Time-related factors in research on diet and cancer

Time-related factors have been an integral aspect of laboratory and epidemiologic studies concerning the effects of diet on cancer. In this survey, we illustrate several ways in which consideration of time factors has furthered our understanding in this area. As one of the key dimensions in descriptive studies of secular trends and migrant populations, time factors suggest general associations between diet and cancer. The investigation of time-related parameters such as age, duration of dietary exposure, and time from exposure to cancer, lends greater specificity to the diet-cancer relationship. Both micro- and macro-nutrients are examined, as well as nutrition-mediated factors such as growth and anthropometry. Time-related issues relevant to the design of future observational and intervention studies of diet and cancer (i.e. critical etiologic periods, timing of dietary assessment, biological indicators, and secular trends) are also discussed.