Dietary history methods for epidemiologic studies: application in a case-control study of vitamin A and lung cancer

A dietary history method for use in a case-control study of vitamin A and lung cancer is described. The method was designed to obtain estimates of the usual frequencies and quantities of 84 major food sources of vitamin A and carotene consumed prior to symptoms of disease in cases and during the same time period in matched controls. Amounts were estimated from photographs of each item that showed three different quantities. The development of the questionnaire is described in detail, as well as the data collection and analysis. The results of the study showed that relative to those men with the highest intakes, the men who consumed less vitamin A or carotene had a higher risk for lung cancer in a general dose-response fashion. These findings were not apparent for females. Recommendations regarding dietary methodology for future studies concerning vitamin A and carotene intakes include further research on the validation and reproducibility of the dietary methods, identification of appropriate biological markers that reflect past exposures of vitamin A and carotene, and further research on the vitamin A and carotene content of available food items.