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Exercise is one of the most important actions you can take to help guard against many types of cancer. Up to one-third of cancer-related deaths are due to obesity and a sedentary lifestyle, including two of the most common cancers in the United States, breast and colon cancer.
Many people exercise to prevent heart disease, but exercise can also play a key role in preventing cancer. Most cancers are caused by lifestyle factors—not genes.
There are five accepted underlying mechanisms showing how exercise has cancer fighting properties:
Weight reduction: Although seemingly obvious, the observation that exercise helps to reduce weight among patients with cancer is supported by a large USA study, which reported a significant decrease in body fat after physical exercise counselling. Obesity is harmful because it increases the levels of circulating oestrogen and testosterone, two hormones linked to breast, uterine and prostate cancers. Even with medication to suppress oestrogen production, some oestrogen is stored in fat cells. Exercise helps by converting fat to muscle.
Blood fat levels:Regular exercise has been shown to help control the body´s levels of blood lipids and cholesterol independent of body weight. High serum fat levels have been particularly associated with a greater risk of a more advanced and aggressive type of cancer, with a higher possibility of relapse after initial therapy. Men with prostate cancer, with lower serum lipids, have better prognostic features including lower PSA, lower aggressiveness of cells (grade) and less advanced stage of the cancer. These factors correlate with better outcomes. A clue to the mechanism of fat levels, at least in prostate cancer, comes from the finding that lower serum fat levels correlated with lower testosterone.
Decreasing bowel transit time: Exercise decreases the time it takes for waste to pass through the bowel. Stagnant stools in the colon are thought to increase the risk of cancer by exposing the carcinogens that have not been absorbed in our diet to the mucous membrane of the bowel lining for longer. Patients who have developed one bowel cancer are more likely to develop a second. Reducing the carcinogen exposure time to the gut is likely, therefore, to be even more helpful in this higher risk group.
Immune pathway: An important component of immunity and healing involves the production of prostaglandins in the body. These are biologically active fats generated via the enzyme cycloxidase (COX). The COX-1 subtype is activated in response to trauma, infective or chemical injury, producing prostaglandins that contribute to the inflammatory response we are all familiar with following a wasp sting or healing from a skin cut, for example, leading to redness, swelling and pain. Unfortunately the prostaglandin pathways have also been hijacked by cancers. Those produced by the COX-2 subtype have been shown very sinister implications in the fundamental processes of cancer progression and spread. This includes aiding the formation of new cancer blood vessel (angiogenesis), encouraging cells to grow faster (proliferation), stopping cells from dying when they should (apoptosis) and encouraging them to lose their stickiness to the primary site, so they are more likely to invade other organs and spread elsewhere (metastasis). Obviously, scientists are endeavouring to develop drugs to block the COX-2 enzyme. It is our good fortune that exercise, as well as aspirin-like proteins found in fruit and vegetables, have been shown to inhibit COX-2 production providing one important mechanism of their direct anti-cancer benefit.
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