The findings are dependent on body mass index (BMI), with the prevalence of asthma increasing with BMI, lead investigator Dr. Ferenc Macsali of Haukeland University Hospital in Bergen, Norway, and colleagues report.
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 nonusers of OCs and 961 OC users, or 17% of the study group.
The results were adjusted for smoking, irregular menstruation, BMI, age, type of dwelling, and medical center.
Oral contraceptive use was associated with an odds ratio (OR) for asthma of 1.42. The OR for asthma with hay fever was 1.48; for wheeze with shortness of breath, 1.27; for hay fever, 1.25; and for three or more asthma symptoms, 1.29. The findings were consistent between centers.
The associations were present only among normal weight women (BMI 20-25 kg/m2), who had an OR for asthma of 1.45, and overweight women (BMI >25 kg/m2), who had an OR for asthma of 1.91. Lean women (BMI <20 kg/m2) had an OR of 0.41 for asthma with OC use.
The interaction between BMI and OC use and asthma was statistically significant.
“Women using oral contraceptive pills had more asthma,” Dr. Macsali and associates write in the February issue of the Journal of Allergy and Clinical Immunology. “This was found only in normal weight and overweight women, indicating interplay between sex hormones and metabolic status in effect on the airways.”
The investigators did not gather data on type of oral contraceptives being used.
The findings should be interpreted with caution, Dr. Macsali’s team notes. 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 advise, because even if their study’s findings are eventually confirmed, “the individual health risks related to unwanted pregnancies are much larger than a slightly elevated asthma risk.”
J Allergy Clin Immunol 2009;123:391-397.