Japanese fish diet ‘key to healthy heart’

According to the researchers, the protection actually comes from Omega-3 fatty acids found in plenty in oily fish, the Journal of the American College of Cardiology reported.

“The death rate from coronary heart disease in Japan has always been puzzlingly low. 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,” said Akira Sekikawa of University of Pittsburgh.

For their study, the researchers enrolled 868 randomly selected men aged 40 to 49. Of these, 281 were Japanese from Kusatsu in Japan; 306 were whites from Pennsylvania; and 281 were third- or fourth-generation Jap-American men from 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.

In addition, the 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 per cent) when compared to white men (3.9 per cent) and Jap-American men (4.8 per cent) 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 ‘b5m 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 per cent.

Both gaps were highly significant, but became statistically insignificant when differences in Omega-3 fatty acid levels were taken into account, the study found.

“Our study clearly demonstrated that whites and Japanese-Americans have similar levels of atherosclerosis, which are much higher than in the Japanese in Japan. This indicates that much lower death rates from coronary heart disease in the Japanese in Japan is very unlikely due to genetic factors,” Dr Sekikawa said.