In recent decades, prompted by concerns that men’s sperm quality is declining, researchers have looked at things they suspect of potentially disrupting the body’s endocrine system — from chemicals in water bottles to Wi-Fi laptops to wearing tight underwear instead of boxers.

You can add ibuprofen to the list.

In a study published last week in the Proceedings of the National Academy of Sciences, researchers found that a concentrated dose of the over-the-counter painkiller taken by young, healthy men appears to be linked to a testicular condition that typically appears only at middle age and has been linked to infertility.

The experiment involved 31 men under 35 in Denmark and France who were split into two groups, with the first taking 1,200 milligrams of ibuprofen each day for six weeks and the other a placebo.

While 1,200 milligrams of ibuprofen is considered on the high side for general aches, pains and fever, it’s not unusual for doctors to prescribe twice that much for athletes.

In two weeks, the concentration of testosterone hormone dropped as ibuprofen concentrations grew in the blood of those taking it — resulting in the men having a condition known as hypogonadism.

Bernard Jegou, a co-author at French National Institutes of Health and Medical Research, and co-authors wrote that ibuprofen appears to “affect the hormonal balance in adult men” and “alters human testicular physiology” — creating a situation where the body has to work harder to maintain some degree of normal testosterone.

Studies about environmental factors that may impact male fertility have become more urgent with evidence that sperm quality is falling globally. While this worry has been around for a long time, there was a lot of skepticism about it until recently.

In July 2017, in a large analysis published by the American Society of Andrology, researchers looking at data from 42,000 men from 1973 to 2011 confirmed that there appears to have been a 52.4 percent drop in sperm concentration in those 40 years.

The current study focuses on a different measure of the male reproduction system — testosterone production rather than semen analysis.

Michael Eisenberg, director of male reproductive medicine and surgery at Stanford and who was not involved with the new study, said the work is important and points to a need for additional research on the topic.

“I do not think the message should be to stop taking ibuprofen. Rather this is an important but small study. Larger studies with more followup are needed to understand the implications of ibuprofen use,” he said.