The evidence for supplements is weaker than the marketing. The 2022 Cochrane review of antioxidants for male subfertility found very low-certainty evidence that they may improve live birth rates (12 trials, 1,283 men), a benefit that disappeared when the trials at high risk of bias were removed, and concluded that "current evidence is inconclusive". The two largest recent trials agree: MOXI (174 men) found a combined antioxidant didn't improve any semen measure or live birth, and FAZST (2,370 men) found folic acid plus zinc didn't either. Some small trials of CoQ10 show higher concentration and motility without evidence that pregnancies follow. Diet, by contrast, is consistently linked to better semen quality.
The Cochrane conclusion
The Cochrane review (de Ligny and colleagues, 2022) is the most careful summary of the antioxidant trials, and its findings are worth stating precisely because they are so often quoted loosely. For live birth, 12 small or medium randomized trials involving 1,283 men gave an odds ratio of 1.43 in favor of antioxidants, graded very low certainty; when the eight trials at lower risk of bias were analyzed alone, the odds ratio fell to 1.22 with a confidence interval that included no effect. For clinical pregnancy, 20 trials and 1,706 men gave an odds ratio of 1.89, graded low certainty and resting on only 327 pregnancies. Antioxidants may increase mild stomach upset (odds ratio 2.70). The authors' conclusion is that the evidence is inconclusive and that large, well-designed, placebo-controlled trials are needed. The earlier 2019 version of the same review, which the app's science page cites, reached a similar place with slightly more optimistic wording.
The two large trials
MOXI (Steiner and colleagues, Fertility and Sterility, 2020) randomized 174 men with male-factor infertility to a daily combination of vitamin C (500 mg), vitamin E (400 mg), selenium, L-carnitine (1,000 mg), zinc (20 mg), folic acid (1,000 μg), lycopene and vitamin D, or placebo, for three to six months. There was no improvement in concentration, motility or morphology, no difference in DNA fragmentation at three months, and live birth was 15% in the antioxidant group against 24% on placebo, a difference that wasn't statistically significant. The authors' conclusion: antioxidants "do not improve semen parameters or DNA integrity among men with male factor infertility".
FAZST (Schisterman and colleagues, JAMA, 2020) randomized 2,370 men at four US fertility centers to 5 mg folic acid plus 30 mg zinc daily, or placebo, for six months. Live birth rates did not differ, semen quality did not improve, and the supplement group had slightly higher sperm DNA fragmentation at six months and more stomach complaints. It is one of the largest supplement trials ever run in men trying to conceive, and it was negative.
Ingredient by ingredient
CoQ10
A 2013 meta-analysis (Lafuente and colleagues) pooled three small placebo-controlled trials, 149 men on CoQ10 and 147 on placebo. Sperm concentration was about 5 million/mL higher and motility about 4.5 percentage points higher in the CoQ10 groups, and seminal CoQ10 rose sharply, which at least shows the supplement gets where it's meant to. Pregnancy rates didn't increase, and no trial reported live births. That is the honest summary: it moves a lab number a little in small trials, and nobody has shown it moves the outcome.
Zinc
A 2016 meta-analysis (Zhao and colleagues) of 20 studies found infertile men had lower zinc in seminal plasma than fertile men, and that supplementation was associated with better volume, motility and morphology, though the trials were small and varied. The much larger FAZST trial then gave 30 mg of zinc a day (with folic acid) to 1,185 men and found no benefit. Read together: a real association with zinc status, and no evidence that taking extra helps a man who isn't deficient. Zinc from food (shellfish, meat, beans, nuts, seeds) covers most people.
Folate
Folate matters for DNA synthesis, which is why it was a candidate. FAZST tested 5 mg a day for six months in over a thousand men and found no improvement in semen quality or live birth, with slightly higher DNA fragmentation in the supplement group. Leafy greens, lentils and chickpeas are the food sources.
Vitamin D
The best trial is Danish (Blomberg Jensen and colleagues, 2018): 330 infertile men randomized to a high-dose vitamin D regimen with calcium, or placebo, for about five months. Semen parameters didn't change and overall live birth didn't differ. In a secondary analysis of men with low sperm counts, live birth was 35.6% in the vitamin D group against 18.3% on placebo; a subgroup result like that is a reason for a dedicated trial, not a result in itself. If you are vitamin D deficient there are other reasons to correct it; as a sperm supplement, the trial doesn't support it.
Omega-3
A 2020 cross-sectional study of 1,679 young Danish men (Jensen and colleagues, JAMA Network Open) found fish oil supplement users had higher semen volume (0.64 mL more in men who'd used it for 60 days or longer), higher total sperm count, larger testes and lower FSH than non-users. It is an observational study of healthy young men, so it can't separate the supplement from the kind of man who takes it, and no trial has tested fish oil against placebo for these outcomes at scale. Oily fish twice a week gives you the omega-3 and the dietary pattern the diet studies favor.
Vitamins C and E, selenium, L-carnitine, lycopene
These are the standard antioxidant ingredients, and they are exactly what MOXI tested in combination and found no effect from. Individually they appear in the Cochrane review's small positive trials, with the caveats above.
Ashwagandha, maca and the rest
Herbal ingredients aren't covered here. They fall outside the Cochrane review's main conclusions and the trials above, and this page only reports what those cover rather than pretending to know more.
Food first
The contrast with diet is the point. A 2017 systematic review found diets rich in vegetables, fruit, fish, poultry, whole grains, nuts and low-fat dairy were consistently associated with better semen quality, and a 2020 study of 2,935 young Danish men found men eating most in a "prudent" pattern had total sperm counts 43 million higher than men eating least in it. Those are observational findings too, but they are large, consistent, and point to something with no downside.
What to do
- Spend the effort on food: oily fish, vegetables, fruit, nuts, legumes, and fewer sugary drinks and processed meats.
- If you take a supplement anyway, choose one plain product rather than a stack, and tell the doctor or clinic that ordered your semen analysis.
- Don't expect a test to move because of it. If it moves, the changes with stronger evidence in the main guide are the likelier reason.
- Skip anything marketed with a percentage improvement. The trials that could justify a number found none.
- If you are deficient in vitamin D or zinc on a blood test, correct it with your GP for its own sake.
Related guides
Sources
- de Ligny W, et al. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews, 2022.
- Smits RM, et al. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews, 2019.
- Steiner AZ, et al. The effect of antioxidants on male factor infertility: the Males, Antioxidants, and Infertility (MOXI) randomized clinical trial. Fertility and Sterility, 2020.
- Schisterman EF, et al. Effect of folic acid and zinc supplementation in men on semen quality and live birth among couples undergoing infertility treatment: the FAZST randomized clinical trial. JAMA, 2020 (NICHD summary).
- Lafuente R, et al. Coenzyme Q10 and male infertility: a meta-analysis. Journal of Assisted Reproduction and Genetics, 2013.
- Zhao J, et al. Zinc levels in seminal plasma and their correlation with male infertility: a systematic review and meta-analysis. Scientific Reports, 2016.
- Blomberg Jensen M, et al. Effects of vitamin D supplementation on semen quality, reproductive hormones, and live birth rate: a randomized clinical trial. Journal of Clinical Endocrinology and Metabolism, 2018.
- Jensen TK, et al. Associations of fish oil supplement use with testicular function in young men. JAMA Network Open, 2020.
- Salas-Huetos A, et al. Dietary patterns, foods and nutrients in male fertility parameters and fecundability: a systematic review of observational studies. Human Reproduction Update, 2017.
- Nassan FL, et al. Association of dietary patterns with testicular function in young Danish men. JAMA Network Open, 2020.