The study, published online by the British Medical Journal ahead of print in Thorax, found there were 10 percent fewer new cases of asthma diagnosed among the women taking aspirin -- irrespective of factors such as age, menopausal status, exercise levels and smoking that might be expected to influence the findings.

The researchers at Brigham and Women's Hospital and Harvard Medical School in Boston found aspirin not lessening the risk of asthma in women classified as obese.

The findings are based on almost 40,000 female healthcare professionals, who were part of the Women's Health Study. The women were all age 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 placebo and their health was then monitored for around 10 years.

Previous research in male doctors showed that aspirin cut the risks of asthma by 22 percent, although the dose was much higher -- 325 mg every other day.