Fish consumption has been associated with a decrease in ischemic stroke and an increase in hemorrhagic stroke, possibly through inhibition of platelet aggregation. He and colleagues conducted a prospective cohort study to determine whether eating fish or supplementation with long-chain omega-3 polyunsaturated fatty acids (PUFA) reduces the risk of ischemic but not hemorrhagic stroke.

The Health Professional Follow-Up Study is a cohort of male health care professionals aged 40 to 75 years who responded to a comprehensive diet and lifestyle questionnaire every two to four years. A total of 43,671 men were followed from 1986 to 1998. Participants quantified their fish intake, and the researchers grouped responses using a frequency scale ranging from less than once per month to at least five times per week. PUFA intake was estimated according to a previously established U.S. Department of Agriculture database.

A total of 608 participants developed stroke during the study period; 377 cases were confirmed ischemic strokes, 106 were confirmed hemorrhagic strokes, and the remainder could not be classified using information in the medical records. When cumulative fish consumption was assessed, the risk of ischemic stroke was lower for participants who ate at least one serving of fish per month compared with those who ate fish less often than once per month. As few as one to three servings of fish per month were associated with a significant reduction in ischemic stroke, with no added benefit at higher levels of consumption. The risk for hemorrhagic stroke was not significantly affected by fish intake.

In the analysis of recent fish intake, the results were similar to those of the cumulative-intake analysis but somewhat attenuated. In the analysis of long-chain omega-3 PUFA intake, the risk of ischemic stroke was significantly reduced in all but the highest categories of intake compared with the lowest category, with no associated increase in hemorrhagic stroke. Alpha-linoleic acid intake had no apparent impact on stroke, nor were the findings materially modified when participants took aspirin or vitamin E.

In summary, the authors observed a 40 percent lower risk of ischemic stroke in men who ate fish at least once per month compared with men who had less frequent consumption of fish, with a maximal benefit at about one serving per week. Although inhibition of platelet aggregation is a hypothesized mechanism for this protective effect, aspirin use did not modify the impact of fish consumption. The authors conclude that eating at least one serving of fish per month reduces the risk of ischemic stroke in men. Further research is needed to determine whether fish consumption is associated with increased risk of hemorrhagic stroke.