Low doses of ASA may help reduce the incidence of asthma in adults, a new study suggests, but are not helpful in treating symptoms.

Men who took a low dose of ASA every other day lowered the risk of being diagnosed with asthma by 22 per cent, researchers report in Monday's American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

Aspirin exacerbates asthma in a minority of people, but can also reduce its incidence.
(Getty Images)

But the findings do not imply that ASA improves symptoms in people with asthma, cautioned lead researcher Dr. Tobias Kurth, from Brigham and Women's Hospital in Massachusetts.

"Indeed, Aspirin can cause severe bronchospasm in some patients who have asthma,” said Kurth. "Because asthma was not the primary endpoint of the U.S. Public Health Service study, additional randomized trials would be helpful to confirm the apparent reduction in asthma incidence caused by Aspirin."

Researchers carried out a randomized, placebo-controlled study of more than 22,000 healthy male physicians.

Among the 11,037 men who took the drug, 113 new cases of asthma were diagnosed, compared with 145 in the placebo group.

The trial was designed to test whether ASA reduced the risk of heart attacks. It was ended early after almost five years when the drug showed a 44 per cent reduced risk of first heart attack among those taking it.

ASA exacerbates asthma in four to 11 per cent of adults, and a much smaller proportion of children, according to previous population-based studies.

Based on the study's findings, 1,000 people would have to be given ASA to prevent about three cases of asthma.

The drug also carries risks of side-effects such as stomach bleeding.