Lifestyle factors that affect male fertility: a practical guide

The lifestyle factors with the most consistent links to poorer sperm are smoking, excess body weight, regular heavy drinking, frequent cannabis use, anabolic steroids and keeping the testes too warm. Sleep, activity and diet matter too, though the evidence is weaker. Most of these are within your control, and because sperm take around two months to develop¹, changes need about three months to show.

Which lifestyle factors affect male fertility most?

The strongest and most consistent evidence is for smoking, obesity and anabolic steroids, followed by regular heavy drinking and frequent cannabis use. Heat exposure, sleep, physical activity and diet also show links, but mostly from observational studies that cannot prove cause and effect.

Infertility affects around 15% of couples of reproductive age, and male factors, including poorer semen quality, are thought to be responsible for around a quarter of those cases². Yet fertility advice is still aimed mostly at women. That is a missed opportunity, because many of the things that drag down sperm count and quality are habits rather than fixed traits.

A word on the kind of evidence you'll see below. Most lifestyle research on sperm is observational: researchers compare men with different habits and look at their semen. That can show a link but not prove the habit caused it, because men who smoke, drink heavily or sleep badly often differ in other ways too. Where there is trial evidence, as with weight loss, it is flagged. The table summarises the headline findings.

Sources: Sharma 2016; Sermondade 2013; Andersen 2022; Jensen 2014; Gundersen 2015; Sheynkin 2005; Jensen 2013; Gaskins 2015.

Does body weight affect sperm count?

Yes. A meta-analysis of 13,077 men found that obesity raised the odds of a low or zero sperm count, and the risk roughly doubled in men with severe obesity³. In a randomised trial substudy, men with obesity who lost weight saw their sperm concentration rise by about half⁴.

The meta-analysis pooled 21 studies of men from the general population and from fertility clinics³. Compared with men of normal weight, the odds of a low (oligozoospermia) or zero (azoospermia) sperm count were 1.11 times higher in overweight men, 1.28 times higher in men with obesity and 2.04 times higher in men with severe obesity. Underweight men also had slightly raised odds, though that result was not statistically clear. The relationship was J-shaped: both ends of the scale carried more risk than the middle.

The more hopeful finding is that the effect appears reversible. In a Danish trial, 56 men with obesity followed an eight-week low-calorie diet and lost 16.5 kg on average⁴. Sperm concentration rose 1.49-fold and total sperm count 1.41-fold. Crucially, the improvement lasted a year in men who kept the weight off, but not in men who regained it.

That was a very low-calorie diet under medical supervision, not something to try alone. The practical lesson is simpler: steady, sustainable weight loss is one of the few lifestyle changes with trial evidence behind it, and keeping it off is what protects the gain.

Does smoking or cannabis affect sperm?

Yes. A meta-analysis of 5,865 men linked cigarette smoking to lower sperm count, motility and normal shape, with bigger effects in moderate and heavy smokers⁵. Smoking cannabis more than once a week was linked to a 28% lower sperm concentration⁶.

The smoking meta-analysis pooled 20 studies and found average reductions in sperm concentration of about 9.7 million per mL, in motility of about 3.5 percentage points and in normal morphology of about 1.4 points⁵. Those averages may sound modest, but the effect was larger in infertile men than in the general population, which is exactly the group that can least afford a further drop.

Cannabis is often assumed to be the gentler option. In a study of 1,215 young Danish men, 45% had used it in the previous three months⁶. Those who smoked it more than once a week had 28% lower sperm concentration and 29% lower total sperm count after adjusting for other factors. Men who combined weekly cannabis with other recreational drugs had 52% lower sperm concentration.

The research on vaping is much thinner than for cigarettes. Until it catches up, the cautious approach while trying to conceive is to stop nicotine and cannabis in all forms rather than switch between them.

How much alcohol affects male fertility?

Regular drinking matters more than the occasional big night. In a study of 1,221 young men, sperm quality fell as typical weekly intake rose, with the clearest effects above 25 units a week; men drinking more than 40 units had 33% lower sperm concentration than those drinking 1 to 5⁷.

The researchers looked at three patterns: drinking in the week before the test, drinking in a typical week and binge drinking over the previous month⁷. Sperm concentration, total count and the share of normally shaped sperm all fell as typical weekly intake rose. The link appeared from about 5 units a week but was strongest above 25. Binge drinking on its own was not independently linked to semen quality once habitual intake was accounted for.

Alcohol was also linked to changes in testosterone and SHBG levels⁷. The authors' conclusion was blunt: young men should be advised to avoid habitual alcohol intake. For anyone trying to conceive, keeping drinking low and occasional rather than daily is a reasonable target.

Do laptops, hot baths and saunas harm sperm?

Heat is a recognised risk to sperm production, and everyday habits can warm the testes measurably. In one experiment, an hour with a working laptop on the lap raised scrotal temperature by about 2.6 to 2.8 °C⁸.

Sperm production runs best when the testes are a little cooler than the rest of the body. The laptop study measured scrotal temperature in 29 healthy volunteers for an hour in two sessions: once with a working laptop on the lap and once sitting in the same position without it⁸. Temperature rose in both, by about 2.1 °C just from sitting with the thighs together, but significantly more with the laptop. The study measured temperature rather than sperm, so it can't say how much sperm quality suffers, but its authors flagged repeated heating as a possible risk.

The same logic applies to long hot baths, hot tubs, saunas, heated car seats and long periods sitting. None of these needs banning for life, but if you're trying to conceive, reducing them for a few months is an easy, free change. We look at how long heat effects take to clear in how long it takes sperm to regenerate.

Do exercise, sleep and steroids affect fertility?

Yes, in different directions. More activity and less sitting were linked to higher sperm counts⁹, severe sleep disturbance to lower ones¹⁰, and anabolic steroids can suppress fertility for months after stopping¹¹.

Exercise and sitting

In a study of 189 young men, those doing 15 or more hours a week of moderate to vigorous exercise had 73% higher sperm concentration than men doing less than 5 hours⁹. Men watching more than 20 hours of TV a week had 44% lower concentration than men watching none. Neither habit was linked to motility or shape. It is a small observational study, but it points the same way as the weight evidence: move more, sit less.

Sleep

Among 953 young Danish men, those with high levels of sleep disturbance had 29% lower sperm concentration than men with low levels¹⁰. The pattern was an inverted U, so the relationship is not simple, and the authors called for studies testing whether better sleep improves semen. Poor sleep also often travels with stress, long shifts and drinking. For more on the wider picture, see sleep and sex drive.

Anabolic steroids and testosterone

This is the lifestyle factor most likely to be overlooked in the gym. Taking testosterone or other anabolic steroids switches off the hormonal signals that drive sperm production. A systematic review found that during steroid use, LH, FSH and the body's own testosterone all fell significantly; after stopping, LH and FSH took 13 to 24 weeks to return to baseline, and testosterone was still low at 16 weeks¹¹. Users also showed sperm changes, smaller testes and subfertility. Prescribed testosterone replacement therapy has the same effect on sperm, so raise fertility plans with the prescriber before starting.

What should you eat to improve sperm quality?

A generally healthy diet is linked to better semen quality. A systematic review of observational studies found that diets rich in fish, poultry, cereals, vegetables, fruit and low-fat dairy were linked to better sperm, while processed meat, full-fat dairy, sugary drinks and sweets were linked to worse².

The review screened 1,944 articles and included 35 higher-quality observational studies². Diets rich in omega-3 fats, antioxidant nutrients such as vitamins C and E, selenium, zinc and lycopene, plus vitamin D and folate, and low in saturated and trans fats, were associated with better semen quality. On the negative side, processed meat, soy foods, potatoes, full-fat dairy, cheese, coffee, alcohol, sugar-sweetened drinks and sweets were detrimentally associated with semen quality in some studies.

Two caveats. First, these are associations: men who eat plenty of fish and vegetables probably differ from men who don't in many ways. Second, these studies looked at food, not pills. Many of the same nutrients are also sold as supplements, and trials of individual ingredients have been run separately; we cover what they found in supplement ingredients for men's sexual health.

How long do lifestyle changes take to improve fertility?

About three months. Sperm take roughly 64 days to develop¹ plus a few days to mature, so the sperm in today's sample reflect your habits from two to three months ago. In the weight-loss trial, gains were seen after eight weeks⁴.

That lag is the most useful thing to understand about male fertility and lifestyle. It means a single good week won't show up, and one bad weekend is unlikely to undo months of effort. It also means the best time to start is before you begin trying to conceive, not after months of disappointment.

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This article is for education and is not medical advice. It has not been reviewed by a doctor. If you have symptoms or concerns, see a GP.