Women are more likely to have asthma. But certain treatments could affect fertility.

Fluctuations in female sex hormones could play a role in the development of allergies and asthma, a major review of evidence suggests.

An analysis of studies involving more than 500,000 women highlights a link between asthma symptoms and key life changes such as puberty and menopause. Many women report that their asthma symptoms change with their menstrual cycle, which may occur due to variations in levels of hormones, including oestrogen and progesterone. Further investigation could help explain why asthma is more common in boys than girls in childhood, but more common in teenage girls and women following puberty.

India is home to one-tenth of the world’s asthmatics. While a gender breakdown is unclear, roughly 7% of Indian children have asthma, as do anywhere from 2 to 12% of adults.

Experts say, however, that the relationship is inconclusive and call for more research.

Researchers at the University of Edinburgh reviewed more than 50 studies of women with asthma from puberty to 75 years of age. They found that starting periods before turning 11 years old, as well as irregular periods, was associated with a higher rate of asthma. Starting menopause — when periods stop and oestrogen and progesterone levels fluctuate — was also associated with a higher chance of having asthma compared with pre-menopause.

“In carrying out this systematic review, we noted that there were many differences between studies investigating hormonal treatments in terms of the type and dose of hormone, and the way patients took the treatment,” said Dr Nicola McCleary, who led the study published in the Journal of Allergy and Clinical Immunology. “This made it difficult to draw firm conclusions from the results. We are now undertaking a project to clarify the role of contraceptives and HRT in asthma and allergy symptoms.”

Another, recent study suggests a link between women and asthma in a different way, finding certain types of asthma medication are linked to difficulty becoming pregnant.

An analysis of more than 5600 women in Australia, New Zealand, the United Kingdom and Ireland revealed women with asthma who used long-acting asthma preventers conceived as quickly as women without the ailment — but women with asthma who used short-acting relievers took 20% longer to conceive on average. They were also 30% more likely to have taken more than a year to conceive, which the researchers defined as the threshold for infertility. The difference remained even after researchers took other factors known to influence fertility, such as age and weight, into account.

“Several studies have identified a link between asthma and female infertility, but the impact of asthma treatments on fertility has been unclear,” says Dr Luke Grzeskowiak, who led the study published in the European Respiratory Journal. “What we don’t yet know is exactly how asthma or asthma treatments lead to fertility problems. As well as affecting the lungs, asthma could cause inflammation elsewhere in the body, including the uterus. It could also affect the health of eggs in the ovaries. Inhaled corticosteroids suppress the immune system, whereas short-acting asthma treatments do not alter immune function. In women who are only using relievers it’s possible that, while their asthma symptoms may improve, inflammation may still be present in the lungs and other organs in the body.”

If more research validates the link, Grzekowiak says the knowledge could lead to less need for fertility treatments, as women with asthma of child-bearing age are directed to treatments that don’t affect their fertility.