Here's a summertime tale, based on the largest study of its kind, which should interest anyone who wants to have children. Men who wear boxer shorts have higher sperm counts than men who prefer tighter-fitting jockey shorts or briefs.

Sperm require a temperature slightly lower than body temperature to reach the best production level. That's why male testicles hang suspended in an exposed place, outside of the body. Similarly, boxer shorts keep testes cooler than tighter underwear does.

Men who usually wore tighter underwear also had higher concentrations of follicle stimulating hormone (FSH) in their blood, an indication that their bodies were trying to compensate for their decreased sperm production.

Researchers looked at semen samples from over 650 men who visited Massachusetts General Hospital for fertility treatments. In addition to taking blood and semen samples, they asked men what type of underwear they had worn most often during the previous three months.

Nearly half of the men in the study reported wearing boxers infrequently, but those who primarily wore boxer shorts had a 25 percent higher concentration of sperm compared to men who did not. Boxer-wearers also had a 17 percent higher total sperm count and 33 percent more sperm swimming. All three of these differences are statistically significant; and in each case researchers adjusted for other factors known to affect sperm, such as BMI, physical activity, smoking and even the number of hot baths a man took.

Men who tended to wear tighter underwear also had higher concentrations of follicle stimulating hormone (FSH) in their blood,. FSH is a hormone that increases sperm production and is an indication that their bodies were trying to compensate for their decreased sperm production by an alternate means.

The type of underwear men wore was self-reported and all the men in study had sought fertility treatment, so, the researchers say, these results might differ from those of the general public. But if you suspect you may have a fertility problem, switching away from whitey-tighties is a much simpler and far less expensive step than seeing a specialist. It's also a good idea for men who'd just like to be a little more comfortable below the belt.

There's no word on what health effects constantly wearing a suit and tie might have on the body.

The open-access article appears in Human Reproduction.