In addition to keeping hearts healthy and bones strong, there's another reason why women may want to exercise regularly -- a new study published in the journal Cancer found a link between physical activity and reduced breast cancer risk.
A study of more than 3,000 women from Long Island, N.Y., found that women who engaged in 10 to 19 hours of at least mild exercise per week from their reproductive years on had about a 30 percent lower risk of developing breast cancer. The effects of physical activity were strongest among postmenopausal women, based on the data analysis.
The women were between the ages of 20 and 98 who participated in the Long Island Breast Cancer Study Project, a series of government-funded studies conducted to investigate possible environmental contributors to breast cancer on Long Island. The women were also predominantly white and upper middle class.
"We didn't see a risk reduction during the time before the first birth," said lead author Lauren McCullough, a doctoral candidate at the UNC Gillings School of Public Health. "There is a strong association seen with postmenopausal women, which is totally in line with other studies."
A separate study published in May by researchers at the Fred Hutchinson Cancer Research Center found that postmenopausal women who lose a moderate amount of weight through exercise and a healthier diet can lower their breast cancer risk because losing fat tissue can reduce the amount of two hormones associated with breast cancer.
McCullough and her colleagues found in their current research that weight also plays a role in the relationship between exercise and breast cancer risk. Gaining too much weight, it turns out, can eliminate some of the risk-reduction benefits of exercise after menopause.
Physically active women who gain more than 11 pounds after menopause are at a higher risk of developing breast cancer, though it's lower than for post-menopausal women who gain a similar amount of weight who don't exercise.
And obese women who exercised had about the same risk as normal-weight women who did no physical activity at all.
"For postmenopausal women, if you are physically active or highly active and maintain or gain just a little bit of weight, you are going to reap the benefits in terms of breast cancer reduction," McCullough said.
The study findings, McCullough added, are especially encouraging for post-menopausal women, since breast cancer tends to strike women who are older more often.
And she hopes if future research can confirm these findings, the data will someday lead to broader public health messages about the benefits of exercise.
"Trying to understand the relationship between physical activity and breast cancer will hopefully better tailor public messages to include cancer risk," she said. "Right now, recommendations from the Centers for Disease and Prevention and the World Health Organization about physical activity are based on risk reduction for cardiovascular disease."