IBARAKI-KEN, JAPAN. It is generally accepted that a moderate intake of fish, around two servings a week, reduces the risk of heart disease. But would a higher intake reduce the risk further? This question was investigated by researchers at the University of Tsukuba in Japan, a country in which 95 per cent of adults eat fish at least once a week, with an average fish intake of about 100 grams a day. The researchers gathered data on 19,985 Japanese men and 21,593 Japanese women aged 40 to 59 years. Participants were given a food frequency questionnaire and monitored for ten years. During this time (477,325 person-years of follow-up), there were 258 cases of coronary heart disease. After taking into account cardiovascular risk factors, exercise and certain dietary factors, those in the highest fifth for fish intake (180 g/d) were at a 56 per cent lower risk of heart attack compared with those in the lowest fifth (23 g/d). However the risk for sudden cardiac death was not reduced. In terms of fatality, the risk of a nonfatal coronary event was lowered (by 57 per cent) but the risk of a fatal coronary event was not lowered (although the small number of cases reduced statistical reliability).
The authors state that, compared with a modest fish intake of once a week or about 20 g/d, a higher intake is linked to a substantially reduced risk of coronary heart disease, primarily heart attack or nonfatal cardiac events, among middle-aged persons. They add that the lowest fifth of fish intake in this study corresponds to the middle fifth in Western studies. They conclude that a high fish intake can further reduce the risk of initial coronary heart disease events. The team also measured intake of n-3 polyunsaturated fatty acids (present in fish and certain other foods) and found a strong association with lower risk of heart attack (reduced by 65 per cent) and nonfatal coronary events (reduced by 67 per cent). They suggest several possible underlying mechanisms, such as a reduction in platelet aggregation and increased levels of vasodilators, which cause blood vessels to dilate. Furthermore, n-3 polyunsaturated fatty acids may reduce the number of inflammatory cells and help prevent atherosclerosis - hardening of the arteries. They may also reduce insulin resistance, blood fats, blood-clotting cells and blood pressure.
Iso, H. et al. 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, Vol. 113, January 17, 2006, pp. 195-202