[Fish, n-3 polyunsaturated fatty acid and colorectal cancer prevention: a review of experimental and epidemiological studies].

Colorectal cancer demonstrates high incidences in the developed countries and is the second largest cause of deaths from neoplasia. In Japan, about 12% of all cancer deaths are due to colorectal cancer and the rate continues to increase remarkably. Dietary factors are clearly linked to the development of tumors in the colorectum, and the increase in mortality from colorectal cancer over the last few decades in Japan has been attributed to Westernization of the diet. On the other hand, the intake of fish/n-3 polyunsaturated fatty acids has long been considered as a factor decreasing the risk of colorectal cancer. In the present study, we investigated the effect of fish/n-3 polyunsaturated fatty acids on colorectal cancer by reviewing papers on both experimental and epidemiological studies overall to obtain a perspective for research and practice for prevention. This review covers the following areas. 1. Relationships between n-3 polyunsaturated fatty acids and colon carcinogenesis in experimental studies. 1) Aberrant crypt foci (ACF). 2) Tumors. 2. Relationships between fish intake and colorectal cancer in epidemiological studies. 1) Ecological studies. 2) Case-control studies. 3) Cohort studies. 4) Randomized controlled trials. There are substantial data from experimental studies in support of anticarcinogenic effects of fish/ n-3 polyunsaturated fatty acids in the colon. Several epidemiological studies have also provided evidence that fish/n-3 polyunsaturated fatty acids have anticarcinogenic effects in the colon, but not all data are consistent. However, increasing intake of fish/n-3 polyunsaturated fatty acids for preventing colon cancer is suggested from review of experimental and epidemiological research overall. In the future, it is necessary to improve precision regarding exposure to carcinogens and fish/n-3 polyunsaturated fatty acids intake using a detoiled dietary survey and biomarkers in epidemiological studies.