This much is known: A sedentary lifestyle raises the risk of cancer, while physical activity – even moderate exercise – can reduce the risk not only of developing cancer but having a recurrence following treatment. What’s not so clear is exactly why.
“It’s still a little unknown,” says Dr. Jeffrey Meyerhardt, co-director of the Colon and Rectal Cancer Center at Dana-Farber/Brigham and Women’s Cancer Center, who has studied the relationship of exercise and colorectal cancer risk. In a previous study, he and Charles Fuchs, MD, MPH, director of the Gastrointestinal Cancer Center, reported that in patients with stage III colorectal cancer, more physical activity was associated with a lower risk of cancer recurrence and mortality.
According to Dr. Meyerhardt and other researchers, one way exercise can influence cancer risk is by lowering the amounts of insulin and insulin-like growth factors in the bloodstream. These hormones stimulate tumor cells to spread and survive despite the body’s attempts to kill abnormal cells. Studies show physical activity can directly reduce insulin levels, and research on this link is continuing. Jennifer Ligibel, MD, a Dana-Farber/Brigham and Women’s Cancer Center oncologist and director of the Leonard P. Zakim Center for Integrative Therapies, led a study in breast cancer patients that showed that participation in an exercise program led to a reduction in insulin levels in previously inactive breast cancer survivors.