Postmenopausal women taking estrogen are more than twice as likely to develop asthma than their counterparts not taking the hormone, according to a new study from Harvard researchers.
The study, published in the Archives of Internal Medicine, examined more than 70,000 women after they had gone through menopause. They found that those taking estrogen were 2.29 times more likely to develop asthma than those who were not taking the hormone. Results were similar for women taking two hormones, estrogen and progestin, as for women taking estrogen alone.
While the results may serve as a cautionary note for older women, R. Graham Barr, lecturer on medicine at Harvard Medical School and assistant professor of medicine and epidemiology at Columbia University, said the main goal of the study was to highlight the connection between asthma and sex hormones such as estrogen.
Barr conducted the study with colleagues from the Channing Laboratory at Brigham and Women’s Hospital, Harvard Medical School, and the Harvard School of Public Health.
Barr said the patterns of development of asthma in the general population have indicated some sort of hormonal role. Asthma is common in young boys before puberty. After puberty, it is more common in girls and that pattern persists into later life.
Despite those apparent patterns, Barr said the scientific literature about the link between female hormones and asthma is contradictory, mainly because of the difficulty of conducting studies that take into account the normal monthly fluctuations in a premenopausal woman’s hormone levels.
By examining postmenopausal women, Barr was able to examine a population experiencing a decline in estrogen levels and compare them with peers who, due to hormone therapy, have higher levels of the hormone.
“In a way, this is a cleaner time in women’s lives [to examine scientifically],” Barr said.
Barr and colleagues examined results of the Nurses’ Health Study, a long-running health survey of 121,700 registered nurses, aged 30 to 55, begun in 1976. Participants were mailed questionnaires every two years, which included questions about medical history, diet, lifestyle, exercise and hormone use. From 1988 to 1996, follow up questionnaires were sent asking about asthma and chronic obstructive pulmonary diseases.
The researchers examined women who had a reported diagnosis of asthma or chronic obstructive pulmonary disease (COPD). The two diseases are on the rise in the United States, with between 5 percent and 8 percent of the U.S. population afflicted with asthma. Chronic obstructive pulmonary disease, which includes chronic bronchitis and emphysema, is the fourth leading cause of death in the United States.
While the link to sex hormones is weaker in COPD, Barr and colleagues examined it along with asthma because its incidence has been rising among women. COPD has traditionally been higher among men, largely due to the higher rates of smoking. Its incidence has been rising among women recently, however, and the number of deaths due to COPD among women passed that among men in 2000.
Despite that trend, however, researchers found no connection between women taking estrogen and incidence of COPD. They found similar results for women taking two hormones, estrogen and progestin, as for women taking estrogen alone.
The results, Barr said, confirm the results of an earlier smaller study, and give a strong correlation between asthma and female hormones. The next step, Barr said, is to examine the association in randomized studies and perhaps to begin to look at the links between hormones and asthma experimentally.
“I think this is very helpful,” Barr said. “This is a large cohort and the study found a strong signal.”