Chavarro said that men who chose to wear boxers were found to have a higher concentration of sperm compared to those who wore tight underwear. This study has the largest sample size yet, including 656 male partners of couples seeking treatment at the fertility center of Massachusetts General Hospital in Boston.
The men, who were between the ages of 32 and 39, completed a survey that included questions about the style of underwear they wore in the previous three months.
Men who primarily wore boxer shorts had a 25 per cent higher sperm concentration, a 17 per cent higher total sperm count and 33 per cent more swimming sperm in a single ejaculation than people with tighter trousers, the study found.
It's been suggested that 21st Century man is, reproductively speaking, only half the man his grandfather was.
"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", he said.
Study participants were asked whether they wore boxers, jockeys, bikini, briefs or "other".
The study was published August 8 in the journal Human Reproduction. "There seems some compensation, but this compensation is not sufficient to bring them back to sperm counts of men who wear looser-fitting underwear".
Results showed that men who preferred boxers had a 25 percent higher sperm concentration and a 17 percent higher sperm count.
Dr. Jorge Chavarro, associate professor of nutrition and epidemiology at Harvard, lead author of the study has explained that tight underwear in men such as briefs can raise the scrotal temperatures and this can contribute to a lower sperm count and infertility.
The researchers also noted that the men who wore boxers had 14 percent lower levels of follicle stimulating hormone, compared with men who didn't.
"However, I think it is a reasonable low cost and low risk lifestyle change that men with poor sperm quality can undertake to potentially improve their semen quality", Prof Pacey said. In that, the decreased sperm production among men in tighter underwear signals the brain to boost production of hormones that stimulate the activity of the gonads to try to increase sperm production.