[Epidemiological aspects of cancer and dietary habits]

Causal association between dietary habits and cancer is supported by both epidemiological and laboratory studies and dietary factor is at present one of the most important risks in carcinogenesis. However, the mechanisms of long low-dose exposure to dietary metabolites in carcinogenesis are little known, and there could be many other factors intervening over a long latent period, even if initiation and promotion of cancer occurred as a result of such dietary factors. The purpose of this paper was to review very preliminary reports on epidemiological studies carried out by Ogata-Segi among Japanese in Japan and by Haenszel among Japanese-Americans in Hawaii, together with those of others in the recent years and to evaluate the role of dietary factors in carcinogenesis. Recent epidemiological studies have repeatedly confirmed such dietary effects on cancers, but short-term intervention trials based on certain nutrients such as vitamins and minerals failed to demonstrate any suppressive effects among human populations. A number of other prospective studies on dietary intervention are in progress, but it appears to be difficult to obtain direct evidence from such studies on the population level, due to a lack of knowledge of the complicated metabolic processes of nutrients and their carcinogenic influence on cells and tissues.