Exercise is beneficial for our health in many ways. The obvious one is maintaining optimal body weight and improving the functioning of our cardiovascular system, but exercise was also shown to reduce the risk for postmenopausal breast cancer and according to the newest study, physical activity in adolescence and early adulthood may also reduce the chances for premenopausal breast cancer by as much as 23%.

Study looked at a group of 64,777 premenopausal women, aged 33 to 51 years, who filled in the questionnaire about their physical activity in the past years. They had to estimate average hours per week spent in strenuous, moderate, and walking leisure activity in different periods of their life, starting from the age of 12.

Women who are physically active are reducing their chances of premenopausal breast cancer, with the strongest association for those who were regularly exercising between the ages of 12 to 22 years. The next strongest association was between the ages of 23 and 34 years. "You don't have to be a marathon runner to get the risk-reducing effects of exercise," Dr. Colditz commented, as there were no huge differences between strenuous, moderate, and walking activities. However, another study suggested recreational activity had a greater effect than occupational or household activity.

Women, enjoying a 23% reduction in risk for premenopausal breast cancer, are running 3.25 hours or walking 13 hours per week (or engaging themselves in equivalent activities). Although there was no association for reduced risk for premenopausal cancer in women who took up exercise after the age of 35 years, physical activity during adulthood is known to reduce the risk for postmenopausal breast cancer.

The mechanism of how exercise protects against cancer isn't clear, although scientists believe it probably involves hormone levels and functioning. Exercise is thought to reduce women's exposure to estrogen which could be beneficial in this respect. Other explanations include changes in insulin-related factors and adipocytokines and modulation of inflammation and immune system.

These finding were also confirmed by a review of 62 studies, which was published on-line on May 13 in the British Journal of Sports Medicine. Almost half of the reviewed studies showed a dose depended relationship between exercise and the risk for breast cancer. Overall the risk reduction was about 25%.

Because there aren't many prevention strategies for premenopausal breast cancer, these findings have a big public health value. The strongest impact on reducing the risk is total average lifetime activity, that should be the greatest during ages of 12 to 22 years. Physical activity in young age therefore pays off in the long run. “This is just one more reason to encourage young women to exercise regularly," said the lead investigator, Graham Colditz.

Source: Exercise Protects Against Premenopausal Breast Cancer (Medscape)