.W.
        • Brewer G.J.
        'Zinc status and serum testosterone levels of healthy adults'.
        Nutrition. 1996; 12: 344-348
        • Pryor J.P.
        • Blandy J.P.
        • Evans P.
        • Chaput de Saintonge D.M.
        • Usherwood M.
        'Controlled Clinical Trial of Arginine for Infertile Men with Oligozoospermia'.
        Br J Urol. 1978; 50: 47-50
        • Rolf C.
        • Cooper T.G.
        • Yeung C.H.
        • Nieschlag E.
        'Antioxidant treatment of patients with asthenozoospermia or moderate oligoasthenozoospermia with high-dose vitamin C and vitamin E: a randomized,placebo-controlled, double-blind study'.
        Human Reproduction. 1999; 14: 1028-1033
        • Safarinejad M.R.
        'Effect of omega-3 polyunsaturated fatty acid supplementation on semen profile and enzymatic anti-oxidant capacity of seminal plasma in infertile men with idiopathic oligoasthenoteratospermia: a double-blind, placebo-controlled, randomised study'.
        Andrologia. 2011; 43: 38-47
        • Safarinejad M.R.
        'Efficacy of coenzyme Q10 on semen parameters, sperm function and reproductive hormones in infertile men'.
        J Urol. 2009; 182: 237-248
        • Safarinejad M.R.
        • Safarinejad S.
        'Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study'.
        J Urol. 2009; 181: 741-751
        • Safarinejad M.R.
        • Safarinejad Shiva.
        • Shafiei N.
        • Safarinejad Saba.
        'Effects of the reduced form of coenzyme Q10 (ubiquinol) on semen parameters in men with idiopathic infertility: a double-blind, placebo controlled, randomized study'.
        J Urol. 2012; 188: 526-531
        • Scott R.
        • MacPherson A.
        • Yates R.W.S.
        • Hussain B.
        • Dixon J.
        'The effect of oral selenium supplementation on human sperm motility'.
        Br J Urol. 1998; 82: 76-80
        • Sigman M.
        • Glass S.
        • Campagnone J.
        • Pryor J.L.
        'Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial'.
        Fertil Steril. 2006; 85: 1409-1414
        • Tinggi U.
        'Selenium: its role as antioxidant in human health'.
        Environ Health Prev Med. 2008; 13: 102-108
        • Wong W.Y.
        • Merkus H.M.W.M.
        • Thomas C.M.G.
        • Menkveld R.
        • Zielhuis G.A.
        • Steegers-Theunissen R.P.M.
        'Effects of folic acid and zinc sulfate on male factor subfertility: a double-blind, randomized, placebo-controlled trial'.
        Fertil Steril. 2002; 77: 491-498
        • Zegers-Hochschild F.
        • Adamson G.D.
        • de Mouzon J.
        • Ishihara O.
        • Mansour R.
        • Nygren K.
        • Sullivan E.
        • Vanderpoel S.
        'International Committee for Monitoring Assisted Reproductive Technology (ICMART) and the World Health Organization (WHO) revised glossary of ART terminology, 2009′.
        Fertil Steril. 2009; 92: 1520-1524

      Biography

      Kai Buhling studied medicine in Hamburg and Berlin. He led a diabetes outpatient clinic from 1997 to 2005, and then worked in gynaecological and reproductive medicine. Since 2007, he has been Head of the Department of Gynecological Endocrinology and Reproductive Medicine of the University Hospital Hamburg-Eppendorf, Hamburg, Germany.
      Key message
      This analysis suggests that supplementation with selenium (alone or combined with N-acetylcysteine), a combination of EPA and DHA, co-enzyme Q10, a combination of zinc and folic acid, and a combination of L-carnitine and acetyl-L-carnitine may improve the spermiogram of infertile men. Further well-designed clinical studies are, however, necessary to provide treatment recommendations.