According to the article, because the incidence of asthma changes depending on a person's age, researchers suspect that reproductive hormone therapy may influence the development of the disease, which affects 5 percent to 8 percent of the United States population. Studies also suggest that incidence of COPD, the fourth leading cause of death in the United States, also may be influenced by sex hormones.

R. Graham Barr, M.D., Dr.P.H., of Brigham & Women's Hospital, Boston, and colleagues evaluated whether postmenopausal women using hormone therapy were at an increased risk for newly diagnosed asthma or COPD. Dr. Barr is now at Columbia Presbyterian Medical Center, New York.

The researchers used data from the Nurse's Health Study, which enrolled 121,700 married female registered nurses, aged 30 to 55 years old in 1976. Participants were mailed questionnaires biennially (once every two years) which included questions about medical history, diet and lifestyle, exercise, and hormone use. From 1988 to 1996, biennial follow-up questionnaires were sent inquiring about new asthma and COPD diagnoses.

The researchers found that current use of estrogen alone was associated with increased risk (2.29 times higher) of asthma compared with women who never used hormones. Women who used estrogen plus progestin had a similar increased rate of newly diagnosed asthma. However, the rates of newly diagnosed COPD among hormone users and non-hormone users were similar.

"Postmenopausal hormone use was associated with an increased rate of newly diagnosed asthma but not newly diagnosed COPD," the authors write. "Female reproductive hormones may contribute to the onset of asthma among adult women, but do not appear to hasten the development of COPD."