There's more work to be done but experts suggest ditching the tight underwear while trying to conceive.
When it comes to underwear, different men have different preferences, but when it comes to sperm health, the boxer short is best.
This comes from a new study out of Harvard this week. According to the author of the study published in the journal Human Reproduction, briefs really can lead to hot temperatures that can lower sperm counts. Sorry, brief lovers.
Researchers looked at the sperm counts of more than 600 men who went to the Massachusetts General Hospital with their partners between 2000 and 2017 for help with fertility. The men also answered questions about their lifestyle choices, including which sort of underwear they prefer.
If you feel like you've heard about underwear preferences impacting fertility before, you're not having deja vu. As CNN reports, study author Lidia Mínguez-Alarcón of Harvard's T.H. Chan School of Public Health says "whether underwear choice affects sperm production has been a topic of research for several years," but this study is the first to look past the heat factor and into things like how briefs and boxers impact reproductive hormones and DNA fragmentation.
Dr. Jorge Chavarro, associate professor of nutrition and epidemiology at Harvard and another of the study's authors told NBC News the study "confirms previous smaller-scale studies with a larger study."
According to the researchers, men who wore tight underwear had higher levels of follicle-stimulating hormone meant to increase sperm production. Meanwhile, "guys who wear boxers had higher sperm concentration than men who wore more tightly fitting underwear," says Chavarro.
According to CNN, researchers who've been looking at the relationship between underwear and sperm for years say it's important to note that this was a study of sperm quality, not fertility because there is a big difference in measuring the two.
However, some of the folks who've spent their careers deep in the boxers versus briefs debate say potential dads should just go ahead and make the switch to looser briefs.
"This study confirms my long-held belief that men with poor sperm quality could potentially improve things by wearing looser underwear and keeping their testicles as cool as possible," Professor Allan Pacey of the at the University of Sheffield told Science Media Centre.
He says the new results confirm his own 2012 study on the subject.
Another expert, Professor Richard Sharpe of the University of Edinburgh, thinks next time researchers should also look at the "occupation of the men and the time that they spend seated... as it is established that modern sedentary lifestyles/occupation are associated, like wearing of tight underwear, with increase in scrotal temperature," he says. "It might be predicted that men who spend much of their day seated and also wear tight underwear would be most likely to suffer a fall in their sperm production due to scrotal heating."
Mínguez-Alarcón, too, wants more info than her study gathered. She suggests scientists need to know more than just whether a man sports boxers of briefs, they should also be considering the fabric of the undies, as well as what kind of pants he wears.
Future studies may look at that, but in the meantime, CNN reports Mínguez-Alarcón offers one useful piece of advice: "Men could improve their sperm production by easily changing their type of underwear worn to boxers."