Epidemiologic studies of vitamins and cancer of the lung, esophagus, and cervix.

Epidemiologic studies of the relationships between vitamins and 3 types of cancer are reviewed. First, the widely reported association between vitamin A and beta-carotene and risk of lung cancer is considered. In a large population-based case-control study of lung cancer among white males in New Jersey, increased intake of vegetables, dark green vegetables, dark yellow-orange vegetables, and carotenoids were each associated with reduced risk, but intake of retinol or total vitamin A was not related. The protective effect of vegetables was limited to current and recent cigarette smokers, which suggests that vegetable intake prevents a late-stage event in carcinogenesis. Consumption of dark yellow-orange vegetables was consistently more predictive of reduced risk than either the total carotenoid index or consumption of any other food group, possible because of the high content of beta-carotene in this food group. The results and limitations of other epidemiologic studies of diet and lung cancer are reviewed. Second, the evolving relationship between multiple micronutrient deficiencies and esophageal cancer is discussed. In a death certificate-based case-control study of esophageal cancer in black males in Washington, D.C., several indicators of general nutritional status, including consumption of fresh or frozen meat and fish, dairy products and eggs, and fruit and vegetables, and the number of meals eaten per day, were inversely and independently correlated with the risk of esophageal cancer. Estimates of intake of micronutrients, such as carotenoids, vitamin C, thiamin, and riboflavin, were less strongly associated with reduced risk than were the broad food groups that provide most of each micronutrient. Thus no single micronutrient deficiency was identified. Other studies suggest that generally poor nutrition may partially explain the susceptibility of urban black men to esophageal cancer. Finally, the postulated association between low folacin levels and risk of cervical cancer is examined. Among women who use oral contraceptives, serum and red blood cell folacin levels were reported to be lower among those with cervical dysplasia. In a clinical trial involving oral contraceptive users, cervical dysplasia gradually decreased in the group supplemented with oral folate but remained unchanged in the group given the placebo. Other epidemiologic studies of diet and cervical cancer are discussed.