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Eating Fish May Explain Very Low Levels of Heart Disease in Japan

Consuming large quantities of fish loaded with omega-3 fatty acids may explain low levels of heart disease in Japan, according to a study led by the University of Pittsburgh Graduate School of Public Health slated for the Aug. 5 issue of the Journal of the American College of Cardiology and available online at 5 p.m. ET, today. The study also found that third- and fourth-generation Japanese Americans had similar or even higher levels of atherosclerosis, or hardening of the arteries – a major risk factor for heart disease, compared to white Americans.

The very low rate of heart disease in Japan among developed countries has been puzzling. Death rates from coronary heart disease in Japan have been less than half of that in the U.S. This holds true even among Japanese men born after World War II who adopted a Western lifestyle since childhood, and despite the fact that among these same men, risk factors for coronary heart disease (serum levels of total cholesterol, blood pressure and rates of type 2 diabetes) are very similar among men in the U.S. Additionally, the rate of cigarette smoking, another major risk factor, has been infamously high in Japan.

The study was conducted at two universities and one research institute in the U.S. and Japan to compare serum levels of omega-3 fatty acids and atherosclerosis among Japanese, white American and Japanese American men. Based on data from 868 men between the ages of 40 and 49, Japanese men had the lowest levels of atherosclerosis and two times higher levels of omega-3 fatty acids than white Americans or Japanese Americans.

The differences in the levels of atherosclerosis between Japanese and white Americans remained after adjusting for other risk factors – serum cholesterol, blood pressure, cigarette smoking, body mass index and diabetes.

"Our study suggests that very high levels of omega-3 fatty acids have strong properties that may help prevent the buildup of cholesterol in the arteries," said Akira Sekikawa, M.D., Ph.D., study lead author and assistant professor of epidemiology at the University of Pittsburgh Graduate School of Public Health. "Increasing fish intake to two times a week for healthy people is currently recommended in the U.S. Our study shows much higher intake of fish observed in the Japanese may have strong anti-atherogenic effect."

Fish consumption among the Japanese is one of the highest in the world. Japanese men consume an average of 100 grams, equivalent to about 3.75 ounces, of fish every day from early in life. Meanwhile, Americans typically eat fish less than two times a week.

"The Japanese eat a very high level of fish compared to other developed countries," said Dr. Sekikawa. "While we don't recommend Americans change their diets to eat fish at these quantities because of concerns about mercury levels in some fish, increasing intake of omega-3 fatty acids in the U.S. could have a very substantial impact on heart disease. Given the similar levels of atherosclerosis in Japanese Americans and white Americans, it also tells us that lower levels of heart disease among Japanese men are much more likely lifestyle related than a result of genetic differences," said Dr. Sekikawa.

Omega-3 fatty acids are a type of polyunsaturated fat found primarily in fish. The two most potent omega-3 fatty acids are known as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) and are usually found in oily fishes, such as mackerel, salmon and tuna.