Mike Morden / Alamy
A man’s choice of underwear really can have an impact on his sperm, according to the largest study yet on the subject.
Jorge Chavarro and colleagues at Harvard University asked 656 men to provide a semen sample and blood sample, and answer a questionnaire about what type of underwear they wore most often in the previous three months.
Men who wore boxer shorts had a 25 per cent higher sperm concentration, 17 per cent higher total sperm count and 33 per cent more swimming sperm in a single ejaculate than men who wore other types of underwear.
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Those results are after adjusting for numerous other factors that might affect the results, such as differences in age, body mass index and smoking between the groups, but it’s impossible to rule out the possibility of other confounding factors that weren’t considered.
Sperm production is extremely sensitive to temperature, and requires temperatures a few degrees lower than the temperature inside the abdomen. Previous studies have shown that tight underwear can push the testes closer to the abdomen and raise the temperature inside the scrotum, says Chavarro.
Hormonal response
The researchers also measured the levels of reproductive hormones in the men’s blood, which showed that men who wore tight underwear had higher levels of follicle-stimulating hormone (FSH). This hormone is produced in the pituitary gland at the base of the brain, and stimulates sperm production.
“You would expect that if the testes are having difficulty producing sperm, the brain would produce more FSH and that’s exactly what we see,” says Chavarro.
Although the differences are quite significant, men who wear tight underwear typically still have sperm concentrations within the normal range and wouldn’t necessarily be expected to have difficulty conceiving children, says Chavarro. “The men who may benefit most from paying attention to what type of underwear they’re wearing are men who are already having problems with fertility.”
However, sperm production takes about three months from start to finish, so if a man changes his underwear, it may take that long for his sperm quality to improve.
Journal reference: Human Reproduction, DOI: 10.1093/humrep/dey259
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