Women who regularly exercise before or after menopause have a considerably reduced risk of breast cancer, but gaining a lot of weight could undo all that effort.
Other studies have looked at the benefits of exercise on breast cancer survival and prevention. But this quantifies the amount and type of activity women may need to make a difference in the risk of developing breast cancer.
The study, published online today in the journal Cancer, focused on 1,504 women with breast cancer, both invasive and non-invasive, and 1,555 women who didn’t have the disease. The subjects ranged in age from 20 to 98.
Researchers found that exercising from 10 to 19 hours per week was linked with a 30 percent drop in breast cancer risk. That risk reduction was seen in women who exercised at all levels, from mild to vigorous, compared to women who exercised very little or not at all.
Being active was also effective in decreasing the chance of developing hormone receptor positive breast cancer. That type of cancer has tumor cells with receptors for estrogen or progesterone or both. When hormones attach to them, it can cause those cancer cells to grow. The University of Maryland Medical Center says that about 75 percent of all breast cancers are estrogen receptor positive, and about 65 percent are also progesterone receptor positive.
The study also found that being active isn’t enough. Gaining a substantial amount of weight, even while active, was associated with higher risk of developing breast cancer, especially after menopause.
“The observation of a reduced risk of breast cancer for women who engaged in exercise after menopause is particularly encouraging given the late age of onset for breast cancer,” said lead author Lauren McCullough in a news release. McCullough is a doctoral candidate at the University of North Carolina Gillings School of Global Public Health.