How exercise prevents cancer
HOW CAN ONE’S LIFESTYLE HELP PREVENT CANCER?
The 10 most common cancers in the country are breast (17.7 per cent), colorectal (13.2 per cent), lung (10.2 per cent), lymphoma (5.2 per cent), nasopharynx (4.9 per cent), leukaemia (4.4 ) per cent, uterus (4.2 per cent), liver (4 per cent), ovary (3.4 per cent) and stomach (3.3 per cent).
About 15 per cent of deaths are due to cancer. Lifestyle plays an important role in cancer and good lifestyle habit may prevent this disease. About one-third to half of cancer cases could be avoided if we maintain a healthy lifestyle.
The lifestyles factors are smoking, being physically inactive, obesity, bad diet and alcohol intake. All these are related to risk of getting cancers and heart diseases. A study in Canada showed that 40.8 per cent of cancer is due to lifestyle and environmental factors. The main lifestyle factors are smoking, physical inactivity and excess body fat, which account for 15.7 per cent, 7.2 per cent and 4.3 per cent respectively.
Physical activity plays an important role in preventing cancers. Many studies show that there are a few cancers which have inverse relationships with physical activity. Breast cancer and colorectal cancer are the two main cancers with strong inverse relationship with physical activity. Physical activity may reduce risk of breast and colorectal cancer by up to 50 per cent and 60 per cent respectively.
Other cancers are uterine, prostate and lung cancer. A recent meta analysis, published in The Journal of the American Medical Association in 2016 showed that there are 13 cancers with significant inverse relationship with physical activity. They are aesophageal adenocarcinoma, gall bladder, liver, lung, kidney, small intestine, gastric, endometrial, aesophageal squamous, myeloid leukaemia, myeloma, colon, head and neck, rectum, bladder and breast.
The more the exercise one does, the lower the risk of developing cancers. There is a dose-response relationship between exercise and its protective effects from cancers. The longer the duration of exercise and the higher the intensity of exercise, the more protection one gets against cancers.
High intensity exercise that burns 2,500 calories per week will reduce the risk of colon cancer by half. Four hours of physical activity per week at the intensity of six metabolic equivalents (like jogging) reduce the risk of breast cancer by 30-50 per cent.
HOW DOES THE BODY REACT TO PHYSICAL EXERCISE TO PREVENT CANCER?
Studies showed that physical activity may reduce the risk of cancers by many ways. It includes energy metabolism, sex hormone levels, influence of DNA repairs, insulin level and insulin sensitivity, systemic inflammation and effect on immune system.
Metabolism of sex hormone (oestrogen) in women has strong association with protective effects of breast cancer. Exercise reduces oestrogen level. This condition also reduces the risk of uterine cancer. Similarly, physical activity affects testosterone level in men, which has potential effects on reducing the risk of prostate cancer.
Exercise improves sensitivity of insulin receptor and improves glucose uptake into cells. The level of insulin will reduce. High level of insulin will stimulate cell proliferation and inhibit cells death, which increase the risk of cancer. The reduced level of insulin will reduce risk of colon, breast, uterus, prostate, pancreas and stomach cancers.
Exercise helps energy balance by reducing risk of excess weight and obesity. Obesity is associated with a number of cancers such as colon, breast, kidney and uterus cancers.
Exercise will improve systemic inflammation, which related to chronic disease and cancers. Pro inflammatory factors such as C-reactive protein will be reduced. Exercise induces normal cell growth and DNA repair, especially on intestinal epithelium will reduce risk of colon cancers. Immune system is also improved by exercise. It improves quantity and quality of natural killer (NK) cells. It will kill cancer cells.
There is also mechanical effect of exercise by reducing transit time of food, from gastric to rectum. It will reduce risk of colon cancer.
ARE PHYSICAL ACTIVITIES BENEFICIAL FOR CANCER SURVIVORS?
Patients diagnosed with cancer should be encouraged to exercise wherever possible. Physical activity is not only shown by research to protect against cancer, it also improves patients’ condition during cancer treatment and rehabilitation. Studies have shown that physical activity will improve the quality of life of patients. It will reduce side effects of treatment and improves fitness and general condition of patients.
The goal of exercise for patients with cancer includes maintaining good physical and social function, improves response to treatment, reduces symptom and side effect of treatment and prevents excessive weight gain. There is evidence that exercise may improve survival of patient with cancer, but the evidence is limited.
Benefits of exercise for cancer patients:
1. Improves fitness and reduces risk of heart disease.
2. Prevents weight gain and improves energy balance.
3. Improves balance and prevents fall
4. Reduces anxiety, depression and stress and improves self-esteem.
5. Reduces side effect of treatment such as fatigue, nausea.
6. Improves personal and social functions.
Patients are encouraged to exercise according to the general recommendation of exercise as mentioned by WHO — a minimum of 150 minutes of moderate intensity per week or 75 minutes per week of high intensity exercise, combined with two to three times per week of strength and resistance exercise.
Patients are also encouraged to do flexibility and balance exercises. However, they must exercise gradually from low intensity and shorter duration, and increase the dose over weeks or months. Always discuss with your doctor about your exercise routine. Always monitor for symptoms such as fatigue, pain, weakness or shortness of breath. In some situations, when the haemoglobin level is too low or other blood indices like white cells count or platelet count is too low, exercise may be contraindicated.
*An avid sportsman who believes in the healing powers of exercise, Assoc. Prof. Dr Ahmad Taufik Jamil is Universiti Teknologi Mara’s public health consultant and exercise physician. He can be reached at atjamil@gmail.com