Tight Underwear Is Linked To Lower Sperm Quality

For years, men have heard that if they’re trying to conceive, they should stop wearing tight-fitting underwear, and let loose, so to speak, with boxers. It’s been thought that temperature was the reason that testicles, and therefore sperm, may be in better shape with loose-fitting underwear, but the scientific evidence has been slightly mixed. A new study from the Harvard T.H. Chan School of Public Health goes further in showing that underwear choice does seem to be linked to sperm quality—and it also shows what mechanisms might underlie the connection.

The study was published this week in the journal Human Reproduction.

The researchers recruited over 650 men who along with their partners were seeking fertility treatment at Massachusetts General Hospital. The men provided semen and blood samples, so the team could look not only at sperm quantity and quality, including DNA damage, but also at hormone levels. The men also answered questions about their diets, exercise and other lifestyle variables, as well as what type of underwear they wore.

The team of course was interested in correlations between underwear type, sperm quality/quantity, and any underlying hormonal differences that might explain the connections.

Men who mostly wore boxer shorts had 25% higher concentration of sperm, 17% higher total sperm count, and 33% more swimming sperm in one ejaculation, relative to men who wore tighter forms of underwear (“tighty-whities,” bikini briefs, etc.). There was also a trend toward more sperm being correctly shaped, although this result was not statistically significant, meaning it could have been due to chance. The team didn’t find any differences in DNA quality of the sperm between the various types of underwear.

Interestingly, and what the new study really brings to the table, the men who wore boxers had 14% lower levels of a sex hormone called follicle stimulating hormone (FSH). As the name suggests, this hormone stimulates the cells that produce sperm. The authors suggest that what’s going on is a compensatory mechanism, meaning that when a man’s sperm production machinery is injured by the heat caused by tight underwear, their brains respond by signaling the production of more FSH to try to correct the situation. This could explain why despite having poorer sperm quality, they have higher levels of this particular sex hormone.

“These findings are consistent with the presence of a compensatory increase in [sex hormone] secretion secondary to testicular injury due to elevated scrotal temperatures caused by wearing tight underwear,” the authors write in their paper.

The results held strong even after adjusting for variables that might affect sperm quality, including BMI, exercise, how often the men took hot baths and Jacuzzis, and smoking. But the study is still just a correlation, and can’t illustrate causation—it’s also not clear whether or how much sperm quality translates into pregnancy rates. Finally, the authors point out that other factors could affect testicular temperature, like the type of pants worn and the fabric of pants or underwear.

More work will be needed to understand exactly how the cascade occurs, and how reversible it might be. But in the meantime, this is the largest study to date on the connection between underwear choice and sperm quality. Underwear certainly isn’t the only variable that affects conception, but if you’re trying to conceive, it may be worth it to pay attention to the study's message—and change your underwear.

Source: https://www.forbes.com/sites/alicegwalton/2018/08/09/tight-underwear-is-linked-to-lower-sperm-quality-new-study-hints-at-why/#2fa3fc4c4d04