Health Focus Archive
The Cancer Prevention Lifestyle
While the process involved in the development of cancer is only partially understood, it is known that cancer develops through contact with one or more carcinogens that cause the genetic changes that allow cells to grow out of control.
It is believed that there are two types of carcinogens involved in causing most cancers. Initiators start the cellular damage that can lead to cancer, and promoters allow genetically damaged cells to proliferate at a greater rate than the normal cells. For example, alcohol promotes cancer of the mouth and oesophagus when combined with an initiator such as tobacco.
Scientists at the National Cancer Institute estimate that about 80% of all cancer cases are related to life-style. The good news is that some life-style factors actually prevent the development of cancer. Many cancers are preventable by avoiding carcinogens and following recommendations for a cancer-prevention life-style.
Former U.S. Surgeon General C. Everett Koop called tobacco use America's single most preventable cause of death. Tobacco use contributes to the three leading causes of death in North America: artery disease, cancer, and stroke.
Cigarette smoking causes 30% of all cancer deaths. About 90% of lung cancer patients are smokers. Cigarette smoking also causes cancers of the larynx, oesophagus, pancreas, bladder, kidney, and mouth. Low-tar and low nicotine cigarettes are no solution, because they actually increase the smoker's risk of cancers of the mouth and throat. Pipe smoking increases the smoker's risk of cancers of the mouth, tongue, and throat, and chewing tobacco increases the user's risk of cancer of the mouth.
Tobacco smoke contains hundreds of damaging chemicals, and includes both cancer initiators and promoters. For example, the phenols found in tobacco tar greatly increase the carcinogenic potency of benzopyrene, another substance found in cigarette tar. (Cigarette tar refers collectively to several hundred different chemicals in cigarettes that, when condensed, form a brown, sticky substance.)
Heavy alcohol use (more than two drinks a day) is associated with cancers of the mouth, throat, oesophagus, and liver. (One drink contains about 0.6 oz of alcohol, and is comparable to 1.5 oz of liquor, a 5-oz glass of wine, or a 12oz glass of beer.) People who drink and smoke have a much greater risk of getting cancers of the mouth and oesophagus. Alcohol may also contribute to the development of breast cancer.
Viruses may act as carcinogens. Many of the viruses associated with an increased risk of cancer [such as human papilloma virus (HPV)] are spread through sexual contact. Sexually active people should follow safer-sex practices, such as using condoms during sexual contact, to reduce the likelihood of getting these viruses.
Several dietary factors are associated with a person's risk of developing cancer. Carcinogens are found in foods that are smoked, cured, and pickled.
Consumption of pesticide residues on fruits and vegetables and in meats may increase an individual's cancer risk.
Fat intake may be the major and most controllable dietary carcinogen in North America. Fat appears to act as a cancer promoter, especially in cancers of the breast and colon. These are the leading causes of cancer deaths in non-smoking North Americans.
Some dietary chemicals may block cancer promotion: retinoids, vitamins C and E, and the mineral selenium. Researchers have theorised that some carcinogens cause cancer by producing highly reactive oxygen atoms called free radicals, which may cause damage to cell components, such as DNA. Retinoids, vitamins C and E, and selenium appear to act as antioxidants; that is, they neutralise these reactive chemicals and thus block their carcinogenic effect.
Retinoids can be converted to vitamin A in the body. While too much vitamin A is toxic, retinoids in quantity appear to be safe. Good sources of retinoids include dark green vegetables such as spinach and broccoli, and yellow fruits and vegetables such as cantaloupe, apricots, carrots, and yams.
Vitamin C is found in many fruits and vegetables such as citrus fruits, strawberries, and potatoes. Vitamin E, a normal component of cell membranes, is found in vegetable oils, and selenium is found in seafood, whole grains, and organ meats.
Studies on both humans and animals suggest that fiber may help prevent cancers of the colon and rectum. Fiber is plant material that people can't digest. These materials may be divided into two categories: water soluble and water insoluble. It is the insoluble type, which comes from the structural components of plants, that is linked with a healthy digestive tract. Insoluble fiber is found in whole-grain cereals, wheat bran, breads, and many vegetables.
A family of plants known as cruciferous vegetables also contains antioxidants and has received some attention as possible cancer preventers. These vegetables include broccoli, brussels sprouts, cabbage, and cauliflower.
Weight Control and Physical Activity
Life-insurance data indicate that people who are more than 20% above their recommended weight have a
higher than average risk of many types of cancer. Cancer risk increases with the amount of extra weight.
Several studies have found an association between low levels of occupational and/or recreational physical
activity and risk of colon cancer. Sedentary participants in one study had two to three times the risk of colon
cancer as more active participants. The intensity of the activity does not appear
to be an important variable. People
who performed even mild physical
activity, such as walking, had a lower
cancer risk than sedentary folks.
Preliminary evidence also suggests that
active women may have fewer cancers
of the breast and reproductive system.
Carcinogens are present in many industrial and household products. Regulatory agencies, industries, and organised labour have developed procedures for reducing hazardous exposure to carcinogens in the workplace.
Household and garden products
should always be used as directed to
reduce exposure to fumes and contact
Ultraviolet light is a potent carcinogen, especially for light-skinned people.
Protective clothing and sunscreens can
prevent much of the carcinogenic effect
Personality and Stress
Some studies have found that cancer is more common among people who keep their anger and other emotions bottled up and who cope poorly with internal turmoil and stress. The association between stress and disease will be explored in next weeks health topic, Mind and Immunity.