Male fertility has fallen sharply over the past half-century. A 2017 meta-analysis in Human Reproduction Update, one of the largest of its kind, found that sperm concentration dropped by more than 50% among men in Western countries between 1973 and 2011.
Diet, lifestyle, and environmental factors all play a role. For men looking to take targeted action, certain supplements have a meaningful evidence base behind them. Others are largely unproven, despite heavy marketing.
This guide covers the nutrients most supported by current research, what doses have been studied, and what the evidence actually says, including where it falls short.
Can supplements actually improve male fertility?
The short answer is: for semen parameters, often yes. For pregnancy outcomes, the picture is more mixed.
What research consistently shows is that men with deficiencies in certain nutrients tend to have lower sperm count, reduced motility, or poorer morphology. Addressing those deficiencies can produce measurable improvements in sperm quality. Whether that translates directly to higher pregnancy rates is harder to demonstrate, partly because fertility involves two partners and many variables.
Supplements work best alongside lifestyle changes and a proper semen analysis, not instead of them. More on that at the end of this article.
NAC (N-acetyl cysteine)
NAC is one of the best-evidenced male fertility supplements and one of the most under-discussed.
Oxidative stress is estimated to contribute to 30–80% of male infertility cases. Sperm are particularly vulnerable to reactive oxygen species (ROS) because they have limited antioxidant defences of their own. NAC addresses this directly: it’s a precursor to glutathione, the body’s primary antioxidant, which protects sperm from oxidative damage to their DNA and membrane.
A 2021 meta-analysis pooling three randomised controlled trials (n=431) found that NAC supplementation produced a statistically significant increase in sperm motility of approximately 5% and sperm concentration of around 4 million per millilitre compared to placebo. A 2019 RCT in men with asthenoteratozoospermia (poor motility and morphology) showed significant improvements across count, motility, and morphology. Separately, a trial involving men post-varicocelectomy reported a pregnancy rate of 33% in the NAC group versus 10% in controls.
NAC has also been shown to reduce sperm DNA fragmentation — a marker that doesn’t always show up in a standard semen analysis but matters significantly for embryo development.
Typical dose studied: 600mg daily for a minimum of three months.
Epsilon Life’s NAC+ 600mg capsules are vegan, UK-manufactured, and match the dose used across this research. You can read more about NAC’s broader health benefits here.
Vitamin D
Vitamin D receptors are found in testicular tissue, and the vitamin plays a direct role in testosterone synthesis and sperm maturation.
A 2023 meta-analysis across five trials (n=648) found an average improvement of approximately 5% in sperm motility in men supplementing with around 4,000 IU daily. Earlier research published in Human Reproduction (2011) found that men with sufficient vitamin D levels had significantly higher sperm motility than those who were deficient. The key qualifier in most of this research: the benefits are most pronounced in men who are actually deficient to begin with.
In the UK, low vitamin D is common year-round and near-universal in winter. Public Health England recommends supplementation for most adults between October and March. If you’re unsure of your levels, a simple blood test through your GP or a private lab will confirm.
Typical dose studied: 2,000–4,000 IU daily, particularly where deficiency is confirmed.
Epsilon Life’s Vitamin D3K2 combines D3 with K2, zinc, and boron in an MCT oil base for improved absorption. K2 helps direct calcium appropriately and is the recommended co-factor for D3 supplementation. This formula also contains zinc, which has its own well-documented role in male fertility, covered below.
Zinc
Zinc is essential for testosterone production, sperm formation, and the structural integrity of sperm DNA. Seminal zinc levels are consistently lower in men with poor fertility, and supplementation has shown positive effects across multiple semen parameters.
A review in the Journal of Reproduction & Infertility (2018) found associations between low zinc and reduced sperm count and motility. Combinations of zinc with other nutrients, particularly over 12 or more weeks, have shown improvements in sperm concentration in more recent trials.
One important caveat from the research: very high doses (trials using upwards of 220mg elemental zinc) have in some cases been associated with increased DNA fragmentation. The evidence-based range for supplementation is 15–40mg of elemental zinc per day, which is well within normal product doses.
Good dietary sources include red meat, shellfish, pumpkin seeds, and legumes. If you’re supplementing, zinc is included in Epsilon Life’s D3K2 formula at a sensible dose alongside vitamin D and K2.
Magnesium
Magnesium doesn’t appear in many fertility supplement conversations, but there’s reasonable evidence it belongs there.
It’s involved in testosterone regulation and has been shown to influence sperm motility directly. Research published in Biological Trace Element Research found magnesium levels were significantly lower in infertile men compared to fertile controls. Separate research showed magnesium supplementation raised testosterone levels in both athletes and sedentary men over four weeks.
Deficiency is common in the UK. Many men fall short of the recommended 300mg per day through diet alone, particularly with a low-vegetable diet or regular alcohol consumption.
Magnesium glycinate is one of the more bioavailable forms: better absorbed than oxide and gentler on the stomach than citrate at higher doses.
What about CoQ10?
CoQ10 is one of the better-evidenced supplements we don’t currently stock, so it’s worth an honest mention.
Coenzyme Q10 is an antioxidant concentrated in sperm mitochondria, where it supports energy production and motility. A 2024 review identified it as a standout nutrient for sperm concentration and motility, with one meta-analysis reporting an odds ratio of 6.02 for pregnancy in supplemented men. If you’re considering CoQ10 separately, look for the ubiquinol form (the active, more bioavailable version) rather than standard ubiquinone.
Lifestyle factors that support supplement effectiveness
No supplement replaces the basics. The research is consistent: lifestyle changes produce some of the strongest fertility outcomes, and supplements work best when built on top of them.
- Weight. A 5–10% reduction in body weight is associated with a 20–30% improvement in pregnancy odds in men who are overweight. Excess body fat raises oestrogen levels and reduces testosterone.
- Exercise. Around 150 minutes of moderate exercise per week is associated with better semen parameters. Overtraining raises cortisol and can suppress testosterone, so more isn’t better.
- Smoking. Smoking reduces sperm motility by approximately 20% and damages sperm DNA. The effect is dose-dependent and largely reversible after cessation.
- Alcohol. Even moderate drinking affects motility in some studies. Reducing intake for the 90-day supplement period is worthwhile.
- Sleep. Testosterone production peaks during deep sleep. Consistently sleeping fewer than 6 hours per night is associated with reduced testosterone and impaired sperm quality.
- Heat exposure. Sperm production is temperature-sensitive. Frequent saunas, hot baths, or tight clothing can temporarily reduce sperm count.
A practical approach: get a baseline semen analysis first. It takes the guesswork out of which parameters need the most attention, and gives you something to compare against after 90 days of consistent supplementation and lifestyle changes.
Frequently asked questions
What are the best supplements for male fertility?
The best-evidenced options are NAC, vitamin D (particularly if you’re deficient), zinc, and magnesium. Each addresses a different mechanism: antioxidant protection, hormone synthesis, sperm formation, and motility. Getting a baseline semen analysis before starting any supplement programme helps you prioritise more accurately.
How long do male fertility supplements take to work?
Sperm take roughly 74 days to mature (spermatogenesis). Most supplement trials run for three months for this reason. Don’t expect changes in the first few weeks; consistent use over a full sperm cycle is the minimum timeframe for meaningful results.
Can NAC improve sperm count?
Research suggests it can. A 2021 meta-analysis of three RCTs found significant improvements in sperm motility and concentration in men taking 600mg of NAC daily. NAC works primarily by reducing oxidative stress, which is estimated to contribute to 30–80% of male infertility cases. It also appears to reduce sperm DNA fragmentation, which isn’t captured in a standard semen analysis but matters for embryo development.
Is vitamin D important for male fertility?
Yes, particularly if you’re deficient. Vitamin D receptors are present in testicular tissue, and deficiency is consistently linked to lower testosterone and reduced sperm motility. A 2023 meta-analysis found approximately 5% improvement in motility with supplementation at around 4,000 IU. Given how common vitamin D deficiency is in the UK, it’s one of the most practical supplements for most men to consider.
Is it better to take individual supplements or a male fertility multivitamin?
Fertility-branded multivitamins often contain the right ingredients but at lower doses than those used in clinical research. Individual supplements allow better control over dosage. A product that combines several key nutrients, such as D3K2 with zinc included, can cover multiple bases efficiently without taking a large number of separate capsules.
References
- Levine H, et al. (2017). Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update, 23(6), 646–659. doi:10.1093/humupd/dmx022
- Jannatifar R, et al. (2019). Effects of N-acetyl-cysteine supplementation on sperm quality, chromatin integrity and level of oxidative stress in infertile men. Reproductive Biology and Endocrinology. PMC6377938
- Ahmadi S, et al. (2021). Meta-analysis of NAC supplementation and sperm parameters. Referenced in Frontiers in Endocrinology review. Frontiers in Endocrinology
- Blomberg Jensen M, et al. (2011). Vitamin D receptor and vitamin D metabolizing enzymes are expressed in the human male reproductive tract. Human Reproduction, 26(5), 1303–1317. PubMed
- Fallah A, et al. (2018). Zinc is an essential element for male fertility. Journal of Reproduction & Infertility, 19(2), 69–81. PMC
- Cinar V, et al. (2011). Effects of magnesium supplementation on testosterone levels. Biological Trace Element Research, 140(1), 18–23. PubMed
- Gabrielsen JS, Lamb DJ. (2024). Antioxidants and male fertility. PMC. PMC11756326
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. If you have concerns about your fertility, speak to your GP or a registered healthcare professional. Supplements may interact with medications, so always check with a pharmacist or doctor before starting a new supplement regimen.
