The surprising finding comes from a multination European study of 1,274 women age 45 to 56. About a third of the women had reached menopause; none was taking hormone therapy for menopausal symptoms.
Earlier studies have found no link between menopause and asthma or respiratory problems. But those studies did not take women's weight into account, note Francisco Gomez Real, MD, of Norway's Haukeland University Hospital, and colleagues.
The researchers stratified the women according to their body mass index or BMI -- a measure of weight adjusted for height. Those with a BMI of less than 23 had a fourfold higher risk of asthma symptoms. The normal BMI range is 18.5 to 24.9; the overweight range is 25 to 29.9, and a BMI of 30 or more indicates obesity.
Obese women, too, were at somewhat higher risk of asthma symptoms when they entered menopause.
"Women undergoing the menopausal transition might be at risk of deteriorating lung health," Gomez Real and colleagues suggest. "This applies to lean women and, to some extent, to obese women."
Women with a BMI between 23 and 28 appear to have the lowest risk of asthma when they go through menopause.
Why asthma at menopause? That's not clear. Gomez Real and colleagues suggest that declining estrogen levels increase insulin resistance, which in turn increases risk of lung inflammation. As fat tissue produces estrogen, the leanest women would be at the highest risk.
Despite the estrogen production from their extra fat, obesity itself increases insulin resistance. So obesity, the researchers suggest, cancels out the extra protection afforded by extra estrogen production by fat cells.
Gomez Real and colleagues report their findings in an in-press issue of the Journal of Allergy and Clinical Immunology, published online Oct. 29, 2007.