Researchers have found that fluctuations in female sex hormones can play a major role in the development of asthma and allergies. The analysis of studies involving more than 5,00,000 women highlights a link between asthma symptoms and key life changes such as puberty and menopause. "Asthma and allergy symptoms are often affected by life events such as puberty and menopause, but the reasons behind this are unclear," lead author of the study, Nicola McCleary from the University of Edinburgh, said. For the study, published in the Journal of Allergy and Clinical Immunology, researchers 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. The onset of menopause -- when periods stop and oestrogen and progesterone levels fluctuate -- was also associated with a higher chance of having asthma compared with pre-menopause. Many women report that their asthma symptoms change with their menstrual cycle, which may be down to variations in levels of hormones, including oestrogen and progesterone, but the link is unclear, the researcher said. "Our ultimate goal is to undertake a clinical trial to test the effectiveness of hormonal treatments to reduce symptoms of asthma in women," said co-author of the study Aziz Sheikh from the University of Edinburgh.