Oestrogen-only hormone replacement therapy (HRT) may increase the risk of developing asthma after the menopause, suggests a large-scale study published ahead of print in the journal Thorax.
The risk of asthma was significant only among those using oestrogen alone. Among these women the overall risk of asthma was 54% higher than among those who had never used any form of HRT.
Oestrogen-only users who had never smoked and those who had had some form of allergy before their asthma diagnosis were at greatest risk of developing asthma – 80% and 86% higher, respectively.
A small increased risk for asthma was also seen in women using combined oestrogen and progesterone HRT who were either non-smokers or who had had some form of allergic reaction in the past.
Previous research has suggested that female hormones may have a role in the development and severity of asthma, say the authors.
The disease is more common in young women after they have started having periods, while hospital admissions for asthma are more common among women than men.
The severity of asthma also varies throughout the menstrual cycle and during pregnancy, and the incidence of the disease tends to fall after the menopause, except among those who put on a lot of weight, the authors point out.
They conclude that while their findings point to an increased risk of asthma, this must be judged in "the light of all the other health effects of HRT use, including its beneficial effect on the quality of life of menopausal women."