(07-04-06) Frequent Fish Consumption Prevents Heart Disease in Japanese

Cardiovascular disease claims more lives in western countries than any other cause. In Asia, where fish consumption is up to 10 times greater than in America and most of Europe, mortality from ischemic heart disease is a fifth of that in Finland, Hungary and the Czech Republic (46 vs 230 deaths/100,000 men). The proportion is similar for women, though the rates are about half those in men. While there are many other diet and lifestyle differences between these countries, the pronounced effect of the omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) in fish on reducing the risk of cardiovascular mortality?50% or more?makes this factor particularly interesting.

Regular consumption of fish is associated with lower mortality from all causes in some studies, but is most pronounced for sudden coronary death, all cardiovascular diseases, and stroke. Most studies in western countries have reported no effect on nonfatal coronary events, but risk of having a first heart attack is significantly lower among fatty fish eaters. Increased consumption of n-3 LC-PUFAs at a level of about 1 gm/day prolongs life in those who have already survived a heart attack. Less is known about the amounts of n-3 LC-PUFAs or fish that might confer protection in those with very high fish consumption. In other words, does the cardiovascular benefit in the early stages of the disease, and if so, at what level of intake?

No population is better suited to answer this question than the Japanese, who eat fish at least once a week, averaging about 100 gm of fish/day, or nearly 10 times the US consumption of about 12 gm/day. Iso and colleagues at the University of Tsukuba, Japan, followed a cohort of 41,578 Japanese men and women, aged 40 to 59 years, from 1990-92 until 2001, documenting fish intake at baseline and fish intake and causes of death 5 years later. They examined the relationship between quintiles of fish intake and incident heart disease (new cases), probable and confirmed myocardial infarctions, and sudden cardiac deaths. Hazard ratios were calculated after adjustment for age, sex, and potential confounding variables.

Fish intake varied from an average of 23 gm/day in the lowest quintile to 180 gm/day in the highest group, and accounted for an average n-3 LC-PUFA intake ranging from 0.3 to 2.1 gm/day. Over the 10-year follow-up period there were 258 incident cases of coronary heart disease, of which 62 were fatal and 196 nonfatal. Of the 62 deaths, 37 were attributable to sudden cardiac death.


Fish consumption and calculated n-3 LC-PUFA intake were significantly and inversely associated with age and sex-adjusted risk of total coronary heart disease, myocardial infarction, and nonfatal coronary events. When adjustments were made for additional variables, such as cigarette smoking and alcohol consumption, the associations remained significant for myocardial infarction and nonfatal coronary events. In those consuming fish 8 times/week (Q5, Figure 1), risk of coronary heart disease was approximately 40% lower than in those eating fish once/week (Q1). In the highest fish-eating group, risk of nonfatal coronary events was nearly 60% lower and risk of myocardial infarction 50% less than in the lowest fish-eating group. However fish consumption was not associated with risk of sudden death or other coronary fatalities. Strong inverse associations for risk of myocardial infarction and nonfatal coronary events were also observed for consumption of n-3 LC-PUFAs.

This prospective observational study deserves attention for several reasons. It clearly implies the primary prevention of coronary heart disease with fish or n-3 LC-PUFA intake. In a large, free-living population without cardiovascular disease at enrolment, consumption of ?large? amounts of fish was associated with enhanced prevention of coronary heart disease, myocardial infarction, and nonfatal coronary events. When the analysis controlled for several other confounding variables, risk reduction for myocardial infarction and all nonfatal coronary events remained statistically significant. The incidence of coronary heart disease in the lowest and highest fish consumption groups ranged from 0.9% to 0.5%, respectively, calculated from uncorrected data. As little as 23 grams of fish/day, equivalent to 300 mg EPA + DHA, was associated with an incidence of heart disease of about 1%. For perspective, the prevalence (existing cases) of coronary heart disease in the U.S. for white men and women is 8.9% and 5.4%, respectively. Incident myocardial infarction and nonfatal coronary events were likewise extremely low in this large sample of Japanese adults.

The more frequently people ate fish, the greater the cardiovascular benefits. For myocardial infarction and nonfatal coronary events, higher fish intake was associated with significantly reduced chance of developing these conditions in a multivariate analysis. Those in the highest quintile of intake had a nearly 60% lower chance of nonfatal coronary events than those in the lowest quintile. With few exceptions, previous epidemiological studies, mostly in western populations, reported no significant effect of fish consumption on nonfatal coronary events and myocardial infarction. The contrast between those consuming western diets and the present study suggests a threshold effect of fish or n-3 LC-PUFA intake for meaningful reduction in coronary disease risk. In this study, a threshold above 300 mg n-3 LC-PUFAs/day was indicated.

Unlike previous reports in western populations, fish and n-3 LC-PUFA intake were not associated with reduced risk of sudden cardiac death or fatal coronary events. This finding was in all probability related to the very low occurrence of cardiac fatalities in the study. If there is a threshold for the prevention of sudden cardiac deaths, this population was above it. Other data among Japanese have reported similar findings.

This study adds to the evidence that consuming fish frequently lowers the risk of cardiovascular disease. Those consuming low-fish western diets might not only reduce their chance of dying from coronary heart disease, but avoid the condition in the first place by consuming fish or n-3 LC-PUFAs much more often. Too few deaths from heart disease to permit statistical analysis is telling evidence that eating fish frequently protects heart health. The Japanese are definitely on to something fishy.

Iso H, Kobayashi M, Ishihara J, Sasaki S, Okada K, Kokubo Y, Tsugane S: JPHC Study Group. Intake of fish and n3 fatty acids and risk of coronary heart disease among Japanese: the Japan Public Health Center-Based (JPHC) Study Cohort I. Circulation

Source: the pufa newsletter

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