NEW YORK (Reuters Health) - Some women who use oral contraceptives may have an increased risk for asthma, according to results of a Scandinavian study.

The effect depends on body mass index (BMI), with the rate of asthma increasing as BMI goes up, Dr. Ferenc Macsali of Haukeland University Hospital in Bergen, Norway, and colleagues report in the Journal of Allergy and Clinical Immunology.

From 1999 to 2001, the researchers mailed questionnaires to women ranging in age from 25-44 years in Denmark, Estonia, Iceland, Norway, and Sweden. Respondents included 4,728 women who did not use oral contraceptives and 961 who did.

After taking account of other factors that can influence the risk of asthma, the researchers found that women who took oral contraceptives were 42 percent more likely to have asthma.

When classified by BMI, however, the odds for asthma with oral contraceptive use were 45 higher for normal weight women and 91 percent higher for overweight women, but 69 percent lower for lean women.

The investigators did not gather data on the type of oral contraceptives being used.

The findings should be interpreted with caution, Macsali's team notes, and they advise that women not stop taking oral contraceptives.

"Women who believe they have asthma related to using the pill should discuss anti-asthmatic treatment with their doctors, and alternatively other forms of contraception," the researchers point out.

Even if their study's findings are eventually confirmed, they point out, "the individual health risks related to unwanted pregnancies are much larger than a slightly elevated asthma risk."

SOURCE: Journal of Allergy and Clinical Immunology, February, 2009.

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