Being more active could reduce the risk of women developing breast cancer before the menopause, a study has suggested. 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% most active were 10% less likely to develop breast cancer before menopause compared with the least active women. According to NHS England, about one in seven women will be diagnosed with breast cancer in their lifetime, most of whom will be over 50.

Dr Simon Vincent, director of research, support and influencing at Breast Cancer Now, which funded the study, said: "Although breast cancer is more common in older women, 5,000 women aged 45 or younger are given the devastating news that they have breast cancer each year in the UK. 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.

Dr Michael Jones, senior staff scientist at The Institute of Cancer Research, added: "This new research provides us with solid evidence that greater leisure-time physical activity is associated with lower risk of breast cancer in younger women. It's important to remember that breast cancer risk is influenced by several factors, including genetics, lifestyle and environment, and many of these are out of our control.

"Our research adds to the evidence that engagement in higher levels of leisure-time physical activity may lead to reduced premenopausal breast cancer risk. We still need to better understand the biology behind the link between physical activity and reduced breast cancer risk, but these findings add to the strong body of evidence showing that being physically active is good for our health."

Previous studies suggest exercise can lower sex hormones like oestrogen and testosterone, which have been linked to breast cancer risk.