An unhealthy lifestyle may not affect sperm quality as much as previously thought.
A study in the journal Human Reproduction indicates that smoking, high alcohol consumption and being overweight have little effect on semen quality. Wearing tighter underpants, on the other hand, did reduce levels of swimming sperm, a strong indicator of male fertility.
Researchers asked 2,249 men at 14 UK fertility clinics to fill in detailed questionnaires about their lifestyle. They compared the answers of the 939 men with low sperm quality with the 1,310 men with normal sperm and found that even a 20-a-day smoking habit did not significantly affect swimming sperm levels.
Study leader Dr Andrew Povey at the University of Manchester emphasised that lifestyle choices were 'important for other aspects of our health' but said that the research 'potentially overturns much of the current advice given to men about how they might improve their fertility and suggests that many common lifestyle risks may not be as important as we previously thought'.
Current advice from the National Institute for Health and Clinical Excellence (NICE) suggests doctors should warn men of the negative impact of smoking and drinking on sperm quality. Fertility treatment is sometimes delayed so couples can alter their lifestyles.
Dr Povey said that the study suggested that such a delay 'is unlikely to improve [couples'] chances of conception and, indeed, might be prejudicial for couples with little time left to lose'.
A NICE spokesperson told the BBC that 'the draft update of our fertility guideline is currently open for consultation. However, until the update of this guideline is published later this year, the NHS should continue to follow the recommendations in the current fertility guideline'.
Study co-author Dr Allan Pacey, from the University of Sheffield, said that lifestyle factors may affect other aspects of sperm quality - such as the size and shape of the sperm - not measured in the study. He said it was therefore 'important that men continue to follow sensible health advice and watch their weight, stop smoking and drink alcohol within sensible limits. But there is no need for them to become monks just because they want to be a dad'.
On the finding that tighter underwear did slightly impact levels of swimming sperm, he said that if a man trying for a baby was 'a fan of tight Y-fronts, then switching underpants to something a bit looser for a few months might be a good idea'.