"Beyond providing additional evidence that underwear choices may impact fertility, our study provides evidence, for the first time, that a seemingly random lifestyle choice could have profound impacts on hormone production in men at both the level of the testis and the brain", Jorge Chavarro, one of the study's authors and an associate professor of nutrition and epidemiology at Harvard, said in a statement.
The study was published August 8 in the journal Human Reproduction.
The study included men who visited the Massachusetts General Hospital for fertility problems.
Harvard University researchers have done the most comprehensive study to date into the effect of underwear on sperm quality and found that the tighter the garment the lower the sperm count and concentration.
The levels of follicle-stimulating hormone or FSH was found to be higher among men who wore briefs regularly.
FSH promotes sperm production. This proven link between temperature and fertility is often the linchpin of pro-boxer arguments presented during debates with briefs wearers.
Chavarro told New Scientist that, although men who wear tight underwear have a lower sperm count, they generally still have sperm concentrations that fit in the average range.
Wearing looser underpants could be a simple way for men to improve their sperm count and the hormones that control it, a USA study suggests.
They also had 17 percent higher sperm count and 33 percent more swimming sperm in a single ejaculate. "Were it not for the higher FSH levels, their sperm count would probably be even lower", Chavarro said. "Additionally, the differences in hormone and semen analysis parameters were not different enough to be identified as the primary cause of infertility".
Firty-three percent of the men said they usually wore boxers. This study adds to the scientific basis to that advice.
More than half (345) wore boxer shorts, and only a slightly smaller number of the group wore snugger-fitting underwear: 311.
"These results point to a relatively easy change that men can make when they and their partners are seeking to become pregnant", Lidia Mínguez-Alarcón, the study's lead author and a researcher at the Harvard T.H. Chan School of Public Health, said in a press release.
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