Heart and lungs

HRT linked to asthma risk

“Women taking oestrogen-only HRT may have a higher risk of developing asthma”, reported the Daily Mail . It said a study of almost 58,000 women who were free of asthma before the menopause suggested there could be a 50% increased risk.

Although the study found a difference in the risk of asthma for women who had taken oestrogen-only HRT, the actual number of women who developed asthma was relatively low, and developing asthma after menopause is generally quite rare. Combined hormone therapies that included progesterone, the main type of HRT in use, did not have an effect on asthma risk.

The mechanisms by which oestrogen may affect asthma were not assessed in this study. Further research will be needed to establish why these different hormones have these effects on the inflammation that underlies asthma.

It is important to note that you should speak to a doctor if you experience regular symptoms such as breathlessness, cough or wheeze.  

Where did the story come from?

This research was carried out by Dr Isabelle Romieu from the National Institute of Public Health, Mexico and colleagues from the University of South Paris, France. The study was funded by Mutuelle Générale de l’Education Nationale, the Institut de Cancérologie Gustave Roussy and the Institut National de la Santé et de la Recherche Médicale. The paper was published in the peer-reviewed medical journal Thorax.

The research was covered accurately by the press.

What kind of research was this?

This prospective cohort study investigated whether the onset of asthma in post-menopausal women is affected by HRT. It looked at different types of therapy and how long they were used.

The researchers say that the increase in the prevalence of asthma in most developed countries suggests environmental factors may be involved. Previous studies have shown there to be an association between asthma and the levels of reproductive hormones (such as oestrogen) that fluctuate naturally throughout a woman’s life.

What did the research involve?

The research was carried out between 1990 and 2002. During this time, postmenopausal French women were asked to complete a questionnaire twice a year. The study analysed the data from 57,664 women who were free from asthma at the onset of menopause.

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.

Information on the women’s lifetime use of hormone treatments, including the contraceptive pill and HRT, was first recorded in the 1992 questionnaire. This asked about the brand used, the duration of use and the age the women were when they began taking it. The type of HRT, such as whether it was oestrogen and progesterone (combination HRT), or oestrogen alone, was also recorded. Women were categorised as ‘never users’ or ‘ever users’ of HRT, with 'ever users' being women who had used HRT at any point after menopause.

The participants’ body mass index (BMI), smoking history and allergies were also recorded. As some of the women may not have been on HRT for the whole length of the study, the researchers used ‘person-years’ to calculate the risk of developing asthma. This takes into account the number of years each individual was on HRT.

What were the basic results?

There were 569 new cases of asthma over the 10-year study period, corresponding to 1.15 women out of every 1000 each year.

At the start of the study, the women who had ‘ever used’ HRT were more likely to have a lower BMI and previously used oral contraceptives.

Women who had ‘ever used’ HRT had a slightly higher but non-significant risk of developing asthma compared to ‘never users’. This was after adjusting for age, smoking, BMI, contraceptive use, previous pregnancy and calorific intake. Recent HRT users (women using HRT for less than two years) had a small, significant increase in risk compared with 'never users' (Hazard ratio [HR] 1.25 95% confidence interval [CI] 1.02 to 1.53).

When looking at the type of HRT, women who had taken oestrogen alone had a higher risk of asthma onset than ‘never users’ (HR 1.54, 95% CI 1.13 to 2.09). There was no increased risk for women who took combination HRT.

Oestrogen only had an effect on increased risk of asthma onset for recent users and not past users (women who had stopped taking treatment one-and-a-half years before) (HR 1.04, 95% CI 0.51 to 2.12).

Among ‘never smokers’, HRT use was related to the risk of asthma onset. However, for smokers, the HRT-associated risk was not present (HR 1.45, 95% CI 1.10 to 1.90 [non-smokers] and 1.02, 95% CI 0.79 to 1.31 [smokers]).

Women who reported a history of allergies and who received oestrogen-only HRT appeared to have a higher risk of asthma related to HRT than those receiving this type of HRT but who did not have a history of allergies (HR 1.86, 95% CI 1.18 to 2.93). There was a marginally significant increase in risk for asthma in the allergy group compared with women with no prior history of allergies who were taking combination HRT (HR 1.39, 95% CI 1.01 to 1.91).

How did the researchers interpret the results?

The researchers concluded that: “the use of oestrogen alone was significantly associated with an increased risk of asthma onset in postmenopausal women, after adjustment for potential confounding factors. The increase in risk was mostly observed among women reporting an allergic disease prior to asthma onset and in ‘never smokers’. In these subgroups, the risk of asthma onset was strongly related to the use of oestrogen alone and a marginal association was observed with the use of oestrogen/progestogens”.

They say that there is still uncertainty as to the mechanism by which female hormones affect asthma risk.


This large cohort study found an association between oestrogen-only HRT and an increased risk of asthma in postmenopausal women. The researchers mention some limitations:

  • They suggest that it is possible some women might not have asthma but other respiratory diseases such as bronchitis or emphysema. This potential limitation of the study has occurred because the researchers relied on the participants reporting their diagnosis from the doctor, and did not themselves measure the participants’ lung function.
  • They also suggest that women taking HRT may be more likely to frequently visit the doctor. As such, asthma attacks could be diagnosed more often than in women who paid less frequent visits to the doctor.

Oestrogen-only HRT is usually given to women who have had a hysterectomy and do not require progesterone to maintain the functions of the womb. The study did not find an increased risk of asthma with combined HRT treatments, suggesting that the hormones work in different ways.

Although the study found a difference in the risk of asthma for women who had taken oestrogen only HRT, the actual number of women who developed asthma was relatively low, and developing asthma after menopause is generally quite rare. However, it is important to speak to a doctor if you start to experience regular symptoms such as breath-lessness, cough or wheeze. The mechanisms by which oestrogen may affect asthma were not assessed in this study. Further research into how oestrogen affects asthma is warranted.

NHS Attribution