Résumé
Dietary factors are thought to be closely associated with the development of human cancers and hence numerous studies in this area have already been conducted in the United States and other Western countries. Comparatively few prospective studies have been published in Japan, especially for Hokkaido people. The present investigation was therefore performed to assess links between four leading cancers and some of the Japanese common dietary factors through a cohort study (1984-2002) in Hokkaido by analyzing 1,524 men and 1,634 women separately aged 40 and over. Adjusted Cox proportional hazard regression was used to calculate the relative risk (RR) for each dietary factor. For men, two dietary factors, miso soup (RR=0.2, 95% confidence interval (95%CI)=0.1-0.8) and pickled vegetables (RR=0.2, 95%CI=0.1-0.8) were associated with lower risk for stomach and colorectal cancer respectively. For women, three factors, namely salty confectionary (RR=3.5, 95%CI=1.1-10.9), black tea (RR=3.8, 95%CI=1.1-13.6), and carbonated drink/juice (RR=3.9, 95% CI=1.4-11.1) appeared related to an elevated risk of stomach cancer. However, further analysis simultaneously with all other adjusted factors indicated only carbonated drink/juice (RR=3.1, 95%CI=1.1-8.9) to present a significant risk factor for stomach cancer. One factor, namely wild edible plants (RR=3.3, 95%CI=1.1-9.8), increased the risk for colorectal cancer in women. None of the dietary components were significantly associated with lung or pancreatic cancers. This study also indicated a wide variation in the impact of dietary factors by sex and cancer site, in line with earlier work, pointing to a necessity for careful interpretation. Further epidemiological investigations by sex with more study subjects and confounding factors will be useful for determining the contribution of individual dietary factors to development of human cancers in Hokkaido, Japan.