Japanese men eat about 10 times more fish than Caucasian American men. That dietary fact could help explain why middle-aged Japanese men have less than a third the rate of coronary artery calcification than their American counterparts.
An international study involving the University of Pittsburgh Graduate School of Public Health has found that fish consumption may have advantages in heart health. But the level of marine-derived omega-3 acids consumed must be higher than previously thought to impact substantial protection, said Akira Sekikawa, a Pitt associate professor of epidemiology and the study's lead author.
Omega-3 fatty acids used in earlier studies may have involved a "substantially lower intake of omega-3 fatty acids than what people in Japan actually get through their diet," he said.
The five-year study, published online in the journal Heart, was funded by the National Institutes of Health and included scientists from Japan, Hawaii and Philadelphia.
It included 175 middle-aged Japanese men and 113 middle-aged Caucasian Americans. Japanese-American men in the study were found to have levels of coronary artery calcification -- the accumulation of calcified plaques in coronary arteries -- proved to be as high or even higher than Caucasian American men, revealing the lower rate of the calcification among Japanese men is not genetically based.
Such calcification is a strong biomarker for a heightened risk of heart disease. Multiple studies have looked at the effect of fish-oil consumption, rather than fish consumption, on cardiovascular health, with mixed results.
After researchers adjusted for various risk factors for heart disease, including cholesterol, blood pressure, smoking, and alcohol use, the results showed that larger quantities of fish oil that Japanese men consume seem "to impart a protective factor that wards off heart disease," Dr. Sekikawa said.
But a larger clinical trial would be necessary to confirm those results.
For that reason, he said, he cannot yet encourage Americans to consume as large a quantity of fish as the Japanese do. The study didn't evaluate the benefits or risks of fish-oil supplements, which also have shown mixed results in various studies.
Two key omega-3 fatty acids -- docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) -- are found in fatty fish such as salmon, mackerel, sardines and herring. Another omega-3 acid that can be converted into DHA and EPA is found in plant-based fats such as flaxseed oil.
The American Heart Association recommends at least two servings of fish a week but states that fish can contain "high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other environmental contaminants."
Other studies of men taking fish-oil supplements have produced contradictory results on whether fish oil is beneficial or detrimental to prostate health. While Japanese men, and Asian men in general, have low rates of prostate cancer, many dietary and health factors could be responsible.
"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," Dr. Sekikawa said.
David Templeton: firstname.lastname@example.org or 412-263-1578.