If you're fishing for ways to reduce the risk of heart disease, you might start with the seafood-rich diet typically served up in Japan. According to new research, a lifetime of eating tuna, sardines, salmon and other fish appears to protect Japanese men against clogged arteries, despite other cardiovascular risk factors.
The research, published in the August 5, 2008, issue of Journal of the American College of Cardiology (JACC), suggests that the protection comes from omega-3 fatty acids found in abundance in oily fish. In the first international study of its kind, researchers found that compared to middle-aged white men or Japanese-American men living in the United States, Japanese men living in Japan had twice the blood levels of omega-3 fatty acids-a finding that was independently linked to low levels of atherosclerosis.
"The death rate from coronary heart disease in Japan has always been puzzlingly low," said Akira Sekikawa, M.D., Ph.D, an assistant professor of epidemiology at the University of Pittsburgh, PA, and an adjunct associate professor at Shiga University of Medical Science, Otsu, Japan. "Our study suggests that the very low rates of coronary heart disease among Japanese living in Japan may be due to their lifelong high consumption of fish."
Japanese people eat about 3 ounces of fish daily, on average, while typical Americans eat fish perhaps twice a week. Nutritional studies show that the intake of omega-3 fatty acids from fish averages 1.3 grams per day in Japan, as compared to 0.2 grams per day in the United States.
Earlier studies by Dr. Sekikawa's team showed that Japanese men had significantly less cholesterol build-up in their arteries when compared to white men living in the United States-despite similar blood cholesterol and blood pressure readings, similar rates of diabetes and much higher rates of cigarette smoking. It was unclear, however, whether Japanese men were protected by strong genes, a high-fish diet or some other factor.
To answer that question, the ERA JUMP (Electron-Beam Tomography, Risk Factor Assessment Among Japanese and U.S. Men in the Post-World War II Birth Cohort) Study enrolled 868 randomly selected men aged 40 to 49. Of these, 281 were Japanese men from Kusatsu, Shiga, Japan; 306 were white men from Allegheny County, Pennsylvania; and 281 were third- or fourth-generation Japanese-American men from Honolulu, Hawaii.
All study participants had a physical examination, completed a lifestyle questionnaire, and had standard blood tests to evaluate cardiovascular health. Laboratory tests also measured total blood levels of fatty acids and the omega-3 fatty acids that come from fish (specifically, eicosapentaenoic, docosahexaenoic and docosapentaenoic acids).
In addition, researchers used two techniques to measure the level of cholesterol build-up in the arteries. In the first test, ultrasound waves gauged the thickness of the walls of the carotid arteries in the neck, a test known as intimal-medial thickness (IMT). In the second test, an electron-beam CT scanner measured calcium deposits, or "hardened" cholesterol, in the arteries of the heart, a test known as coronary artery calcification (CAC). Both have been shown to identify people at high risk for heart disease.
Dr. Sekikawa and his colleagues found that the total level of fatty acids was similar in the three groups, but the percentage represented by fish-based omega-3 fatty acids was two-fold higher in Japanese men living in Japan (9.2 percent) when compared to white men (3.9 percent) and Japanese-American men (4.8 percent) living in the United States.
The researchers also found that levels of atherosclerosis were similar in Japanese-American and white men, but markedly lower in Japanese men living in Japan. The average IMT was 37 µm less in Japanese than white men after age and cardiovascular risk factors were taken into account, while the average risk-adjusted difference in the proportion of Japanese and white men with positive CAC tests was 11 percent. Both gaps were highly significant, but became statistically insignificant when differences in omega-3 fatty acid levels were taken into account.