Estrogen-only hormone therapy has been shown to increase the risk of developing asthma after menopause by 54% among postmenopausal women compared with those never treated with HT, according to a new analysis.
Researchers at the National Instituto of Public Health, Cuernavaca, Mexico, and INSERM and the Université Paris-Sud, France, used data from the E3N cohort, a health survey of nearly 100,000 French women born between 1925 and 1950. The women, mostly teachers, responded to biannual questionnaires between 1990 and 2002 (Thorax 2010 Feb. 8 [doi:10.1136/thx.2009.116079]).
Of the 57,664 women free of asthma at menopause, just under two-thirds used some sort of HT, and 569 were later diagnosed with asthma. The study, led by Dr. Isabelle Romieu of the Mexican institute, found that “the increased risk of asthma onset among women using [HT] was present only in users of estrogen alone [hazard ratio 1.54]. The effect was observed only in recent users including current users and women for whom time since last use was <1.5 years.”
Moreover, the authors wrote, “Fifty-eight percent of women reporting the use of estrogen alone at the time of asthma onset or as last treatment before asthma onset had previously used another [HT]. This supports our finding that the increased risk of asthma onset is linked to estrogen use.”
The authors found the risk of developing asthma increased to 80% and 86% (hazard ratios of 1.80 and 1.86), respectively, among postmenopausal women treated with estrogen-only HT who never smoked or had a history of allergies before menopause, compared with untreated women. The authors cautioned, however, that the allergy histories were self-reported and that potential misclassifications of allergic disease could have occurred.
The apparently lower susceptibility of HT-treated women who smoke or have smoked to postmenopausal asthma, the authors said, had been noted in earlier studies. “This might be due to the antioestrogenic effect of smoking or to the difficulty of isolating the additional effect of [HT] among smokers,” they wrote.
Female hormones have long been suspected to play a role in the development of asthma, and the connection between HT and postmenopausal asthma had been investigated in a large-scale U.S. study published in 2004 (Arch. Int. Med. 2004;164:379-86). That study determined that recent HT treatment was linked to an increased risk of postmenopausal patients developing asthma. But it found the risk to be similar whether patients were treated with estrogen only, or a combination therapy.
Dr. Romieu and colleagues offered as a possible explanation for the disparity the fact that French and American physicians generally use different ratios of estrogen and progestin, as well as different types of progestin, in HT treatment regimens.
Also in contrast to the earlier U.S. study, Dr. Romieu's team did not observe interactions between body mass index and risk of asthma among HT and non-HT patients following menopause, but stated that this may have been because the French cohort presented leaner body mass as a whole.
Disclosures: The study investigators reported no financial conflicts of interest.