OBJECTIVES: Sex steroid hormones may explain known gender-related variations in asthma prevalence and clinical manifestation. We investigated the relationship between use of hormonal contraceptives and asthma in women, and assessed evidence of biological interaction between use of hormonal contraceptives and body mass index in this relationship.
DESIGN: Population-based analysis using data from serial (i.e. 2003, 2008 and 2010) Scottish Health Surveys.
SETTING: Random samples of the Scottish general population.
PARTICIPANTS: A total of 3257 non-pregnant, 16-45-year-old women.
EXPOSURE: Current use of hormonal contraceptives.
MAIN OUTCOME MEASURES: Self-reported current physician-diagnosed asthma, current wheezing symptoms, wheezing attacks and treatment for asthma or wheeze.
RESULTS: Women comprising 30.9% (95% confidence interval 29.3-32.5) were currently using any hormonal contraceptive and current physician-diagnosed asthma was present in 6.5% (95% confidence interval 5.7-7.4). Use of any hormonal contraceptive was associated with reduced risk of current physician-diagnosed asthma (odds ratio 0.68; 95% confidence interval 0.47-0.98) and receiving ≥3 asthma care episodes (odds ratio 0.45; 95% confidence interval 0.25-0.82), but the evidence was equivocal for wheezing attacks. Use of hormonal contraceptives among overweight or obese women was non-statistically significantly associated with asthma, but there was 42-135% increased risk in overweight and obese non-contraceptive using women.
CONCLUSIONS: Use of hormonal contraceptives may reduce asthma exacerbations and number of care episodes. Overweight and obese non-contraceptive-using women may be at increased risk of asthma. Prospective studies are now needed to confirm these findings. Both oestrogen and progesterone may stimulate smooth airway muscle function and inhibit the activities of TH2 responses. Future studies should investigate these underlying mechanisms.