Breast cancer and exercise

A study published in the Journal of the National Cancer Institute found that women who were physically active in their leisure time, especially as teenagers and young adults, were less likely to develop breast cancer before the menopause than women who were inactive.

"Earlier research showed a link between exercise and lower breast cancer risk after the menopause, but the link before the menopause wasn't proven," says Dr Sonia Maruti.

In a study of women in the Nurses' Health Study II, the risk of breast cancer fell as physical activity rose, and the link was strongest for women who were active throughout their lives. Exercise between 12 and 22 contributed most to lowering the risk.

The activity needed to cut the risk by 23% was equal to 3.25 hours of running or 13 hours of walking a week. The breast cancer rate among the most active women was 136 per 100,000 a year, against 194 per 100,000 among the least active young women. The results show that the more active a woman is throughout life, the lower her risk of breast cancer.