Epidemiological aspects of fish in the diet.

Fish consumption is not a characteristic of the diet of every European culture. In the thirteen cohorts of the five European countries that participate in the Seven Countries Study the fish consumption varied between no fish in Velika Krsna (Serbia) and an average of about 95 g/d in Dalmatia (Croatia) (Kromhout et al. 1989). Even higher intakes were observed among fishermen in Japan (250 g/d) and Eskimos who consumed 400 g seafoodd. It has been shown that mortality from coronary heart disease is low among Eskimos and Japanese. Also the Dalmatian cohort of the Seven Countries Study is characterized by a low mortality rate from coronary heart disease (Menotti et al. 1993). It is attractive, therefore, to suggest that fish consumption may lower the risk for coronary heart disease. Population comparisons in relation to diet-disease associations may be confounded by other dietary factors. The diets of the Eskimos, Japanese and Dalmatians are not only characterized by a high fish consumption but also by a relatively low intake of saturated fat. It may be hypothesized, therefore, that the low mortality rates for coronary heart disease can alternatively be explained by a low intake of saturated fat. Consequently prospective studies are needed to investigate the association between fish consumption and coronary heart disease mortality on the individual level. In 1985 we published a paper showing an inverse relationship between fish consumption and 20-year mortality from coronary heart disease in the Zutphen Study, the Dutch contribution to the Seven Countries Study (Kromhout et al. 1985). This association was independent of other coronary heart disease risk factors. This inverse association was confirmed by the results of three other cohort studies: two from the USA, the Western Electric and the MRFIT study and by the Swedish Twin Study (Shekelle et al. 1985; Norell et al. 1986; Dolecek & Grandits, 1991). Also in a case-control study carried out among Italian women an inverse relationship was found between fish consumption and myocardial infarction (Gramenzi et al. 1990). All those populations were characterized by a relatively low fish consumption, e.g. less than 50 g fish/d. In prospective studies carried out in cultures with a relatively high fish consumption pattern, e.g. coastal Norway and Hawaii no such association was found. This is possibly due to the fact that in these cultures a proper reference group, e.g. persons who did not consume fish, is lacking. These results from observational studies are supported by the results of a secondary intervention trial carried out in Wales (Burr et al. 1989). A group of 2000 patients with a myocardial infarction were randomized into an experimental group and a control group. The patients in the experimental group got the advice to eat fatty fish at least three times weekly. Their fish consumption was four times as high as in the control group. After 2 years of follow-up a significantly lower mortality from coronary heart disease and from all causes was observed in the experimental group compared with the control group. Also these results support the hypothesis that a small amount of fish may protect against coronary heart disease.