Fish consumption linked to fewer ischemic strokes

Image: CC/James Heilman

Key findings:

1. There is a significant, though modest, decrease in the incidence of ischemic stroke associated with consuming fish at least once per week

Primer: The relationship between increased dietary fish consumption and the reduction in thromboembolic stroke events has been studied extensively, with reports linking the two since the 1990s. A possible link between a high-frequency of fish intake and an increased risk of hemorrhagic stroke has also been purported in the literature. These relationships have been attributed to omega-3 polyunsaturated fatty acids (n-3 PUFAs), which are relatively high in concentration in fish meat. These n-3 PUFAs have been shown to play a role in the inhibition of platelet aggregation and fibrinogen, the suppression of highly chemotactic leukotrienes, the reduction in markers of inflammation, and the overall improvement of insulin resistance. Although short-term fish oil supplementation has been shown to have no association with decreased stroke risk, studying the effects of n-3 PUFAs alone may not be indicative of the nutrient profile in whole fish. This present study standardizes whole fish consumption and evaluates potential heterogeneity by population and study characteristics.

For further reading, please see the following studies:

1. Keli SO, Feskens EJ, Kromhout D. Fish consumption and risk of stroke: The Zutphen study. Stroke 1994;25:328-332.
2. He K, Song Y, Daviglus ML, et al. Fish consumption and incidence of stroke: A meta-analysis of cohort studies. Stroke 2004;35:1538–1542.

This [meta-analysis] study: The data set for study of fish consumption and incident stroke included 19 cohorts from 16 prospective studies. The final analysis included 402,127 individuals between the ages of 30 and 103 years. After data pooling, consuming fish at least once a week was significantly associated with decreased incidence of ischemic stroke. None of the interactions between fish consumption and potential effect modifiers (i.e., location, follow-up length, and dietary assessment method) were statistically significant.

In sum: This meta-analysis demonstrated a significant, though modest, decrease in the risk of ischemic stroke associated with consuming fish at least once a week, when compared with individuals who consumed fish only once a month. There was no significantly increased benefit with consuming fish more than once a month, and no significant association with hemorrhagic stroke incidence.

Although the authors state that the studies chosen in this meta-analysis were well designed and adjusted for major lifestyle and dietary variables, it is likely that unmeasured factors had some level of influence in the primary outcomes of these studies. The only way to isolate the effect of fish consumption on stroke risk is through a randomized, controlled trial, which would arguably be difficult to achieve. It’s important to note also that the relative risk reduction that may be apparent with increased fish consumption would likely be precluded by the stroke-promoting “ingredients” of North American diets that result in the development of obesity, hypertension, and fluctuations in glycemic control. In the aforementioned studies, an overall healthy lifestyle of the fish consumers is what may account for the decreased risk of stroke. Nevertheless, since the North American diet is relatively low in n-3 PUFAs, regular intake of fish may incur some level of ischemic stroke protection.

Click here to read study in EJCN

Written by [JDP] and [AC]

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