Being more active could reduce the risk of women developing breast cancer before menopause, a study has suggested.
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Researchers analysed data based on the amount of exercise women reported doing during leisure time - such as walking, cycling or sports - finding "solid evidence" of a lower breast cancer risk.
But they added that risk levels were influenced by several factors, including genetics.
The team from The Institute of Cancer Research, London, looked at self-reported leisure-time physical activity from 19 studies, comprising a total of 547,601 premenopausal women.
They were followed up for an average period of 11-and-a-half years, during which 10,231 were diagnosed with breast cancer before going through the menopause.
Ranking the data, researchers found those in among the 10 per cent most active were 10 per cent less likely to develop breast cancer before menopause compared with the least active women.
"Although breast cancer is more common in older women, 5000 women aged 45 or younger are given the devastating news that they have breast cancer each year in the UK," said Dr Simon Vincent, director of research at Breast Cancer Now.
"Breast cancers in younger women tend to be more aggressive and diagnosed at a later stage, so we urgently need to find new ways to prevent people from developing the disease.
"While we can't predict who will get breast cancer, there are some things people can do to lower their risk of getting it.
"This research highlights how vital it is that we support women to start making small, healthy lifestyle changes that can positively impact their health and help lower their risk of breast cancer."
The findings have been published in the Journal of Clinical Oncology.
Previous studies suggest exercise can lower sex hormones like oestrogen and testosterone, which have been linked to breast cancer risk.
Australian Associated Press
