DIETS AND EXERCISE AS CAUSES OF CANCER
Diets, physical inactivity and obesity are related to approximately 30-35% of cancer cases. In the United States, excess body weights associated with the development of main types of cancer and a factor 14-20% of all cancer death. Physical inactivity is believed to contribute to cancer risk not only through its effect on body weight but also through a negative effect on the immune and endocrine system. Diets that are low in vegetable, fruit and whole grains and high in a process or red meat are linked with a number of cancers. A high salt diet is linked to gastric cancer aflatoxin B1, a frequent food contaminates with liver cancer.
INFECTION And the CAUSES OF CANCER
Viruses that cause cancer are called oncovirus (cervical carcinoma). Epstein-Barr virus (B-cell lymph proliferative disease and nasopharyngeal carcinoma) and human T-cell leukaemia virus (T-cell leukaemia).
Radiation can cause cancer in the most part of the body in all animals and at any age, although radiation-induced solid tumours usually take 10-15years and up to 40years to become clinically manifest and radiation-induced leukaemia typically require 2-10years to appear (john 2000). Unlike chemical or physical triggers for cancer, ionising radiation hits molecules within cells randomly.
Less than 0.3% of the populations are carriers of a genetic mutation which has a large effect on cancer risk (Roukos, 2009). They cause less than 3-10% of all cancers.
Some substances cause cancer primarily through their physical, rather than chemical effects on cells (mailtoni, 2002). A prominent example of this is prolonged exposure to asbestos fibres. Asbestos is a normally occurring, fibrous rock that causes mesothelioma, a type of lung cancer. Other substances in this category include both naturally occurring and synthetic asbestos-like fibres, such as wollastonite, attapulgite, a glass of wool and rock wool, are believed to have similar effects. Nonfibrous particulate materials that cause cancer include powdered metallic cobalt and nickel, and crystalline silica.
Some hormones cause primarily by encouraging cell proliferation (Henderson 2002). Hormones are the important cause of sex –related cancer such as cancer of the breast endometrial, prostate, ovary and testis and also thyroid cancer and bone cancer.
Cancers pathogenesis is traceable back to DNA mutation that impact cell growth and metastasis. Substances that cause DNA mutations are known as mutagens and mutagens that cause cancer are known as carcinogens. Particular substances have been linked to specific types of cancers. Tobacco smoking is associated with many forms of cancer (sasco 2004) and causes 90% of lung cancer.
Many mutagens are also carcinogens, but some carcinogens are not mutagens. Alcohol is an example of a chemical carcinogen that is not a mutagen (seitz 1998). Such chemical may promote cancer through stimulating the rate of cell division. Faster rate of replication leaves less time for repair enzymes to repair damaged DNA during DNA replication, increasing the likelihood of a mutation.