A new study has found exercising for half an hour a day slashes the risk of developing breast cancer by 21 per cent.

Middle aged women who do half an hour of exercise a day cut their chance of developing breast cancer by a fifth, claims new research.

Whether you like to cycle, swim, or dance, the benefits of exercise are enormous. From dropping a few pounds to helping your body fight illness, exercise is the key to a healthy life. And now researchers at Oxford University have found that obese women are over 50 per cent more likely to develop breast cancer than those who are slim. They spent three years following 126,000 women who had been through the menopause, recording whether they developed the disease. Participants were also required to fill in detailed questionnaires on subjects such as how often they exercised, their diet, weight and drinking and smoking habits.

Results showed women who did three hours of vigorous physical activity every week were 21 per cent less likely to develop breast cancer than those who did little or no exercise. Vigorous exercise included intensive gym classes such as spinning and Zumba, but not gentle jogging, walking or cycling.

Other findings suggested that women with the highest body fat were 55 per cent more likely to develop the illness, compared to slimmer participants.

One theory scientists from Oxford have voiced, is that intensive physical activity further lowers the amount of oestrogen produced.

"What's really interesting about this study is that [reduction in breast cancer risk] does not appear to be solely due to the most active women being slimmer, suggesting that there may be some more direct benefits of exercise for women of all sizes," said Professor Tim Key, a Cancer Research UK scientist from the cancer epidemiology unit at Oxford University.

"We don't yet know exactly how physical activity reduces risk... but some small studies suggest that it could be linked to the impact on hormone levels in the body."

Professor Key added more research needs to be done to look at the link between women's hormone levels and the apparent prevention of cancer.

The new findings come hot on the heels of a recent poll which found 75 per cent of women fail to work out because of fear of being judged. Research conducted by Sport England polled 9.4 million women aged 14 to 40 as part of the This Girl Can campaign, and found 7.1 million would like to exercise more. Reasons why they don't, include fear of being judged over their appearance and ability at the gym.

"We found out by talking to women of all ages up and down the country that what's stopping them is fear, fear of judgment: whether that's about how they look, whether they're any good at it, or feeling guilty about spending time on themselves," Jennie Price, chief executive of Sport England.

"Whichever way you slice it, women's fear of judgment is sapping their confidence."