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TUESDAY, March 30 (HealthDayNews) -- Frequent use of the popular painkiller acetaminophen may increase your risk for developing asthma, a new study suggests.

Women taking acetaminophen at least 15 days a month for six years had a 63 percent higher incidence of developing asthma, compared with women who never used the analgesic, researchers say.

However, it's far too early to recommend that consumers shy away from using acetaminophen, the researchers add. Individual reactions to various pain relievers vary widely and "we are not trying to say that all asthmatics should stop using acetaminophen," says study author Dr. R. Graham Barr, of Columbia University.

His team's findings appear in the current issue of the American Journal of Respiratory and Critical Care Medicine.

Soaring rates of asthma across the United States have alarmed public health officials and puzzled asthma experts.

"People estimate that between the 1970s and 2000, at least in younger children, asthma cases approximately doubled," says Dr. Susan Redline, an asthma expert at Rainbow Babies and Children's Hospital in Cleveland.

However, the exact cause of this steep climb in asthma rates remains unclear. Rising rates of obesity -- which can impair lung function -- have been cited as a possible culprit, as have indoor pollutants such as dust mites and mold.

But the upswing in new asthma cases also coincided with the increasing popularity of over-the-counter acetaminophen, the study researchers note. An estimated 200 over-the-counter drugs, including cold and headache remedies, contain acetaminophen, according to the American Medical Association. One of the best known is Tylenol.

In their study, Barr and his colleagues examined data from the Nurses Health Study, a decades-long, prospective study of nearly 122,000 adult women. As part of the study, each participant was asked to keep a record of her analgesic use as well as the development of any new medical conditions, including asthma.

Among women who used acetaminophen for more than half of the days in a given month, "there was a significant increase (63 percent) in the risk of a new diagnosis of asthma," Barr says. The design of the study prevented researchers from determining whether acetaminophen was linked to worsening symptoms in women already diagnosed with asthma.

Scientists have long known that acetaminophen lowers blood levels of a natural compound called glutathione. "Glutathione has an antioxidant effect in the body, particularly in the lungs," Barr explains. When glutathione levels plummet, "that may reduce the antioxidant defenses in the body and increase the possibility of developing asthma."

However, the current study only demonstrates an association between acetaminophen and increased asthma -- not a cause-and-effect relationship. And Barr notes that other analgesics such as aspirin, ibuprofen and non-steroidal anti-inflammatory drugs (such as Celebrex and Vioxx) have also been shown to affect asthmatics in various ways.

"For example, it has been well described that some people get asthma from taking aspirin, but then a lot of people with asthma do fine taking aspirin," he says.

Barr's advice: "If individuals happen to notice that their asthma gets worse after they take aspirin or non-steroidals, or acetaminophen, it's worth reassessing that usage. But we're not making any blanket statements."

Redline, an editor at the American Journal of Respiratory and Critical Care Medicine, agrees. "Until we have more information, I think people with uncontrolled asthma should just continue to discuss the issue with their doctors," she says.

More information

For information on asthma and the control of asthma symptoms, visit the Asthma and Allergy Foundation of America or the American Academy of Allergy, Asthma & Immunology.

(SOURCES: R. Graham Barr, M.D., DRPH, associate professor, medicine and epidemiology, Columbia University, New York City; Susan Redline, professor, pediatrics, Rainbow Babies and Children's Hospital, Cleveland; March 26, 2004, American Journal of Respiratory and Critical Care Medicine)

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