Compared with looser undergarments, for instance, tighter options were linked to 18 percent higher odds of producing less semen.

Tight undies were also linked to 12 percent higher odds of having fewer motile sperm, 48 percent higher odds of having fewer normally shaped sperm, and 108 percent higher odds of having more sperm with DNA fragmentation or damage.

In a secondary analysis, researchers also found that erectile dysfunction and premature ejaculation were more prevalent in the tight underwear group.

"In conclusion, tight underwear was associated with poorer semen quality and a higher prevalence of erectile dysfunction and premature ejaculation," the authors write, led by urologist Xue-Chun Hu from the University of Science and Technology of China (USTC).