The study findings, published in Heart, report that middle-aged Japanese men living in Japan had lower incidence of coronary artery calcification, a predictor of heart disease, than middle-aged white men living in the United States, likely due to the significantly higher consumption of omega-3 fatty acids found in fish.
Led by Dr Akira Sekikawa from the University of Pittsburgh, the study followed nearly 300 men for five years, tracking multiple factors that affect cardiovascular health, including cigarette smoking, the level of cholesterol in the blood and alcohol consumption, as well as their rates of diabetes and high blood pressure.
After accounting for risk factors for heart disease, the U.S. men had three times the incidence of coronary artery calcification as the Japanese men, said the team – while the levels of marine-derived omega-3 fatty acid in the blood were more than 100% higher in the Japanese than in the white men.
"The vast difference in heart disease and levels of marine-derived omega-3 fatty acid are not due to genetic factors," said Sekikawa. "When we look at Japanese Americans, we find that their levels of coronary artery calcification are actually higher than that of the rest of the U.S. population."
"Multiple studies have looked at the effect of fish oil on cardiovascular health, with mixed results," she added. "Previous studies investigated substantially lower intake of omega-3 fatty acids than what people in Japan actually get through their diet.”
“Our study seems to indicate that the level of marine-derived omega-3 fatty acids consumed must be higher than previously thought to impart substantial protection," said Sekikawa.
The team noted that the average dietary intake of fish by Japanese people living in Japan is nearly 100 grams each day, while the average American eats about 7 to 13 grams of fish a day, or about one serving a week.
Analysis of their data showed that Japanese men had a significantly lower incidence rate of coronary artery calcification (CAC) compared to white men.
“The incidence rate ratio of CAC taking follow-up time into account between Japanese and white men was 0.321. After adjusting for age, systolic blood pressure, low density lipoprotein cholesterol, diabetes, and other potential confounders, the ratio remained significant,” revealed Sekikawa and colleagues.
"Our findings indicate that it is worthwhile to take another look at the effect of marine-derived omega-3 fatty acids on heart disease, particularly when consumed at higher rates than previously investigated,” said Sekikawa.
Published online ahead of print, doi: 10.1136/heartjnl-2013-304421
“Long chain n-3 polyunsaturated fatty acids and incidence rate of coronary artery calcification in Japanese men in Japan and white men in the USA: population based prospective cohort study”
Authors: Akira Sekikawa, Katsuyuki Miura, et al