Occasional reviews Do exogenous oestrogens and progesterone influence asthma?

Between 20% and 40% of women of childbearing age in the UK use hormonal contraceptives. 2 In a survey carried out in Oxfordshire in 1990 about 20% of women aged 45–64 years were taking hormone replacement therapy (HRT). Around 5% of women of childbearing age in the UK have diagnosed asthma, and a higher proportion have asthmalike symptoms. There is less information available about the prevalence of asthma in older women, but there is little doubt that it is a common problem in this age group also. There are no special guidelines on the prescription of hormonal contraceptives or hormone replacement therapy to women with asthma. Should we be concerned about the eVect of oestrogens and progesterone on the risk of developing asthma? Should women with asthma avoid hormonal contraceptives and HRT? Or could they have a therapeutic role? The prevalence of asthma and asthma-like symptoms is similar in adult men and women but women have a higher risk of hospital admission for asthma than men. While this may be due to diVerences in illness behaviour and thresholds for admission, it may be that women have more severe symptoms, which could be due to their endogenous or exogenous levels of sex hormones. A recent paper documented the rise in asthma prevalence over the last 30 years and noted the parallel increase in the use of the oral contraceptive pill, hypothesising that hormonal contraceptives might increase the risk of asthma in subsequently born children. Could they also influence the risk of asthma in women themselves? A body of research that has attempted to explore the influence of exogenous oestrogen and progesterone on the incidence and severity of asthma is reviewed here. There are theoretical reasons why oestrogens and progesterone might be expected to influence the clinical expression of asthma. Pregnancy is associated with changes in immune function. Animal studies have shown that oestrogens have many eVects on humoral and cellular immunity, influence smooth muscle function, and have eVects on the cholinergic and adrenergic systems. Prostaglandins, which have been implicated in the pathogenesis of asthma, may be partially controlled by the levels of sex hormones. 15 However, it is not clear what these findings mean for women considering taking hormonal contraceptives or oestrogen replacement therapy.