They found women who took a small dose of aspirin -- 100 mg every other day -- were 10 percent less likely to develop asthma over 10 years than women given placebos.
Writing in the journal Thorax, the researchers said their findings reinforce studies that show men who took aspirin daily were less likely to develop asthma, too.
"Although aspirin can worsen symptoms in some patients with asthma, our biologically plausible finding long with similar results from a large randomized trial in men and observational cohort studies in women suggests a small benefit of aspirin for the prevention of the development of asthma in adults," wrote Dr. Tobias Kurth and colleagues of Brigham and Women's Hospital and Harvard Medical School in Boston.
"However, before public recommendations are provided, results from randomized trials are needed that are specifically designed to test whether low-dose aspirin reduces the risk of asthma," they added.
Kurth's team studied 37,000 female healthcare professionals taking part in a study called the Women's Health Study. All were aged 45 and above, and had no serious illness, allergy or asthma at the start of the study.
They were randomly assigned to take 100 mg of aspirin every other day, or a dummy tablet.
Among the women who got real aspirin, 872 developed asthma over the 10 years, compared to 963 taking the placebo.
Women who were obese, with a body mass index of 30 or above, got no benefit from aspirin, they noted.
"The effect of aspirin on adult-onset asthma was not significantly modified by age, smoking status, exercise levels, postmenopausal hormone use or randomized vitamin E assignment," they added.
Aspirin can affect compounds involved in inflammation and the hyper-response of airways that is seen in asthma.
The researchers noted that between 4 percent and 11 percent of patients with asthma have an acute response to aspirin.
Last Mod: 13 Mart 2008, 18:00