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 1300 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.
"Delaying fertility treatment for these couples so that they can make changes to their lifestyles, for which there is little evidence of effectiveness, is unlikely to improve their chances of a conception and, indeed, might be prejudicial for couples with little time left to lose."
The findings are published in the journal Human Reproduction. The researchers found that the proportion of men who had low numbers of swimming sperm was similar whether they had never been a smoker or were smoking more than 20 cigarettes a day.
Similarly, there was little evidence of any risk associated with alcohol consumption.
Infertility was most strongly linked with having had previous testicular surgery, being of black ethnicity or working in a manual occupation.
Professor Nicola Cherry, now at the University of Alberta, Canada, said: "The higher risk we found in manual workers is consistent with earlier findings that chemicals at work could affect sperm and that men should continue to keep work exposures as low as possible."
- Independent
BELOW THE BELT
Harmful
Tight Y-fronts
Not so harmful
Alcohol, drugs, smoking, obesity.
