Sperm health and the lifestyle factors with measured effects

This page takes the lifestyle factors most often linked to sperm health one at a time, and grades the evidence for each in plain terms. Consistent means several studies, pooled in a meta-analysis, point the same way. Mixed means pooled studies disagree, or find an effect only at high exposure. Limited means the evidence is sparse, small or indirect. Nearly all of it is observational, comparing men with and without a habit, so it shows an association rather than proof that changing the habit changes the result. The World Health Organization names smoking, excessive alcohol and obesity among the lifestyle factors that can affect fertility (WHO, Infertility fact sheet, 2025). What counts as a low sperm count, and what usually happens next, is in its own guide.

Smoking is linked to lower sperm count, motility and normal forms

Evidence: consistent. A meta-analysis of 20 studies and 5,865 men found that smokers had a sperm concentration about 9.7 million per mL lower than non-smokers, with lower motility and fewer normally shaped sperm. The effect was larger in moderate and heavy smokers than in light smokers, and larger in infertile men than in men from the general population (Sharma and colleagues, European Urology, 2016).

Obesity is linked to a higher chance of a low sperm count

Evidence: consistent, for the association. A meta-analysis of 21 studies and 13,077 men compared the odds of a low sperm count or no sperm with those of men of normal weight. The odds were about 11% higher in overweight men, 28% higher in men with obesity and roughly twice as high in men with severe obesity (Sermondade and colleagues, Human Reproduction Update, 2013). The authors noted that whether reaching a normal weight improves sperm results had yet to be tested.

Heavy drinking, rather than occasional drinking, is linked to poorer semen

Evidence: mixed. A meta-analysis of 15 cross-sectional studies and 16,395 men found lower semen volume and fewer normally shaped sperm in men who drank. The difference was clearest between daily and occasional drinkers, and the authors concluded that moderate drinking did not appear to harm semen quality; the only advice they considered supported was to avoid heavy drinking (Ricci and colleagues, Reproductive BioMedicine Online, 2017). The NHS advises men with a low sperm count to drink no more than 14 units a week, spread over three or more days (NHS, Low sperm count, 2024).

Anabolic steroids and testosterone therapy suppress sperm production

Evidence: consistent, with a known mechanism. Testosterone from outside the body lowers FSH and LH, the pituitary hormones that drive sperm production. StatPearls (2026) states that testosterone therapy suppresses sperm production even when it is prescribed correctly for a confirmed condition, and that recovery after stopping can take up to two years. The WHO (2025) lists anabolic steroid use among the causes of abnormal semen results, and the NHS names anabolic steroids among the drugs that men with a low sperm count are advised to avoid (2024).

Heat, cannabis and chemicals at work rest on weaker evidence

Evidence: limited.

• Heat. The NHS states that higher scrotal temperature is linked to poorer semen quality, but that it is uncertain whether loose-fitting underwear makes a difference to fertility (NHS, Infertility: causes, 2023). Its page on low sperm count still lists loose underwear among the steps that may help (2024).
• Cannabis and other drugs. StatPearls (2026) lists stopping cannabis among the changes encouraged in men with infertility, and the NHS names cocaine among the drugs to avoid (2024). Neither source gives a size for the effect of cannabis.
• Chemicals at work. The NHS lists pesticides, solvents and some heavy metals as workplace exposures to avoid (2024), and the CDC notes that toxic substances at home and at work can harm the reproductive systems of both men and women (CDC, Planning for pregnancy, 2025).

Supplement trials have not shown better semen or more births

Evidence: randomized trials, which found no benefit. Supplements sold for male fertility often contain folic acid, zinc and antioxidants. Two large US trials tested them against a placebo:

• In the Folic Acid and Zinc Supplementation Trial, 2,370 men in couples planning fertility treatment took folic acid and zinc or a placebo daily for six months. Live birth rates were 34% and 35%, most semen measures did not differ, and DNA damage in sperm was slightly higher in the supplement group (Schisterman and colleagues, JAMA, 2020).
• In the Males, Antioxidants, and Infertility trial, 174 men with abnormal semen results took an antioxidant combination or a placebo. The antioxidants did not improve semen measures or sperm DNA, and live birth rates did not differ between the groups (Steiner and colleagues, Fertility and Sterility, 2020).

StatPearls (2026) notes that published guidelines do not recommend supplements, vitamins or nutraceuticals for male infertility, because the studies behind them are too weak to establish that they work.

UK and US sources give the same practical list

The NHS list for men with a low sperm count covers drinking within 14 units a week, losing weight if overweight, stopping smoking, wearing loose underwear, avoiding chemicals at work, and avoiding recreational drugs such as anabolic steroids and cocaine (NHS, 2024). In the US, the American College of Obstetricians and Gynecologists advises male partners to give up smoking, alcohol and drugs before a couple tries to conceive, because these may damage sperm (ACOG, Good Health Before Pregnancy, reviewed 2025). The studies above were not designed to show whether these changes shorten the time to pregnancy, and their authors call for that research.

What the measures on a report mean is explained in the guide to semen analysis. Causes of male infertility beyond lifestyle are covered in the guide to male fertility.