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Meta-analysis supports fish, questions supplements, for stroke risk

By Stephen Daniells , 01-Nov-2012
Last updated on 01-Nov-2012 at 14:43 GMT

Regular consumption of fish may reduce the risk of coronary heart disease and stroke, but the benefits of fish oil supplements may be minimal, says a new analysis by researchers from high profile universities.

Analysis of data from 800,000 individuals in 15 countries indicated that five or more servings of fish per week were associated with a 12% reduction in the risk of cerebrovascular disease, compared with servings of one serving or less per week.

Results published in the British Medical Journal also indicated that the highest average intakes of omega-3 fatty acids, or from omega-3 supplement studies, only had a very small effect on disease risk.

Supplement findings change nothing

Challenging the conclusions about supplements, Harry Rice, PhD, VP of scientific and regulatory affairs for GOED, the omega-3 trade association, told NutraIngredients-USA that, with respect to supplementation, only 2 of 12 studies were conducted in healthy people. “The meta-analysis is really about individuals with cardiovascular disease,” he said.

“Curiously, the authors omitted a 2008 publication reporting on a sub-analysis of JELIS with respect to stroke incidence,” he said. “The results demonstrated a 20% relative reduction in recurrent stroke in the supplemented group. 

“The present results do not change the totality of the publicly available scientific evidence demonstrating cardiovascular benefits of EPA and DHA in healthy populations, as well as in the majority of populations with pre-existing cardiovascular ailments.

“Therefore, consumers should continue to eat fish, as well as take their omega-3 products for heart health.”

Study details

Led by Dr Rajiv Chowdhury at Cambridge University and Prof Oscar Franco at Erasmus MC Rotterdam, the researchers analyzed data from 38 studies with patients with established cardiovascular disease and lower risk people without the disease.

Results showed that two to four servings a week of fish were associated with a moderate 6% lower risk of cerebrovascular disease, compared with one or fewer servings of fish a week. Five or more servings a week had a 12% lower risk, they added.

On the other hand, levels of omega 3 fats in the blood and fish oil supplements were not significantly associated with a reduced risk, said the researchers.

“Our findings […] reinforce a potentially modest beneficial role of fish intake in the cause of cerebrovascular disease,” they wrote. “Such an advantage was less evident for long chain omega-3 fatty acids in both observational studies and interventions targeting primary and secondary stroke prevention.

“Our findings […] also underscore scientific gaps in the experimental evidence, specifically the lack of studies involving healthy populations and interventions targeting fish intake rather than using supplements, which may have different mechanistic effects.

“Additionally, adequately powered data from trials will be essential to investigate reliably the apparent higher risk of cerebrovascular disease observed in the secondary prevention trials of long chain omega 3 fatty acid supplements, and potential sex specific associations across observational studies.”

History

The heart health benefits of fish oil, and the omega-3 fatty acids it contains, are well-documented, being first reported in the early 1970s by Dr Jorn Dyerberg  and his co-workers in The Lancet and The American Journal of Clinical Nutrition.

To date, the polyunsaturated fatty acids (PUFAs) have been linked to improvements in blood lipid levels, a reduced tendency of thrombosis, blood pressure and heart rate improvements, and improved vascular function.

Source: British Medical Journal
2012: 345:e6698, doi: 10.1136/bmj.e6698
Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis”
Authors: R. Chowdhury, S. Stevens, D. Gorman, A. Pan, S. Warnakula, S. Chowdhury, H. Ward, L. Johnson, F. Crowe, F.B. Hu, O.H. Franco

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