Chemical and environmental factors, including diet and lifestyle, may be responsible for causing 80 to 90 percent of all cancers. Theoretically, then, most cancers could be prevented if the factors that cause them can first be identified and then controlled or eliminated. Throughout their lives, people are exposed to many chemicals and some drugs in small amounts and in many combinations unique to their culture and environment. Many chemicals and drugs are now known to cause human cancer, and many more are suspected carcinogens. People who are exposed to these chemicals either directly, such as those who work in the particular industry shown, or indirectly, such as firefighters exposed to burning objects made from these chemicals, are at increased risk of developing the cancer listed in the table. The incidence of certain cancers in particular populations reflects prolonged low-level exposure to many carcinogens (chemical substances that cause cancer), cocarcinogens (substances that activate carcinogens), and promoting factors (substances that facilitate the action of carcinogens).
The mortality rate from lung cancer has been increasing since 1968, even though it has been known throughout that period that cigarette smoking is the major cause of the disease. It has been estimated that 30 percent of all cancers may be related to smoking, either directly or indirectly. The incidence of cancers of the lung, head and neck, esophagus, pancreas, kidney, and bladder is increased in people who smoke. The fifteen carcinogens that have been found in tobacco smoke include hydrocarbons and aromatic amines. People who work with asbestos or uranium or who drink alcohol have an increased risk and incidence of cancer if they also smoke. (This is called synergism, an action of two or more substances achieving a result of which each substance individually is incapable.) It seems reasonable then to explore ways to decrease the number of cancers related to smoking and other known human carcinogens by reducing the number of new smokers, encouraging current smokers to quit, and eliminating the other carcinogens altogether from our diet or eliminating our exposure to them.
Due to differences in their genetic make-up, individuals exposed to a carcinogen will not all have the same probability of getting cancer. Certain proteins from the liver, called enzymes, can break down or activate the carcinogen at different speeds in different people to either render it harmless or promote it to cause cancer. These enzymes will either destroy or activate carcinogens to varying degrees according to inherited tendencies. Some foods can induce certain enzymes to destroy certain carcinogens. The most potent food sources to induce these enzymes are vegetables of the Brassicaceae family, which includes Brussels sprouts, cabbage, and broccoli.
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Cancer
