A review of 170 animal and human studies shows that regular exercise is associated with reduced cancer risk, particularly for the types of cancers that are associated with unhealthful lifestyles, such as those of the breast, colon, prostate, lung and endometrium (J Nutr, 2002 Nov;132(11 Suppl):3456S-3464S). Exercise helps to prevent cancer by reducing causes of inflammation: overweight, excess calorie intake, high blood sugar, high insulin and insulin-like growth factor-1, high estrogen, and overactive and depressed immune function.
The most likely reason why exercise reduces cancer risk is that it reduces an overactive immunity (Exerc Sport Sci Rev, 2015;43(3):134-142). Many studies show that exercise reduces markers of an overactive immune system that are also necessary for cancer growth: interleukin-6, tumor necrosis factor-a, and monocyte chemoattractant protein 1.
• Exercise was shown to reduce inflammation that caused mice to develop colon cancer (Int. J. Oncol, 2014; 45(2):861–8) and breast cancer (Cytokine, 2011; 55(2):274–9).
• Exercise helped to prevent breast cancer in rats (Cancer Prev. Res (Phila), 2012; 5(3):414–22) and mice (Cytokine, 2011; 55(2):274–9).
• Exercise reduced inflammation in humans to increase survival from colon cancer (Gut, 2006; 55(1):62–7).
• Exercise is associated with reduced pre-cancerous polyps in humans (BMC Res Notes, 2012; 5: 312).
If you do not exercise, I recommend that you start an exercise program that may protect you from certain cancers and will also help to protect you from obesity, diabetes and heart attacks. Be aware that exercise can cause heart attacks in people who already have blocked arteries, so check with your doctor, particularly if you have any markers for arteriosclerosis: high blood pressure, cholesterol or blood sugar, or a lot of belly fat (more than three inches when you pinch the skin over your belly).
Start out Slowly
If you haven't exercised for a while, just go out every day and walk, jog or cycle for a short time, until your legs start to feel heavy or sore, and then quit for the day. Try to do this every day, but take days off when your legs feel sore. As you continue to move a little each day, you will gradually be able to increase the time you can spend exercising until you are able to exercise at low intensity every day for 30 minutes without feeling sore.
Now You Can Start to Pick Up the Pace
Fitness requires some degree of intensity. Whenever I see people reading while walking on a treadmill, I just shake my head. You have to damage muscles to make them larger and stronger, and you have to get short of breath to increase your ability to take in and use oxygen.
On the first day, warm up by walking, jogging or pedaling at a very slow rate for five to 10 minutes. Then gradually pick up the pace and when your legs start to burn, hurt or feel heavy, slow down. Do not use a clock, but when your legs feel recovered, pick up the pace again. Slow down at the least sign of discomfort. Do this until your legs start to feel heavy or tired and then quit for the day.
On the next day just go very slowly, or take the day off if your legs feel unusually sore.
Try to establish a training regimen in which on one day, you take a harder workout by alternating intervals of slow and fast movement, and on the next day, you go slow. Try to exercise for about half an hour each day. These alternating stress-and-recover workouts can make you very fit, help to prevent disease and prolong your life.
• Most people need to allow 48 hours between intense workouts. Take more recovery days if you need them.
• Your legs should feel a little sore when you wake up each morning. They will usually feel sore when you start your workout also. If your legs still do not feel fresh after you warm up by exercising slowly for five to 10 minutes, take the day off.
• If you feel pain in one spot that increases with exercise, stop the workout immediately and take the rest of the day off. Your body is telling you that you are headed for an injury if you continue to exercise.
• A review of more than 50 studies showed that exercise can reduce risk of colon cancer by 30 to 40 percent, and those who were most active gained the greatest protection (Sports Medicine, 2004; 34(4): 239–252).
• More than 60 studies showed that women who exercise are 20 to 80 percent less likely to develop breast cancer (Cancer Epidemiol. Biomarkers Prev, 2006; 15(1):57–64).
• Time spent sitting is associated with increased breast cancer risk (Breast Cancer Res. Treat, 2011; 130(1):183–94).
• More than 20 studies showed that women who exercise have a 20 to 40 percent reduced risk for cancer of the inner lining of the uterus (Cancer Epidemiology and Prevention, Oxford University Press, 2006).
• A review of 21 studies showed that exercise reduces risk for lung cancer (Cancer Causes and Control, 2005; 16(4):389–397).
• In a review of 36 studies, most found an association between exercise and reduced risk for prostate cancer (Archives of Internal Medicine, 2005; 165(9):1005–1010).
• Exercise increases survival rate in breast cancer (JAMA, 2005; 293(20):2479–2486) and colorectal cancer (Journal of Clinical Oncology, 2006; 24(22):3527–3534).