A small dose of aspirin on alternate days can cut the risk of developing asthma among women, suggests a large study, published ahead of print in Thorax.
The findings are based on almost 40,000 female healthcare professionals, who were part of the Women's Health Study. The women were all aged 45 and above, and had no serious illness, allergy, or asthma at the start of the study.
Participants were either randomly assigned to take 100 mg of aspirin every other day, or a dummy tablet (placebo). And their health was then monitored for around 10 years.
During this time, there were 10% fewer new cases of asthma diagnosed among the women taking aspirin.
In this group 872 new cases were diagnosed compared with 963 among those taking the placebo.
The effect was evident, irrespective of age, menopausal status, exercise levels, and smoking, all factors that might be expected to influence the findings.
And vitamin E supplementation, which was also being tested among the women, to see if it prevented cardiovascular disease and cancer, did not affect the results either.
But aspirin did not lessen the risk of asthma in women who were classified as obese.
Previous research in male doctors showed that aspirin cut the risks of asthma by 22%, although the dose was much higher, at 325 mg every other day.
Among people who have already been diagnosed with asthma, aspirin can worsen symptoms in around one in 10, say the authors. But exactly how low dose aspirin might reduce susceptibility to asthma in adults is not clear.