Hormone replacement therapy and the risk of asthma attacks: population-based cohort study

Background Women experience higher rates and greater severity of asthma after puberty, suggesting that sex hormones play a key role in airway disease. Hormone replacement therapy (HRT), which acutely alters circulating sex hormone levels, provides a useful model to examine their effects on asthma attacks. We sought to examine the association between HRT use and asthma attacks. Methods We obtained a cohort of women with asthma, aged 45 to 60 years, using nationwide U.K. primary care health records linked to hospital and mortality data, 2004–2 020, to compare HRT-users to non-users. We applied inverse-probability of treatment weighting and Cox proportional hazards, accounting for demographics, asthma severity and comorbidities; stratifying by potential modifiers: body mass index (BMI), blood eosinophil count, smoking and HRT-type (oestrogen-only, progesterone-only and combined). Results 182 010 women were eligible for the study, of whom 9663 were incident HRT users and 172 347 were non-users. Median age was 52 years (IQR: 50–55 years). HRT-users and non-users were broadly similar in terms of BMI, smoking history but non-users had slightly higher proportions residing in more deprived areas, with more comorbidities, higher reliever use and asthma attacks in the year before study entry, but lower use of preventer inhalers. After applying weighting, there was no association found between HRT use and asthma attacks (weighted-HR 0.97, 95% CI 0.90–1.04). There was no modification of that association by blood eosinophil level, BMI, smoking history or HRT-type. Conclusion Hormone replacement therapy use is not associated with asthma attacks in women with established asthma aged 45 to 60 years old.