In a study of 123,000 people, Patel found that the more time people spent sitting, the higher their risk of dying early. ???Even among individuals who were regularly active, the risk of dying prematurely was higher among those who spent more time sitting,??? she said. Even if you are doing half an hour of aerobic activity a day, you need to make sure you don't sit the rest of the day, Patel said. ???You have to get up and take breaks from sitting.???

James Levine, a professor of medicine at Mayo Clinic in Rochester, Minn., says many people sit an average of seven to 9 and half hours a day. ???If you've sat for an hour, you've probably sat too long,??? he said. ???A brisk daily walk of at least 30 minutes could lower a person's risk over time for breast cancer and colon cancer,??? says Alice Bender, a registered dietitian with AICR.

Friedenreich said looking into why exercise reduces cancer risk she found some clues. In a study of 320 post-menopausal women, she has found that physical activity appears to decrease the risk of cancer by increasing insulin sensitivity and reducing body fat, inflammation, metabolic hormones and sex steroids hormones.