Objective: To investigate whether hormonal contraceptive use, its subtypes, and duration of use were associated with new-onset asthma in reproductive-age women.
Methods: Using the Optimum Patient Care Research Database, a UK national primary care database, we constructed an open cohort of 16-45-year-old women (N=564,896) followed for up to 17 years (i.e. 1/1/2000–31/12/2016). We fitted multilevel Cox regression models to analyze the data.
Results: At baseline, 26% of women were using any hormonal contraceptives. During follow-up (3,597,146-person-years), 25,288 women developed asthma, an incidence rate of 7.0 (95%CI 6.9-7.1) per-1,000-person-years. Compared to non-use, previous use of any hormonal contraceptives (hazard ratio [HR] 0.70; 95%CI 0.68-0.72), combined (HR 0.70; 95%CI 0.68-0.72), and progestogen-only therapy (HR 0.70; 95%CI 0.67-0.74) were associated with reduced risk of new-onset asthma. For current use, the estimates were: any (HR 0.63; 95%CI 0.61-0.65), combined (HR 0.65; 95%CI 0.62-0.67), and progestogen-only therapy (HR 0.59; 95%CI 0.56-0.62). Longer duration of use (1-2 years: HR 0.83; 95%CI 0.81-0.86; 3-4 years: HR 0.64; 95%CI 0.61-0.67; 5+ years: HR 0.46; 95%CI 0.44-0.49) was associated with lower risk of asthma onset than non-use.
Conclusion: Hormonal contraceptive use was associated with reduced risk of new-onset asthma in women of reproductive age. Mechanistic investigations to uncover the biological processes for these observations are required. Clinical trials investigating the safety and effectiveness of hormonal contraceptives for primary prevention of asthma will be helpful to confirm these results.
Clinical Implication: Although there are so far no randomized clinical trial directly testing the hypothesis, the current study shows that hormonal contraceptives may serve as a primary prevention strategy for asthma in reproductive-age women.