Even acetaminophen (Tylenol) may put a developing boy's future reproductive health at risk, suggest findings from a study of some 2,300 Danish and Finnish women by Henrik Leffers, MD, PhD, of Rigshospitalet, Copenhagen, Denmark, and colleagues.
The researchers suggest that acetaminophen, ibuprofen, aspirin, and other NSAID painkillers act as hormonal "endocrine disruptors" and interfere with normal male sexual development. Chemicals in the environment, such as phthalates, act as endocrine disruptors and have in the past been blamed for harmful effects on human sexual development.
"A single [acetaminophen] tablet (500 milligrams) contains more endocrine disruptor potency than the combined exposure to the ten most prevalent of the currently known environmental endocrine disruptors during the whole pregnancy," Leffers says in a news release.
Despite the strong language, the researchers note that their findings are based on a small number of boys whose testicles were late to descend -- a risk factor for poor future semen quality. While they note that more study is needed, they stress the urgency of such studies.
"Although we should be cautious about any over-extrapolation or overstatement ... the use of these compounds is, at present, the best suggestion for an exposure that can affect a large proportion of the human population," Leffers says.
The Leffers study is based on questionnaires from the mothers of 834 Danish boys and 1,463 Finnish boys, and on interviews with the mothers of 491 Danish boys (285 of whom also were among those who filled out the questionnaires). All of the boys were examined for signs of undescended testicles (congenital cryptorchidism).
In the end, the researchers identified only 42 boys with signs of undescended testicles. Over 64% of these boys were born to mothers who took painkillers during pregnancy.
Women who took more than one kind of mild painkiller were more than seven times more likely to have a boy with signs of undescended testicles.
It appeared that painkillers taken during the second trimester of pregnancy were particularly risky -- increasing risk of congenital cryptorchidism by 2.3-fold.
Nevertheless, these risks are based on very small numbers of affected boys. The vast majority of boys born to women who reported painkiller use did not have any sign of undescended testicles.
Leffers and colleagues will continue to follow up on the boys through sexual maturity.
Leffers' team also performed rat studies showing that acetaminophen and NSAID painkillers can affect sexual maturation.
The Leffers study appears in the advance online edition of the journal Human Reproduction.