How Much Exercise and When in Life?
Both moderate and vigorous activity were seen to have equal benefit in reducing breast cancer risks. Women who had been active throughout their life had the lowest breast cancer risk. Staying active after menopause had a greater effect as well. Some of the studies showed a dose-response effect -- the more exercise, the better.How Could Exercise Protect Against Breast Cancer?
The authors speculated that the mechanism by which physical activity protected against breast cancer was likely to be complex. It might involve effects on sex hormones, insulin-related factors, the immune system and other hormone and cellular pathways.Exercise Reduces Breast Cancer Risks for Younger Women
Regular exercise between the ages of 12 and 35 reduced breast cancer risks of developing cancer before menopause by 23%, according to the latest finding from the Nurses' Health Study II. This study tracks almost 65,000 women. "We don’t have a lot of prevention strategies for premenopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman’s risk of early breast cancer," said lead investigator Graham Colditz, M.D., Dr.P.H., in a press release.Previous studies showed that physical activity reduces postmenopausal breast cancer risk. There have been few previous studies showing that physical activity also reduces the risk of breast cancers diagnosed before menopause.
How Much Exercise is Needed to Reduce Risk?
The most active women in the study, who had the lowest risk, reported walking for 13 hours a week or running 3.25 hours per week. The intensity or particular sport did not matter, rather the total activity is what was linked to the reduced risk.Moderate and Vigorous Exercise Definitions and Recommendations
The Risks
A woman's chance of developing breast cancer in her lifetime is 1 in 8, with 185,000 new diagnoses each year in the US (1% of these are in men) and over 44,000 deaths each year. It is the most common cancer in women.
Sources
Friedenreich CM, Cust AE, "Physical activity and breast cancer risk: impact of timing, type and dose of activity and population subgroup effects." Online First British Journal of Sports Medicine 2008; doi:10.1136/bjsm.2006.029132
Maruit SS, Willett WC, Feskanich D, Rosner B, Colditz GA. "A prospective study of age-specific physical activity and premenopausal breast cancer." Journal of the National Cancer Institute. May 13, 2008.
