A new study indicates that women who use hormone replacement therapy (HRT) that contains only oestrogen are at 50 per cent higher risk of developing asthma post-menopause compared to those who do not.
The results of the study show that women who have a history of allergies are at even greater risk but the researchers say the total number of women developing asthma post-menopause is very small. The findings also showed the more common combined oestrogen and progesterone form of HRT had no effect on asthma risk.
The study was carried out by Dr Isabelle Romieu from the National Institute of Public Health, Mexico, in partnership with colleagues from the University of South Paris, France, and published in the journal Thorax.
Previous research has revealed an association between asthma and the levels of reproductive hormones (e.g. oestrogen) that show natural variations throughout a womans life. The researchers on this latest study say that the fact the prevalence of asthma in most developed countries is steadily increasing suggests environmental factors may be involved.
It is now well established that certain man-made chemicals can interfere with and even mimic the function of hormones, including oesterogen; these chemicals are collectively known as 'endocrine disrupting chemicals' (EDCs) and include organochlorine pesticides, polychlorinated biphenyls (PCBs), and bisphenol-A (BPA). Many EDCs are now banned but still persist in the environment, and hence in food and water supplies. BPA is used in various plastic products with its use also increasingly being banned. This current research did not look for possible environmental factors however but focused on HRT use.
The study involved 57,664 women who were free from asthma at the onset of menopause. Between 1990 and 2002 postmenopausal French women were asked to complete a questionnaire twice every year. The questionnaire asked the women whether they had ever had an asthma attack before reaching menopause and whether they had a confirmed diagnosis from a doctor during the study period.
Information on the womens lifetime use of hormone therapies, including the contraceptive pill and HRT, was first recorded in the 1992 questionnaire. Data on the brand used, the duration of use and the age the women were when they began taking it was ascertained, as was the type of HRT, i.e. whether it was oestrogen and progesterone (combination HRT) or oestrogen alone.
It is important to factor in other things that vary and could influence the results when conducting scientific research ( these are known as confounding factors) so the researchers also recorded the women's age, calorie intake, body mass index (BMI), smoking habits, contraceptive use, previous pregnancy, and history of allergies. Since the women may not have used HRT throughout the 10 year study period they also accounted for this in their analysis of the results.
The researchers main findings were that recent users (less than 2 years) of HRT of any type had a 25 per cent increased risk of developing asthma while those on oestrogen only therapy had close to a 50 per cent increase compared to women who had never used HRT. The highest risk group was those women who had a history or allergies and also used oestrogen-only HRT. There appeared to be no increase in risk to women using combined HRT in general but those with a history of allergies did have a slightly elevated risk compared women with a history of allergies who had never used HRT.
The researchers say that more work needs to be done to uncover the mechanisms that would explain the interaction between oestrogen levels and the inflammatory processes that lead to asthma.