Researchers from the University of North Carolina Gillings School of Global Public Health (United States) found that women who exercised during their childbearing years were less likely to develop breast cancer after menopause. And even if exercise was only introduced after menopause, the risk was still lower than for inactive counterparts.

For the study, lead researcher Lauren McCullough and colleagues collected data on more than 1 500 women with breast cancer and a similar number of women without the disease.

They found women who exercised before or after menopause had a reduced risk of breast cancer.

Women who exercised 10 to 19 hours a week had the largest benefit – about a 30% reduced risk.

The risk of breast cancer was cut with any amount of exercise. The risk reduction was seen mostly for hormone receptor-positive breast cancer, which is one of the most common types of breast cancer diagnosed.

Conversely, weight gain seemed to raise a woman’€™s chance of breast cancer. Even among active women, gaining a significant amount of weight, particularly after menopause, increased the risk of breast cancer, negating the beneficial effect of exercise, the researchers found.

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But like past studies, the current study only points to a correlation between exercise and a reduction in breast cancer risk, it does not prove that exercise, itself, is what cut women’s breast cancer risk.

The benefit of exercise may lie in its potential of reducing a woman’€™s weight. Excess body fat is related to higher levels of certain hormones, including oestrogen, and growth factors, which can feed tumour development.

A study reported last month in the Journal of Clinical Oncology found that weight loss by overweight women may lower their exposure to biomarkers associated with breast cancer. In that study, weight loss, especially when achieved by calorie reduction plus exercise, significantly lowered serum estrogens and free testosterone in postmenopausal women.

Exercise might also boost the immune system or the body’s ability to clear cell-damaging free radicals, McCullough said.

For now, McCullough said her findings support what’s already recommended for good health. And they suggest that women might benefit even if they start exercising after menopause.

Sources: EurekAlert!, HealthDay News, Reuters Health