Exercise can help lower your risk of certain types of cancer, but sleep matters, too, say researchers at the National Cancer Institute. They reviewed data on nearly 6,000 women ages 18 to 65. In 1998, the women completed surveys about how much physical activity and sleep they usually got. Over the next 10 years, 604 women developed cancer. Physical activity was linked to lower cancer rates, but sleep pattern also mattered: Women who exercised for about an hour a day and got at least seven hours of sleep a night were 47 percent less likely to get cancer, but sleeping less than seven hours undid the cancer-fighting benefits of exercise.