It is never easy to prove that specific lifestyle choices really do deliver tangible benefits in terms of preventing illness, because there can be a great many confounding factors causing casual interference when this is studied. Exercise is no exception, and yet several epidemiological studies have actually managed to provide evidence that being physically active is useful to prevent specific kinds of cancer. Before going into which types of cancer, it is worth understanding how exercise helps prevent cancer in general.
Researchers have figured out how physical activity affects some of the body’s key mechanisms, such as metabolic processes - energy and hormones, inflammation, and the immune system.
Exercise helps you stay fit, it keeps your musculoskeletal and circulatory systems young, and facilitates weight loss. We don’t need scientific studies to tell us this, personal experience is enough. However, sports and all physical exercise have other hidden benefits, which researchers are now able to study in detail and which also explain how these activities prevent cardiovascular disease and cancer.
First of all, it is worth distinguishing between two types of physical activity: aerobic exercise (which kicks in after about 3-4 minutes of vigorous exertion and stabilises after 20), in which muscle tissue uses oxygen to synthesise ATP, the molecule that provides energy for numerous physiological processes; and anaerobic exercise, in which ATP synthesis occurs without using oxygen.
Anaerobic exercise trains and strengthens muscles, but the heart rate doesn’t accelerate. It is therefore less effective in preventing illness, particularly cardiovascular disease.
Regular aerobic activity, on the other hand, helps reduce the body mass index and in so doing indirectly prevent forms of cancer related to being overweight and obese. Increased blood flow oxygenates the tissues, this also facilitates the capillary distribution of natural anti-inflammatory substances. Inflammation, especially when it is chronic, favours cell mutations and the consequent transformation of healthy tissue into cancerous tissue.
Improved blood flow allows the toxic substances that accumulate in the body to be removed more efficiently. This process also takes place in the lungs, which are dense with blood vessels, and their function is precisely that of oxygenating the blood and eliminating waste gases such as carbon dioxide.
Physical exercise accelerates intestinal transit time. This is important because the longer waste substances from food remain in contact with the mucous membranes of the stomach and bowel, the greater the risk of any toxic or mutagenic compounds damaging the cells. The fact that it speeds up the transit time of food in the gastrointestinal system is considered one of the main reasons why exercise prevents colon cancer.
Constant, moderate exercise reduces the concentration of certain hormones (including oestrogen), which some types of cancer are sensitive to (such as cervical and breast cancer). In addition, sport increases the sensitivity of body tissue to insulin and decreases its release into the bloodstream, facilitating the immediate use of sugars. Although insulin is an essential hormone for the body, too high a concentration in the bloodstream stimulates inflammation and facilitates tumour growth. This is precisely why, when talking prevention of disease by means of a healthy diet, it is always recommended to eat foods with a low glycaemic index, i.e., those that raise the level of insulin in the blood more slowly.
Lastly, physical activity stimulates the immune system by regulating the number and activity of certain essential cells, including macrophages and “natural killer cells” (lymphocytes), involved in cancer.
The effects of physical activity on colon cancer are the most widely studied. The findings of great many specific, high-quality studies highlight how the risk of becoming ill decreases in proportion to the intensity, duration, or frequency of exercise. Some studies estimate that active people have a 30-40 percent lower risk of developing this type of cancer than sedentary people. For maximum benefits, 30-60 minutes of vigorous physical activity are needed per day (such as running at a brisk pace), but less strenuous activity will also yield proportionate benefits as long as it is done on a regular basis. The protective effect of exercise has been conclusively demonstrated for colon cancer, while the same level of unequivocal evidence is still lacking where rectal cancer is concerned. It is known, however, that regular exercise reduces body mass, and obesity is an important risk factor for this type of cancer; moreover, the length of time that waste substances are in contact with the internal wall of the intestine also decreases due to physical activity, thus reducing the potentially toxic and inflammatory effects of these substances.
What about breast cancer? Here, too, studies are available from all over the world and the results are quite clear: frequent physical activity, even of moderate intensity, reduces the risk of developing this type of cancer. Some research has also looked into what happens to women who begin exercising after the menopause, which is when they are most at risk of falling ill. Again, the results show that there are benefits in terms of reducing the risk when compared with women who remain sedentary. In general, half an hour of vigorous exercise every day, (such as running) seems sufficient to activate the protective mechanisms.
Although there are fewer studies on endometrial cancer, the ones available also demonstrate that potentially there is a 20 – 40 percent reduction in the risk of developing this form of cancer, in proportion to the intensity and frequency of physical activity. The effect is due to weight reduction and the consequent decrease in levels of female hormones. These benefits apply to people of all ages.
Some studies have focused on lung cancer. In this case it would appear that physical activity reduces the risk of this disease by about 20 percent, but it is not able to counteract the negative effects of smoking, especially in women.
Lastly, there are numerous studies on prostate cancer that have not yet been able to demonstrate that exercise significantly reduces the risk of falling ill. Researchers suggest that physical activity may indeed have a positive effect, since this type of cancer is sensitive to hormones, which are reduced by regular exercise. However, prostate cancer is a heterogeneous disease, and this may be why researchers have not yet come to a definitive conclusion on the protective role of exercise.
The scientific community is still investigating whether physical activity can also help prevent many other types of cancer.