Tight pants are the Y-frontrunner in male fertility problems
Men trying to improve their sperm count can ditch the healthy living advice but should think carefully about their underwear, doctors have found.
Smoking, drinking alcohol, using recreational drugs and being overweight are all listed in British National Institute of Clinical Excellence guidelines as factors likely to harm male fertility.
But research has found they make little difference -- with one exception. Changing underwear style could improve a man's chances of having a baby.
"There is no need for men to become monks just because they want to be a dad," said Allan Pacey, lecturer in andrology at the University of Sheffield, who was involved in the study.
"But if they are a fan of tight Y-fronts, then switching underpants to something a bit looser for a few months might be a good idea."
To make healthy sperm, the testicles need to be a degree or two below body temperature, which is why evolution has seen to it that they hang outside in their own sac, where it's cooler.
Tight Y-fronts risk reversing what millions of years of evolution have achieved.
The researchers from the Universities of Manchester and Sheffield compared some 900 men with low sperm counts with 1,300 who had high sperm counts.
They found drugs, tobacco, alcohol and weight had little effect. But boxer shorts did. Dr Andrew Povey, from the University of Manchester's School of Community-based Medicine, said: "This 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."
The findings are published in the journal Human Reproduction.