Aspirin is known to prevent heart attacks but now researchers think it may also help adults ward off developing asthma.

In a large, placebo-controlled study of 22,071 healthy males, researchers found that taking a low dose of aspirin every other day lowered the risk of receiving an asthma diagnosis by 22 per cent.

Researchers at the Division of Aging at Brigham and Women's Hospital in Massachusetts studied male doctors aged 40 to 84 over a period of almost five years. Among the 11,037 individuals who took aspirin, 113 new cases of asthma were diagnosed, as contrasted to 145 in the placebo group.

"We looked at a population that was tolerant for aspirin, meaning they could tolerate it well with no side effects and did not have asthma. Among those, 22 per cent reported less adult onset asthma," Dr. Tobias Kurth, the lead researcher, told Canada AM.

But Kurth notes that the results do not imply that aspirin improves asthma symptoms in those who already have the condition. In fact, he says in a small number of patients, aspirin can actually make it worse, causing severe bronchospasm.

He also warns that the findings are still preliminary.

"I think it's too early to recommend aspirin for treatment to prevent late onset asthma at this point," he said.

"I think it's very important for other research groups at this point to see this link and I hope to motivate other groups to further look at this question."

Asthma is a chronic disease that causes obstructive lung problems. Breathing difficulties from asthma usually occur during attacks, which involve narrowing of the airways, swelling of the lining, tightening of respiratory muscles and an increased secretion of mucus.

Most asthma cases are diagnosed during childhood, a time when the use of aspirin should be avoided because it can make children susceptible to Reye's syndrome, a rare but potentially fatal illness.

Kurth says about five to 10 per cent of the adult population faces the risk of developing adult-onset asthma.

The findings, based on data from the double-blind Physicians' Health Study, appear in the second issue for January 2007 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

The Physicians Health Study began in 1982 to study the effect of aspirin not on asthma but on preventing heart attacks. The study was terminated after 4.9 years when results showed a 44-per-cent reduction in the risk of a first heart attack among those randomly assigned to aspirin.