THE CAUSES AND PREVENTION OF CANCER - GAINING PERSPECTIVE

Epidemiological studies have identified several factors that are likel y to have a major effect on reducing rates of cancer: reduction of smo king, increased consumption of fruits and vegetables, and control of i nfections. Other factors include avoidance of intense sun exposure, in creased physical activity, and reduced consumption of alcohol and poss ibly red meat. Risks of many types of cancer can already be reduced, a nd the potential for further reductions is great. In the United States , cancer death rates for-all cancers combined are decreasing, if lung cancer (90% of which is due to smoking), is excluded from the analysis . We review the research on causes of cancer and show why much cancer is preventable. The idea that traces of synthetic chemicals, such as D DT, are major contributors to human cancer is not supported by the evi dence, yet public concern and resource allocation for reduction of che mical pollution are very high, in part because standard risk assessmen t uses linear extrapolation from limited data in high-dose animal canc er tests. These tests are done at the maximum tolerated dose (MTD) and are typically misinterpreted to mean that low doses of synthetic chem icals and industrial pollutants are relevant to human cancer. About ha lf the chemicals tested, whether synthetic or natural, are carcinogeni c to rodents at such high doses. Almost ail chemicals in the human die t are natural. For example, 99.99% of the pesticides we eat are natura lly present in plants to ward off insects and other predators. Half of the natural pesticides that have been tested at the MTD are rodent ca rcinogens. Cooking food produces large numbers of natural dietary chem icals. Roasted coffee, for example, contains more than 1000 chemicals: of 27 tested, 19 are rodent carcinogens. Increasing evidence supports the idea that the high frequency of positive results in rodent bioass ays is due to testing at the MTD, which frequently can cause chronic c ell killing and consequent cell replacement-a risk factor for cancer t hat can be limited to high doses. Because default risk assessments use linear extrapolation. which ignores effects of the high dose itself, low-dose risks are often exaggerated. - Environ Health Perspect 105(Su ppl 4):865-873 (1997).