A French study of 57,664 women has found that 1.64 per 1000 women per year who used oestrogen-only hormone replacement therapy (HRT) developed new onset asthma, compared to 1.05 per 1000 women per year in those who had never used any form of HRT. This means that the absolute risk of developing asthma increased by less than 1/1000 per year.

Women who used oestrogen-only therapy and had never smoked and those who had some form of prior allergy had the greatest increased risk of developing asthma. 

Oestrogen only therapy is used predominantly by women who have had a hysterectomy. The risk of asthma was not significantly increased in those women using combined oestrogen and progesterone HRT.

Previous studies have linked the development and severity of asthma to female hormones. Asthma can be affected by menstrual cycle and pregnancy and the incidence tends to reduce after menopause (except in those who are overweight).

The researchers warned that although these results indicated an increased risk of asthma associated with oestrogen-only HRT, this risk should be weighed up against the potential improvement in quality of life for women experiencing severe menopausal symptoms.

Jean Hailes Foundation Director Prof Henry Burger noted "The study from which this data was obtained is a large observational study of French female teachers who have been followed long-term for outcomes possibly related to the use of various forms of post-menopausal hormone replacement therapy.  The results for asthma confirm those from the large American Nurses' Health study and from several other publications, except for the finding of a lack of effect for combined hormone therapy. The development of new onset asthma is in the rare category for adverse effects of HRT and would not be considered clinically significant."

Content Updated February 10, 2010