Data from 16 studies including 402,127 individuals indicated that consuming five or more portions of fish per week was associated with a 13% reduction in the risk of all types of stroke.
Further analysis revealed that the risk of ischemic stroke – a form of stroke characterized by a clot in the brain – was reduced by 17% for the same level of consumption. The risk reduction for hemorrhagic stroke was not as large, added the researchers.
“It makes biological sense that fish intake was found to be inversely related to the risk of ischemic but not hemorragic stroke because of the different etiopathogenesis of these two stroke subtypes,” wrote the researchers in the European Journal of Clinical Nutrition.
“The antiplatelet activity of [long chain omega-3s] that protects against ischemic stroke development may be a risk factor for hemorrhagic stroke development. However, we did not observe an increased risk of hemorrhagic stroke in higher categories of fish consumption.”
Totality of the evidence
The new findings challenge to some extent a recent controversial meta-analysis that questioned the cardiovascular benefits of omega-3s published in JAMA (Vol. 308, pp. 1024-1033). That paper concluded that supplementation with omega-3 polyunsaturated fatty acids was not associated with a lower risk of cardiac death, sudden death, heart attack, or stroke.
The study was called ‘flawed’ by the omega-3 trade association GOED, and was said to have the potential to deter consumers from taking fatty acid supplements and being harmful to public health.
Led by scientists from the University of North Carolina at Chapel Hill, the scientists identified 16 studies for inclusion in the analysis. The average follow-up period for the studies was 12.8 years.
Results showed that increasing intakes of fish were linked to lower risks of stroke, and ischemic stroke, in particular.
Interestingly, the researchers report that this risk reduction link was only observed in studies conducted in the North America.
“Although it is reasonable to assume that the beneficial effect of fish intake on stroke risk comes from the [long chain omega-3] intake, a meta-analysis of nine randomized clinical trials published in 2006 did not find any effect of [long chain omega-3] intake on stroke risk.,” wrote the researchers.
“However, short-duration clinical trials based on patients focusing on fish oil supplement use cannot rule out a long-term beneficial effect of fish intake on the risk of stroke in the general population as found in this meta-analysis.
“Of note, it is also possible that the observed benefit of fish consumption is because of the nutrient package of whole fish. Therefore, studying [long chain omega-3] from fish intake alone might not fully explain the benefit of fish on stroke risk,” they added.
Commenting on the study's findings, Harry Rice, PhD, VP of regulatory and scientific affairs for GOED, told NutraIngredients-USA: "Given that stroke is a leading cause of death globally, the present results suggest that a public health campaign to stimulate fish intake in the general population may have a profound economic impact over time.
"This was a particularly interesting publication given the differentiation of studies between ischemic and hemorrhagic stroke."
Source: European Journal of Clinical Nutrition
Published online ahead of print, doi: 10.1038/ejcn.2012.133
“Fish consumption and risk of stroke and its subtypes: accumulative evidence from a meta-analysis of prospective cohort studies”
Authors: P Xun, B Qin, Y Song, Y Nakamura, T Kurth, S Yaemsiri, L Djousse and K He