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Etiology

Increasing fish intake did not reduce the risk for coronary disease in men

ACP J Club. 1995 Nov-Dec;123:79. doi:10.7326/ACPJC-1995-123-3-079


Source Citation

Ascherio A, Rimm EB, Stampfer MJ, Giovannucci EL, Willett WC. Dietary intake of marine n-3 fatty acids, fish intake, and the risk of coronary disease among men. N Engl J Med. 1995 Apr 13;332:977-82.


Abstract

Objective

To determine whether an association exists between a diet containing n-3 fatty acids from fish and the risk for coronary heart disease.

Design

6-year cohort analytic study of men participating in the Health Professionals Follow-up Study.

Setting

Population-based study in the United States.

Participants

44 895 male health professionals (age range 40 to 75 y in 1986) who were not diagnosed with cardiovascular disease and who had a daily caloric intake between 800 and 4200 kcal.

Assessment of risk factors

A questionnaire at baseline included items about the average frequency of consumption of specified portions of 131 foods (including 4 fish groups) during the previous year. 2 years later, a questionnaire was used to assess consumption of fish-oil supplements.

Main outcome measures

Fatal coronary disease (including sudden death), nonfatal myocardial infarction (MI), coronary artery bypass grafting, and angioplasty confirmed by a blinded review of the medical record, autopsy record, or death certificate.

Main results

1543 coronary events occurred during 242 029 person-years of follow-up: 264 deaths from coronary disease, 547 nonfatal MIs, and 732 coronary artery bypass or angioplasty procedures. After controlling for age; body mass index; smoking habit; alcohol consumption; profession; family history of MI before 60 years of age; and history of hypertension, diabetes, and hypercholesterolemia, no statistically significant association was seen between dietary intake of n-3 fatty acids or fish intake and the risk for coronary heart disease. The multivariate relative risk (RR) for coronary heart disease was 1.12 (95% CI 0.96 to 1.31) among men in the top fifth in terms of intake of n-3 fatty acids (median, 0.58 g/d) compared with men in the bottom fifth (median, 0.07 g/d). Among men who consumed ≥ 6 servings of fish per week, the multivariate RR for coronary disease was 1.14 (CI 0.86 to 1.51) compared with men who consumed ≤ 1 serving per month. The risk for coronary disease among men who ate any amount of fish was 0.74 (CI 0.44 to 1.23) compared with those who ate no fish.

Conclusion

Increasing dietary intake of fish or n-3 fatty acids from fish did not reduce the risk for coronary heart disease in men.

Source of funding: National Institutes of Health.

For article reprint: Dr. A. Ascherio, Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA. FAX 617-432- 2435.


Commentary

Fruit and vegetable intake reduced the risk for stroke in middle-aged men

The well-written reports by Gillman and Ascherio and their colleagues show that the Framingham Study, which was started in 1948, and the Health Professionals' Follow-up Study, which was started in 1986, continue to produce important results.

The study by Gillman and colleagues on fruits and vegetables and strokes supplements our mother's advice: It may take more than 1 apple a day to keep the doctor away! The authors note that, for each increment of increased intake of fruits and vegetables, a corresponding decrease occurred in the risk for cerebrovascular events.

The measurement of "exposure"—fruit and vegetable consumption at baseline—was based on a single 24-hour recall, which may be an imperfect reflection of a person's usual diet. An in-depth dietary assessment, such as multiple 24-hour food recalls, food records, or food frequency questionnaires, would have provided more meaningful information at both a macro- and micro-nutrient level and would have increased our confidence in ascribing the proposed benefit to the exposure.

The investigators considered all known confounders and, even after adjusting for smoking, the protective effect of fruit and vegetables on stroke incidence remained statistically significant. As in all observational studies, however, unknown confounders cannot be expected to be balanced between the cohorts and may influence the final result. Therefore, it is unclear whether it is the lifestyle or associated factors in persons who eat more fruit and vegetables or the foods themselves that offer protection from stroke. Although this study included only men, the protective effect of fruits and vegetables and lifestyle factors probably extends to women.

The article by Ascherio and colleagues is a report of a large cohort study from the Harvard group that suggests that increasing fish in the diet does not reduce the risk for coronary heart disease (CHD) in U.S. men of high socioeconomic status. The authors note, however, that the group eating no fish had the highest rate of cardiac events. Other primary prevention studies on this topic conflict (1-4). The beneficial vascular effects of omega n-3 fatty acids in fish may depend on serum eicosapentaenoic (EPA) and ocosahexaenoic (DHA) acids. Neither the serum levels of these active ingredients nor the methods of cooking the fish, which may affect the activity of these ingredients, were reported. A recent U.S. case-control study showed that the average U.S. consumption of fish did not result in substantial levels of EPA and DHA; this may have been because of the type of fish consumed or because of its preparation (5). Because this study also used a cohort design, confounding is possible. For example, men who ate more fish also appeared to be at higher risk for CHD (increased family history of CHD and cholesterol), were aware of this, led healthier lifestyles (which included increased exercise and consumption of fiber, fruit, vegetables, and vitamins), and had more cardiovascular bypass grafting.

Whether or not "a fish a day keeps the doctor away" is valid, studies from various sources point to the benefits of increasing fruits and vegetables in the diet of most persons. This is consistent with articles that suggest that increasing consumption of fiber and antioxidants may be beneficial to cardiovascular health.

Sonia Anand, MD
McMaster UniversityHamilton, Ontario, Canada
Stephen R. Yarnall, MD
Edmonds, Washington, USA


References

1. Kromhout D, Bosschieter EB, de Lezenne Coulander C. The inverse relation between fish consumption and 20-year mortality from coronary heart disease. N Engl J Med. 1985;312:1205-9.

2. Shekelle RB, Missell LV, Paul O, Shyrock AM, Stamler J. Fish consumption and mortality from coronary heart disease [Letter]. N Engl J Med. 1985;313:820.

3. Vollset SE, Heuch I, Bjelke E. Fish consumption and mortality from coronary heart disease [Letter]. N Engl J Med. 1985;313:820-1.

4. Norell SE, Ahlbom A, Feychting M, Pedersen NL. Fish consumption and mortality from coronary heart disease. Br Med J (Clin Res Ed). 1986;293:426.

5. Guallar E, Hennekens CH, Sacks FM, Willett WC, Stampfer MJ. A prospective study of plasma fish oil levels and incidence of myocardial infarction in U.S. male physicians. J Am Coll Cardiol. 1995;25:387-94.