There is also the popular belief that the kind of underwear that men wear can have an impact. Now, new research examines the effect of different types of underwear on the quality of men's sperm.
The lead author of the research is Dr. Lidia Mínguez-Alarcón, who is also a research scientist at the Harvard T.H. Chan School of Public Health in Boston, MA.
Dr. Mínguez-Alarcón and colleagues examined 656 men aged 18–56 who did not have a history of vasectomies and were looking to be treated for infertility at the Massachusetts General Hospital in Boston.
The researchers publish their findings in the journal Human Reproduction.
Boxers may improve sperm quality
The men provided the researchers with semen and blood samples and answered a questionnaire on the type of underwear that they were in the habit of wearing.
The questionnaire included boxer shorts, briefs, bikinis, so-called jockeys, and other forms of tight underwear.
Overall, more than 50 percent of the men said they usually wore boxers. These men had a 25 percent "higher sperm concentration," a 17 percent higher total sperm count, and 33 percent more swimming sperm than men who said they didn't usually wear boxers.
Additionally, men who reported frequently wearing boxer shorts had 14 percent lower serum levels of follicle-stimulating hormone (FSH).
As the study authors explain, FSH drives the production of sperm, and they believe that the higher concentration of FSH in people who do not wear boxers suggests that the hormone gets activated and tries to make up for the testicular damage that other types of underwear might induce.
Importantly, the greatest statistical difference in sperm quality was found between men who wore boxer shorts and men who wore jockeys or briefs.
Choosing boxers may improve fertility
Dr. Mínguez-Alarcón explains what sets this study apart from other research, saying, "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," she continues, "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."
Gonadotropin, the researcher explains, is "a hormone that acts on the testes and that is reflected by the increased levels of FSH." This shows that the body is trying "to increase sperm production."
However, "This hypothesis requires confirmation by further research," cautions the investigator. Also, as the authors mention, the results cannot be generalized to all men because the study participants were already seeking treatment for infertility.
Finally, the study did not confirm causality between tight underwear and FSH levels, merely finding a correlation. Even so, the study points to underwear as a potential modifiable risk factor for infertility.
"Since men can modify the type of underwear they choose to wear, these results may be useful to improve men's testicular function."
Dr. Lidia Mínguez-Alarcón