Cancer, on the other hand, is a general term for diseases in which abnormal cells divide and grow unchecked. The resulting mass or tumor has the potential to spread through the bloodstream and lymphatic system and establish growth in other parts of the body when they become malignant.
The signs and symptoms of cancer will depend on the site, its size and how much it affects the surrounding organs or structure. When it spreads, its symptom may appear in different parts of the body.
General symptoms and signs of cancer include unexplained weight loss, fever, fatigue, pain and skin changes. Specific symptoms due to site range from change in bowel habits or bladder functions as in colorectal and prostate cancers; sores that do not heal on the penis or vagina, unusual bleeding or discharge from the cervix and breast nipple; a thickening or lump in the breast or other parts of the body like testicles, lymph-nodes and soft tissues of the body; indigestion or difficulty in swallowing in cancer of the esophagus, stomach and pharynx; recent change in a wart or mole in melanoma and nagging cough or hoarseness of voice in cancer of the lung, larynx or thyroid.
The relationships between physical activity and cancers have been extensively studied over decades. Most of these epidemiological studies have compared the physical activity levels of people who have or develop cancers and those who do not. Cohort studies have been used to follow populations forward in time to observe how physical activity habits affect cancer occurrence and mortality.
Groups of patients who have cancers and separate groups who do not have cancers, have also been asked to recall their previous physical activity in case control studies.
In some cases, cross sectional studies have been used to assess the relationship between physical activity and disease at the same point in time.
And in more interesting situations, clinical trials are done in which physical activity patterns are altered in other to assess whether cancer occurrence amongst other diseases is modified as a result of this alteration has been carried out.
Evidence has shown that for people who do not smoke, a healthy diet and physical activity are the most important ways to reduce cancer risk. According to the American Cancer Society, “about 550,000 cancer deaths that occur in the United States each year are due to an unhealthy diet and insufficient physical activity. Therefore it has been suggested that adults should be moderately active for at least 30 minutes five or more days per week. For reducing the risk of breast cancer and colon cancer, even more exercise may be better.”
Various mechanisms have been suggested in the reduction of cancer risks due to physical activity. The pathophysiology of breast cancer for instance, have been traced to estrogen hormone. Epidemiological risks studies have therefore found that moderate physical activity influences estrogen metabolism thereby reducing breast cancer risks.
A prospective study and another case control study in the United States also showed that increased physical activity may lower the risk of ovarian cancer by reducing the frequency of ovulation, decreasing body fat and diminishing chronic inflammation.
In a similar study, there was a report of reduction of the risk of prostate cancer by as much as 10 to 30% among men who did exercise regularly. Exercise modulates hormone levels and obesity, enhances immune function and reduces oxidative stress--these are believed to be mechanisms that may underlie the protective effects of exercise.
Similarly, physical activity has been shown to reduce the risk of colon cancer by increasing gut motility, or spontaneous movement; enhancing the immune system; decreasing insulin and insulin-like growth factor levels; decreasing obesity; enhancing free radical scavenger systems. It has been estimated that 12-14% of colon cancer could be attributed to the lack frequent vigorous physical activity.
It is interesting to note that physical activity not only prevents cancer. It also reduces case fatality and increases the quality of life in cancer patients (14) For example, the North Karelia project was started in Finland to prevent non-communicable diseases in collaboration with the community, health sector, food industry and mass media. It focused on healthy diet, physical activity and reducing smoking. The success of the project which has spanned 25 years indicates reduction of the age-adjusted mortality rate of men 25 to 64 years old; cardiovascular deaths fell by 73%, lung cancer by 71% and total mortality by 49%.
It is important to bear in mind that in the analysis of heritable and environmental causes of cancers, genetic factors are believed to explain only 5% of all cancers. Genetic makeup therefore provides only the foundation while in many instances environmental conditions provide the trigger for a multi-staged process to unfold. The process, however, is enhanced in individuals who live a sedentary life.
In conclusion, without any shade of doubt, enough scientific evidence abounds to prove that regular physical activity as a main determinant of energy expenditure reduces the risk of cancers. Therefore there is need for more community-directed health education to increase awareness concerning the benefits of physical exercise in the primary prevention of cancers.
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