Taking the pill may cut the risk of severe bouts of asthma in women of reproductive age, finds a large long-term study published online in Thorax.
A team of researchers in Sweden and the UK investigated the association between use of hormonal contraceptives and risk of severe asthma exacerbation in reproductive-age women with asthma.
They used the population-based, longitudinal, anonymised Optimum Patient Care Research Database to construct a 17-year retrospective cohort of reproductive-age (16-45 years) women with asthma (n=83,084). The 17-year follow-up resulted in 456,803 person-years of follow-up time.
At baseline, just over a third (34%) of women were using any hormonal contraceptives, 25 per cent combined oestrogen/progestogen contraceptives and 9 per cent progestogen-only contraceptives.
The proportion of women who had bouts of severe asthma rose with increasing age and BMI and a higher number of previous pregnancies. It was also higher in ex- and current smokers than in non-smokers and among women who had had a gynaecological condition.
After taking account of these potentially influential factors, previous and current use of any and combined hormonal contraceptives was associated with a lower, albeit relatively small, risk of severe asthma bouts compared with no use at all.
Previous (incidence rate ratio [IRR], 0.94; 95% CI, 0.92-0.97) and current (IRR, 0.96; 95% CI, 0.94-0.98) use of any contraceptive and previous (IRR, 0.92, 95% CI, 0.87-0.97) and current use of combined (IRR, 0.93; 95% CI, 0.91-0.96) contraceptive were associated with a reduced risk of severe asthma exacerbation compared with non-use, as did longer duration of use (three to four years: IRR, 0.94; 95% CI, 0.92-0.97; five plus years: IRR, 0.91; 95% CI, 0.89-0.93). Progesterone-only contraceptives showed no association with reduced risk of severe exacerbation.
This is the largest longitudinal study investigating the effect of hormonal contraceptives on a key clinical outcome of asthma in reproductive-age women with already established asthma. However, it must be noted that this is an observational study and cannot establish a causative association.
