Cancer – all causes Cancer is primarily caused by environmental factors. The most important are tobacco; diet, physical activity and factors related to diet, including body mass; and exposures (chemical, radiation) in the workplace and elsewhere. There is evidence that physical activity reduces the risk of breast cancer and lung cancer. The strongest evidence is for physical activity reducing the risk of colon cancer.
Obesity, which is often related to a lack of physical activity, is associated with several cancers.
A major international cancer study recommends that relatively sedentary individuals get an extra hour of moderate physical activity a day plus an hour of vigorous activity per week. Reference: “Food, Nutrition and the Prevention of Cancer: a global perspective”,1997, World Cancer Research Fund and the American Institute for Cancer Research
Physical activity has marked effects on the human body, which may influence overall cancer risk. These effects include direct mechanical processes such as improved circulation, ventilation and bowel transit time, improved energy balance and immune function and possibly the capacity to perform DNA repair.
Reference: “Physical activity and cancer risk: dose-response and cancer, all sites and site specific”, Inger Thune et al, Medicine & Science in Sports and Exercise, Vol. 33, No. 6, Suppl., 2001, pp. S530-S550
Cancer – breast Cancer of the breast is the most common cancer in women and the leading cause of cancer deaths in women worldwide.
The strongest evidence suggests breast cancer is linked to drinking alcohol, obesity and weight gain as an adult. Diets high in red meats, total fat and animal/saturated fat may increase breast cancer risk. The underlying biological reasons for breast cancer seem to be related to exposure to estrogen. For example, having no children, late age at first pregnancy and late menopause are established breast cancer risk factors. Exposure to ionizing radiation and inheriting specific gene mutations are other established risk factors but they probably contribute little to overall rates of breast cancer.
The most effective lifestyle means of preventing breast cancer are eating diets high in vegetables and fruits, avoiding alcohol, maintaining recommended body weight by proper diet and by regular physical activity throughout life. Reference: “Food, Nutrition and the Prevention of Cancer: a global perspective”,1997, World Cancer Research Fund and the American Institute for Cancer Research
Cancer – colon Cancer of the colon and rectum is the fourth most common cancer in the world.
Obesity, frequent eating, diets high is sugar, total and saturated fat, eggs and processed meats may increase the cancer risk. The underlying biological reasons for colorectal cancer seem to be related to development of growths (polyps) on the colon which become cancerous tissue. Inheriting specific gene mutations including a defective DNA repair gene, having colon problems (ulcerative colitis, infestation with a parasite) and smoking (which increases the risk of colon abnormalities) are other established risk factors.
The most effective lifestyle means of preventing colorectal cancer are eating diets high in vegetables, regular physical activity and low consumption of red and processed meat. Maintaining recommended body weight and eating a diet high in complex carbohydrates and low in sugar, fat and eggs may provide additional protection.
Cancer – lung Cancer of the lung is the most common cancer in the world and causes the most cancer deaths in the world overall.
The overwhelming cause of lung cancer is smoking tobacco. A lifetime smoker has a risk some 2000% to 3000% that of a non-smoker.The most effective lifestyle means of preventing lung cancer is to avoid tobacco smoke.
Physical activity may provide some protection against lung cancer but the evidence is much weaker than the benefit of a healthy diet. Remember that even if physical activity reduces the risk of lung cancer for a smoker by 50%, the risk is still very high.
Diets high in fruits and vegetables provide the most effective dietary means of preventing lung cancer. However, even smokers whose diet are protective remain at high risk.
Death – all causes Compared to people who are active, sedentary people experience up to a 2 to 5 fold increase in the risk of dying early. The strongest link to prevention of premature death is objectively measured physical activity (fitness, treadmill performance and other things which can be measured). The link is weaker between preventing early death and only self reported activity (what people say they do).
For healthy men (aged 20-82 years), who were initially at low levels of fitness, increasing their fitness level resulted in about a 60% reduction in their risk of premature death. Other studies have indicated that moderate and vigorous levels of activity were equally protective at age 50. The protective effects of high levels of activity lasted until age 70 but the protective effects for moderate activity lasted beyond age 80.
Reference: “Physical Activity and Health: A Report of the Surgeon General”, US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996, S/N017-023-00196-5, Chapter 4, p86
Diabetes – Type 2 Diabetes is a group of disorders that results in high blood sugar. Type 1 diabetes is marked by an inability to produce insulin in the body. This affects about 10% of persons with diabetes. The vast majority of people with diabetes have Type 2 which is characterized either by elevated insulin levels that are ineffective in normalizing blood sugar levels (decreased sensitivity to insulin) or by impaired insulin production or by a combination of these. Risk factors for Type 2 diabetes include genetic factors and age but important risk factors for insulin resistance such as obesity can be modified.
Societies that have discontinued their traditional lifestyles (which presumably included large amounts of physical activity) have experienced large increases in Type 2 diabetes. There is particular concern in many Canadian aboriginal communities about the high incidence of this late onset diabetes.
Because insulin problems affect overall health, diabetes is associated with many other diseases such as heart attack, stroke and heart failure. Amputations may result from complications of diabetes.
A symposium in Ontario in October, 2000 considered a variety of scientific papers on the benefits of physical activity. It concluded that there was strong evidence that vigorous physical activity protected against development of Type 2 diabetes. There was also evidence that for Type 2 diabetics, physical activity was important to reduce risk of heart attack and related diseases and to prevent premature death.
Reference: “Dose-response issues concerning physical activity and health: an evidence based symposium”, Y. Antero Kesaniemi et al, Proceeding for symposium held October, 2000, Ontario, “Medicine & Science in Sports and Exercise” 0195-9131/01/3306-0351
Heart Disease Cardiovascular disease which includes heart disease and stroke is a leading cause of death and disability. Major studies indicate that moderate levels of physical activity and fitness provide protection against cardiovascular disease and that this protection increases with increasing levels of physical activity and fitness. Avoiding tobacco use, obesity and excessive stress and following a healthy diet will also reduce your risk.
Physical activity, even for those suffering from advanced heart disease, has been shown to improve blood flow to the heart and promote other changes which reduce the risk of heart rhythm disturbances and sudden death.
Reference: “Physical Activity and Health: A Report of the Surgeon General”, US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996, S/N017-023-00196-5, Chapter 4, p87, p110-112
Heart disease is almost unknown in societies that feature regular physical activity, vegetable-based diets and smoke-free environments. Such disease was very uncommon in America until the industrial revolution. Heart attacks were not described in American medical literature until 1912. Recent studies found shocking evidence that heart disease is now starting in childhood. A study of children and young adults who died in accidents found that all had fatty streaks in their largest artery by the age of 15 and about half had fatty deposits in their arteries by age 19. A second study found that 80% of young adults (average age 26) had some of the arteries that supply blood to the heart were blocked and 20% had blockages that narrowed other arteries by half.
Reference: “Conquering Heart Disease: new ways to live well without drugs or surgery”, Harvey B. Simon, M.D.; Little, Brown and Company,1994, p27
Impotence Male impotence is frequently seen in patients with heart disease. A study has shown that high levels of cholesterol in the blood and low levels of protective blood components (HDL’s or High-Density-Lipoproteins) are important indicators for erectile dysfunction. Physical activity has been shown to be preventative for heart disease, to reduce blood cholesterol levels and improve HDL levels in blood. While there are indications that physical activity will be protective, there is not sufficient data to determine a relationship between physical activity and fitness to male impotence.
Reference: “Total cholesterol and high density lipoprotein cholesterol as important indicators of erectile dysfunction”, Wie M et al, American Journal of Epidemiology, 1995 Dec 1;Vol. 142, No. 11, pp. 1246-7
Living Restrictions Quality of life for an older person is affected by the person’s ability to live independently. Resistance training is important because it helps to maintain or improve strength essential for daily living and it helps reduce the risk of injury from falls. Improvements in daily living activities are associated with increasing levels of energy expenditure. The most consistent evidence is that regular physical activity postpones disability and promotes independent living in the elderly.
Reference: “Dose-response issues concerning physical activity and health: an evidence based symposium”, Y. Antero Kesaniemi et al, Proceeding for symposium held October, 2000, Ontario, “Medicine & Science in Sports and Exercise” 0195-9131/01/3306-0351
Mood Disorders Individuals with higher levels of physical activity are less likely than those with lower levels to develop depressive illness. Aerobic exercise training for 6 – 12 weeks in mild to moderate depression and anxiety is consistently associated with an improvement comparable to that from anti-depressant medications although with a slower response.
Reference: “Dose-response issues concerning physical activity and health: an evidence based symposium”, Y. Antero Kesaniemi et al, Proceeding for symposium held October, 2000, Ontario, “Medicine & Science in Sports and Exercise” 0195-9131/01/3306-0351
Weight Control Obesity is a major health problem in Canada. It plays a critical role in the development of diabetes (Type 2) and increases risk for heart disease, high blood pressure, arthritis, various cancers and death from all causes.
The height – weight index called Body Mass Index (BMI) is not a perfect measure of obesity since it can not distinguish between weight which is fat and weight which is muscle but increasing BMI is consistently associated with increasing rates of premature death.
Many adults are overweight but there is increasing concern about the growing number of overweight children. Overweight children are likely to become overweight adults at increased risk for many health problems.
Although the rate of weight loss from increased physical activity alone is quite slow, the combination of physical activity and dieting is more effective for weight control than dieting alone.
Fat is the main energy source during rest and mild intensity exercise. Generally when you are exercising with enough intensity to cause heavy breathing, your body has already switched from burning fat to burning carbohydrates. If burning fat is an important objective, you will want to choose low to moderate activities which you can perform for long durations.
Reference: “Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids”, Institute of Medicine, 2002, Washington, DC: National Academy Press, Chapter 12, p12-24 to 12-27
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