According to this study, Hisayama Study is an ongoing, population-based epidemiologic study in the town of Hisayama, which is in a suburb of the Fukuoka metropolitan area on Kyushu Island, Japan. Whether the intake of eicosapentaenoic acid (EPA) or arachidonic acid (AA) affects the risk of cancer remains unclear, and the association between the serum EPA:AA ratio and cancer risk has not been fully evaluated in general populations.

Omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), must be obtained from foods because the amounts synthesized in the human body are very small. The main dietary sources of omega-3 PUFAs are marine fish and fish oil.

Omega-3 PUFAs constitute an important component of human cell membranes and regulate inflammatory responses through the production of lipid mediators termed eicosanoids. Growing epidemiologic evidence suggests that the consumption of fish, fish oil, and omega-3 PUFAs protects against the development of cardiovascular diseases, inflammatory diseases and mental illnesses.

The population of Hisayama is approximately 8400 and has been stable for 50 years, and the age and occupational distributions of the town population are almost identical to those of Japan. The rationale, study design, and methods of the Hisayama Study have been described elsewhere.

Our prospective study of a general Japanese population suggests that lower levels of the serum EPA:AA ratio are associated with an increased risk of cancer death. This association remained robust even after adjustment for other confounding risk factors. In particular, the risk of death from liver cancer significantly increased with lower levels of the serum EPA:AA ratio.

By contrast, we found no clear evidence of an association between the serum DHA: AA ratio and cancer death. To the best of our knowledge, this is the first report to show that decreased serum EPA: AA levels are an independent risk factor for cancer death. These findings suggest that the regular intake of EPA-rich foods may be effective for reducing the risk of cancer in the general Japanese population.

In conclusion, the present analysis showed that lower levels of the serum EPA: AA ratio, but not the serum DHA: AA ratio, were significantly associated with a greater risk of cancer death. These associations suggest that lower serum EPA: AA ratios are a possible risk factor for cancer death. Notably, the serum EPA: AA ratio may relate to the risk of death from liver cancer.

These findings imply that the regular intake of EPA-rich foods may be effective for reducing the risk of cancer. Further large-scale prospective cohort studies will be needed to confirm the influence of the serum EPA: AA ratio on the risk of cancer death.