The researchers theorize that FSH levels were higher in men who wore close-fitting underwear because their bodies were trying to compensate for the lower sperm count.

Author, Jorge Chavarro, an associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health explained that beyond providing additional evidence that underwear choices may impact fertility, the 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.

The study was published on Wednesday in the journal Human Reproduction.

“These results point to a relatively easy change that men can make when they and their partners are seeking to become pregnant.”- Lead author Lidia Mínguez-Alarcón