Case-control studies on vitamins and cancer in a multiethnic population

Attempts to explain the remarkable differences in cancer rates among ethnic groups in Hawaii have centered on studies of environmental exposures, especially the diet. Risk factors, such as dietary fat, and possible protective factors, such as vitamins, have been investigated extensively. Case-control studies that examined vitamin intake have been completed for several cancer sites, including the lung, prostate, bladder, and thyroid. Cancers currently under study, for which only preliminary data are available, include colorectal cancer, endometrial cancer, and malignant melanoma. Although the findings vary by cancer site, the results of the completed studies suggest that beta-carotene, other carotenoids, or vitamin C may be protective against lung and bladder cancer. However, because other constituents with potential anticancer properties are present in the fruits and vegetables that are the primary sources of these nutrients, the data have also been examined for the effects of specific foods and food groups. These analyses suggest that there may be interactions among various food constituents in their effects on cancer risk. Data from the study of lung cancer were used to illustrate the potential impact of changes in food or nutrient-consumption levels on cancer incidence. Based on calculations of the attributable risk due to low intake of beta-carotene or vegetables as a group, it appeared that the incidence of lung cancer in our population could be lowered by 20% to 40% on the basis of diet, independent of changes in smoking behavior. These results support the value of public health measures that encourage greater intakes of vitamin A, vitamin C, and other substances with cancer-inhibiting properties.