Men should go commando – or at least wear boxers – before they start a family as wearing tighter pants really does damage a man’s fertility, a new study found.
Those with looser-fitting underwear produced up to a third more swimming sperm than those who preferred budgie-smuggler type briefs.
The groundbreaking study is the largest of its kind to look into the truth of a long-held suspicion that tighter pants such as Y-fronts or briefs affect a man’s ability to father children.
Previous studies have been inconclusive as to whether a tighter option increases scrotum temperature and so reduces sperm quality and numbers.
The study found men who wear boxer shorts have higher sperm concentrations than men who wear tighter fitting underwear including very skimpy briefs dubbed a bikini.
Men who wear pants had higher levels of a hormone that stimulates sperm production which suggested it kicks into gear to compensate for testicular damage from higher temperatures and decreasing sperm counts and concentration.
But Harvard University scientists said as no study participants went commando, they could only assume it would be good for sperm production.
Co-author Associate Professor Dr Jorge Chavarro at the Harvard T.H. Chan School of Public Health said: “We didn’t have enough men in the study who wore no underwear to be able to make any meaningful comparisons.
“In theory, their sperm production will likely be comparable to that of men wearing boxers but in the absence of data we cannot tell for sure.
“I do not use boxers but I’ll leave the specifics of my underwear to my wife and myself. We have two lovely girls.
“I have to say, though, that had I been working on male factor infertility when my wife and I were trying for a baby, I would have probably bought a few boxers.”
The study found underwear choice could actually be a ‘key regulator’ of sexual development and reproduction.
Boxer-shorts wearers had a 25 per cent higher sperm concentration than those wearing briefs.
Their sperm count was also 17 per cent higher and a single ejaculation contained 33 per cent more swimming sperm.
But the team admitted they did not take into account what type of trousers the participants wore.
Wearing skinny jeans or a certain type of underwear fabric could also skew the results, the study says.
Published in the journal Human Reproduction, the study analysed semen and blood samples from 656 men between the ages of 18 and 56.
Each participant also answered a questionnaire about the style of underwear they wore most frequently in the preceding three months.
Options included boxers, jockeys (underwear that finishes just above the knee), briefs. bikini (very brief briefs) and other.
Over half – 53 per cent – usually wore boxers.
Lead author Research Scientist Dr Lidia Mínguez-Alarcón said: “These results point to a relatively easy change that men can make when they and their partners are seeking to become pregnant.”
Blood samples of 304 of the men were analysed and showed men who wore boxers had 14 per cent lower levels of follicle stimulating hormone (FSH) compared with men who didn’t wear boxers.
FSH is known to play an important role in male fertility.
The simultaneous presence of lower sperm counts and higher FSH among men wearing tight-fitting underwear suggested the presence of a compensatory mechanism whereby 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.
Prof Chavarro added: “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.”
Dr Mínguez-Alarcón said: “An important strength of this study is that we were able to investigate the potential relationship between the type of underwear worn and indicators of testicular function such as reproductive hormone levels and DNA damage, which were missing in all previous studies on the topic.
“Because of this, we were able to find a potential compensatory mechanism whereby decreased sperm production relating to the type of underwear signals to the hypothalamus to increase secretion of gonadotropin, a hormone that acts on the testes and that is reflected by the increased levels of FSH, to try to increase sperm production.
“Since men can modify the type of underwear they choose to wear, these results may be useful to improve men’s testicular function.”
