New research has shed light on the role exercise plays in fighting off cancer.
For years, doctors have linked physical activity with lower risks of breast and colon cancer. A number of studies show that light to moderate exercise actually reduces a number of side effects.
Scientists are beginning to understand the reasoning behind that link.
One new report by a leading British cancer charity reviewed the findings of 60 studies on the effects of exercise on cancer and found exercise significantly lowers the chances cancer will come back.
Exercising for just two and a half hours per week for prostate cancer patients lowered the recurrence risk by 30 percent. For breast cancer patients, it was 40 percent.
"We've seen that exercise can greatly impact the lives of people going through cancer therapy and also recovering from their treatment," Dr. Susan Schumer, a medical oncologist at the Vernon Cancer Center at Newton-Wellesley Hospital told Boston television station WCVB.
New research also shows the more fat cells a person has, the more insulin and estrogen they produce, both of which can help cancer cells grow.
"The activity can actually change the surrounding cells. It can change potentially surrounding estrogen levels, insulin and other chemicals that can serve like food for tumor cells," said Dr. Jennifer Litton, an oncologist with the University of Texas' M.D. Anderson Cancer Center.
Exercise also helps reduce stress, which may reduce inflammation.
Many doctors used to tell their patients rest was best, but these new findings are changing that advice.
"Remain active, but don't exercise or push yourself to the point of exhaustion," said Schumer. "That's going to really keep you healthy."