Estrogen linked to adult asthma risk.

Estrogen replacement therapy may increase a woman's chance of developing asthma, say researchers from Harvard Medical School in Boston. They found that women taking postmenopausal hormones were 50 percent more likely to suffer adult-onset asthma than women who had never taken the hormones.

The finding could also help explain why severe adult-onset asthma afflicts more women than men.

"It is not clear how estrogen affects airways," says study collaborator Frank E. Speizer. "But estrogen usage is one more risk factor to be considered in women with asthma."

About 5 percent of the U.S. population suffers from asthma--a reversible but potentially life-threatening breathing disease characterized by coughing and wheezing. The disease displays a distinctive pattern of gender bias. Severe childhood asthma strikes more boys than girls, but in adulthood, asthma's severe forms strike more women than men.

Scientists have some evidence that the reproductive hormone estrogen may play a pivotal role in these gender differences. In women, the number of asthma cases soars at the onset of puberty, when the ovaries begin to produce large amounts of estrogen. The incidence remains relatively high throughout the reproductive years. Moreover, animal studies indicate that estrogen can inhibit airflow through the lungs.

In light of estrogen's tenuous link to asthma, the Harvard team compared asthma incidence to postmenopausal hormone use in 23,035 women participating in the Nurses' Health Study. As the researchers report in the October American Journal of Respiratory and Critical Care Medicine, women who reported using hormone replacement therapy at any time were 50 percent more likely to suffer from asthma than women who had never used postmenopausal hormones. And asthma has twice the normal incidence among women who had used the hormones for 10 or more years.

"This is a significant increase in risk of asthma," says Speizer. "Physicians should consider it as one more risk factor, like a strong family history [of the disease]."

Susan Redline of Case Western Reserve University School of Medicine in Cleveland notes that the Harvard study is the first to look at the association between estrogen and asthma by monitoring a group of initially healthy women and comparing differences between those who subsequently suffer asthma and those who do not.

"I think the implication that hormone replacement therapy may modify [susceptibility to] asthma is a very intriguing observation," says Redline. "And it may offer a clue as to why women suffer more asthma than men."

Both Speizer and Redline maintain that more research into estrogen's effect on lung tissue is needed to firmly establish the link between estrogen and asthma. Until then, Speizer notes, estrogen's proven benefits in maintaining bone and cardiovascular health will outweigh any risk of asthma for most women.