The exact causes of cancer are widely unknown. The risk factors for acquiring certain cancers are clear, however, and will be listed below.
Risk factors do not exist in a vacuum. They are complex and numerous. They interact with each other, and any one or a combination of many can trigger a cell mutation that eventually becomes a malignant tumour.
In addition, a common feature of the development of cancer is the lengthy period, often over many years, between subjection to a carcinogenic agent (a cancer causing substance) and the emergence of a recognizable cancer. The most likely reason for this silent, or "latent" period is that the carcinogenic agent does not itself, in one step, cause the cancer. Rather, it leaves that cell(s) more vulnerable to further mutations by other cancer causing agents.
A cell or cell mass with a sufficient number of mutations, or "hits", may then outgrow its neighbouring tissue and form into a tumour. This tumour can then be subjected to cell duplications and even further mutation, eventually growing to the extent that it invades surrounding tissue and metastasizes to other organs. In other words, it takes several attacks by several invaders over the course of a lengthy period to trigger a cancerous growth. This is why it is so difficult to pinpoint the exact causes of the disease.
Risk Factors
Age
For most cancers, incidence is quite rare under the age of thirty. That number rises exponentially and dramatically with age. For instance, while cases of prostate cancer are virtually non-existent in men under 40, autopsies reveal that most men over 80 have some degree of prostate cancer even though their deaths resulted from unrelated reasons.
Some experts believe that prostate cancer, as well as other cancers, are natural diseases of aging (though some cancers are extremely rare in some parts of the world). The best known explanation for the relationship between increased age and cancer is the lengthy time it takes for cells to mutate to the extent where a cancer is formed.
It is estimated that anywhere from three to seven of these mutations are required to form a recognizable cancer -- a process that may take several decades. Furthermore, with increased age comes reduced immune capacity, leaving your body more susceptible to damage by carcinogenic agents. Not all cancers are more prevalent with increased age. Testicular cancer, for example, shows a peak incidence between ages 20 and 50 before declining with older age. Cancers of the nervous system and leukemias are not only prevalent in old age but also during early childhood.
Heredity
Tumour growth can be promoted by a family history of cancer. You and your naturopath or other health practitioner should always be more wary of your cancer risk if family history is involved. However, it is estimated that only 2% of all cases of cancer are caused directly by heredity. Studies linking heredity to cancer risk are often misleading and exaggerated. It is important to remember that families share environment and lifestyle just as much as they do genes; lifelong bad habits (such as poor diet and exercise) and environmental conditions (such as smoking and other pollutants) that expose you to greater risks of cancer are more often than not learned and shared at home.
Diet
Diet is the most important risk factor for cancer. A diet high in both saturated and unsaturated fats and low in fibre appears to play a significant role in the development of cancers of the colon, rectum, prostate, testes, breast, uterus, and gallbladder. Several studies have shown that countries that consume higher quantities (per individual) of dietary fats and meats also have higher incidences breast, prostate, and colon cancer. Studies have also shown that diet conscious vegetarians have a lower general incidence of all types of cancer.
Although it is difficult to pinpoint the exact variables that cause the disparities in cancer incidence rates between certain countries (as there are plenty of other differences such as environmental conditions, age distribution, and the many lifestyle factors that also affect cancer risk), it is clear that the incidence of some cancers at a given age in different parts of the world varies at least ten, or possibly a hundred, fold.
African Americans, for example, have cancer incidence rates resembling those of Americans in general. However, the Black population of West Africa, from which the large majority of African Americans were originally drawn, has an incidence rate of colon cancer ten times lower than do African Americans.
Similar studies have been carried out on Japanese settlers in the United States. Although incidence rates of certain cancers amongst Japanese people living in Japan are relatively low, Japanese Americans, whose families have lived in the United States for three generations, display cancer incidence rates similar to those of the greater American population. The American diet, when compared to that of the Japanese, contains 10 times more animal protein and 3 times more dietary fat. It is suspected that the rise in cancer incidence rates amongst Japanese Americans is strongly associated with assuming the high-fat, low-fibre American diet.
Eating preserved foods, especially smoked or nitrate-cured meats, increases your risk of cancers of the esophagus and stomach. Poor dietary habits in general weaken your immune system, impairing your body's own cancer preventing capacities. Furthermore, poor dietary habits expose your body to damage by free radicals. Free radicals are negatively charged atoms or compounds that usually occur in pairs. However, free radicals are chemically unstable when they occur individually and readily join to other compounds. This can cause cell mutation and promotes potentially cancerous growths.
Dangerous levels of free radicals in your body (they occur naturally in smaller amounts) can occur as by products of breaking down excess fats, especially fats that have been cooked at high temperatures. Exposure to x-rays and to other environmental pollutants also promotes the creation of free radicals. Antioxidants, such as vitamin A, C, and E, selenium, and alpha-lipoic acid neutralize free radicals by bonding to their unstable electrons (see dedicated section on Antioxidants for further detail). A diet low in antioxidant intake can further subject your body to free radical damage.
Environmental Carcinogens
Exposure to coal products, benzene, cadmium, uranium, asbestos, and nickel increase the risk of developing cancer. Excess exposure to ultraviolet radiation can occur even on cloudy days, and can promote skin cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma.
Obesity
In men, obesity is linked to colon and rectal cancer; in women, it has been linked to gallbladder, cervical, uterine, and breast cancer. This may be due to hormonal imbalances but is widely attributed to diet, lack of exercise, and lifestyle.
Sexual Practices
Sexual history seems to be linked to both the prevention and promotion of certain cancers. In men, a history of venereal disease and the use of testosterone to treat impotence are both risk factors for prostate cancer. And although the subject is highly controversial, some experts say that men who have had vasectomies are also at greater risk of developing prostate cancer.
In women, having intercourse before age 18 increases the risk of cervical and uterine cancer. Oral contraceptives and estrogens have been linked to both breast and uterine cancer. Childbearing reduces the risk of cancers of the ovary, uterus, and breast, while giving birth before age 30 reduces the risk of developing cancer later in life. Your risk of breast cancer can increase if your first childbirth was after age 35, or if you have had no children.
Multiple sex partners, for both men and women, exposes you to greater risks of sexually transmitted diseases, which can cause cancers of the head, neck, cervix, penis, and anus, as well as AIDS and AIDS-related cancers.
Stress
Stress is closely linked to many disorders, including obesity, cardiovascular disease, high blood pressure, insomnia, headaches, and many other illnesses. Although it is still unknown whether stress is related to cancer, it may play a significant role in suppressing immune function, leaving your body more vulnerable to attacks by cancerous agents.
Tobacco and Alcohol
Smoking is second only to diet as the most important risk factor for cancer. In fact, smoking and dietary habits account for about two thirds of total risk for all types of cancer. Despite the ongoing claims by the tobacco industry, there is no longer any doubt that smoking is directly related to lung cancer.
In the early 1900s, before smoking became widespread, lung cancer was a rare disease. In 1950, when the first report on the causal relationship between smoking and lung cancer was published, there were 1,220 lung cancer deaths in Canada. By 1985, that number had risen to 11,424. Today, although the death rate has started to decrease in men, lung cancer is rapidly overtaking breast cancer as the leading cause of cancer deaths in women.
Excess alcohol consumption is linked to cancers of the head, neck, larynx, and possibly the liver and pancreas. Alcohol consumption has a strong relationship with smoking, a combination that greatly increases your risk of cancers of the mouth, throat, and esophagus.
Viruses and Other Diseases
Cancer-causing viruses are called oncogenic viruses, and act by directly sabotaging cellular function. Epstein-Barr virus (EBV) is common and can cause nasopharyngeal cancer and is associated with lymphomas (but more so in the Far East and in Africa). Hepatitis B virus and Human Papilloma Viruses (HPV) are both known to be cancer inducing. There is a strong relationship between the Human Immunodifficiency Virus (HIV) and the development of AIDS-related cancers such as Kaposi's sarcoma, a type of skin cancer. All viruses and diseases that tend to suppress immune function, especially AIDS, can increase your risk of developing cancer.
