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.
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.
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.
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.
The importance of the fish-derived omega-3 fatty acids in reducing risk for heart disease is powerfully underscored by this cross-cultural study, said William S. Harris, Ph.D., senior scientist and director of the Metabolism and Nutrition Research Center, Sanford Research/University of South Dakota, Sioux Falls. “Japanese men in Japan have equally bad or worse cardiovascular risk profiles as Americans, but less heart disease? How can this be?” said Dr. Harris, who was not involved in the ERA JUMP study. “What really distinguishes the Japanese men from the Americans is the fact that blood levels of the omega-3 fatty acids are twice as high in Japan as they are in the West.