Diet and Cancer: Epidemiological Approaches

Dietary habits are the most important factor in both development and prevention of carcinogenesis. Geographical differences in cancer incidences are mostly attributable to country-specific lifestyles. In Japan, time trends of cancer mortality rates have shown decreasing stomach and uterine cancer rates, and increasing incidences of lung, colon, and breast cancer. These changes may have been caused by changes in the Japanese lifestyle after World War II. Cancer incidences in hormone-related organs, such as of the breast, ovaries, and prostate in Japan are lower than those in Caucasians. The intake of soybeans is considered preventive for these cancers. This protective effect is postulated to be due to the activity of phytoestrogens such as daidzein and genistein. The composition of bacterial flora is thought to play an important role in the absorption and metabolism of phytoestrogens. Geographically, Japan is a long country from north to south in which cancer incidence shows considerable variation. We are conducting a population-based prospective study in 11 health center districts (Koseisho Multipurpose Cohort) to understand the relationship between dietary, lifestyle, and other environmental factors and the occurrence of chronic diseases. The study design has already been introduced. Various constituents of foods are discussed in relation to cancer development and prevention. The usefulness of biomarkers in prospective studies is also discussed.