Researchers found that older patients who ate at least three servings of fish a week had a decreased risk of certain subclinical brain abnormalities.

by Todd Neale, Staff Writer, MedPage Today 

KUOPIO, Finland, Aug. 5 — Older patients who ate at least three servings of fish a week had a decreased risk of certain subclinical brain abnormalities, researchers found.

Patients 65 and older who ate the most tuna or other fish high in omega-3 fatty acids tended to have a 26% reduced risk of silent infarct compared with those eating less than one serving a month (RR 0.74, 95% CI 0.54 to 1.01, P=0.06), Jyrki Virtanen, Ph.D., of the University of Kuopio, and colleagues reported in the Aug. 5 issue of Neurology.

In addition, those who ate the most fish had 10.6% better white matter grade scores compared with those who ate the least (P=0.003) after adjusting for various risk factors.

Action Points 

Explain to interested patients that this study found that the risk of a subclinical brain infarct was reduced with each serving of tuna or other fish high in omega-3 fatty acids consumed per week.

Point out that the study cannot rule out that the observed associations could be related to other factors such as differences in overall lifestyle, and that randomized clinical trials would be needed to determine causality.

The associations did not apply to consumption of fried fish, most likely because the types of fish usually fried — for example, cod and pollock — have low levels of omega-3 fatty acids.

Although fish consumption has been linked to reduced risk of clinical stroke, whether eating fish affects the risk of subclinical brain abnormalities — which are associated with cognitive and neurobehavioral impairments and increased risk of future stroke — is unknown, the researchers said.

To address the question, they turned to the Cardiovascular Health Study, conducted in four U.S. communities. They looked at data for 3,857 participants ages 65 and older who underwent at least one MRI scan; 2,116 of them underwent two scans five years apart.

All were free from clinical transient ischemic attack or stroke.

Fish consumption was measured using food frequency questionnaires, one administered at enrollment in 1989-1990 and the other during follow-up in 1995-1996.

Higher consumption of tuna or other broiled or baked fish was associated with younger age, female sex, higher education, lower systolic blood pressure, higher LDL and HDL cholesterol, higher ankle-arm index, higher energy intake, higher fruit and vegetable consumption, and lower saturated fat intake (P<0.05 for all).

On the first MRI, 23% of the participants showed at least one subclinical infarct, and on the second the prevalence was 23.1%.

For each additional serving of tuna or other non-fried fish consumed per week, the risk of subclinical infarct was reduced by 7% (P=0.03 for trend).

Among patients who had two scans performed, 16.6% had at least one new silent infarct between the two scans.

There was a nonsignificant trend toward a lower incidence of silent infarcts for those who ate the most fish. The lack of statistical significance was possibly related to limited power, the researchers said.

Fish consumption was not associated with sulcal or ventricular grades, markers of brain atrophy (P>0.10 for both).

Because consumption of fish or omega-3 fatty acids has also been associated with reduced risk of dementia and Alzheimer’s disease in other studies, the researchers said, “our findings suggest that prevention of subclinical infarcts and white matter abnormalities may be one mechanism whereby fish or [omega-3 fatty acid] consumption may decrease the development of these debilitating conditions.”

The authors acknowledged some limitations of the study, including the fact that participants who underwent MRI scans were healthier than those who did not, which might reduce the generalizability of the findings to the entire older population.

In addition, estimates of sulcal grade have high rates of inter-reader variability, the second food frequency questionnaire did not have information on fried fish consumption, estimating omega-3 fatty acid intake by questionnaire could have resulted in some exposure misclassification, and the food frequency questionnaires and MRI were not administered at the same time.

Finally, the associations could have been the result of other factors related to fish consumption, such as a healthier lifestyle.

Nevertheless, the researchers said, “our results support the need for randomized trials of fish or fish oil intake to reduce subclinical ischemic events, which would be feasible and important given the high incidence of such events in older adults.”

The study was supported by contracts from the National Heart, Lung, and Blood Institute, by the National Institute of Neurological Disorders and Stroke, and by grants from the Finnish Cultural Foundation, Helsingin Sanomar Centennial Foundation, Finnish Foundation for Cardiovascular Research, Yrjo Jahnsson Foundation, and University of Kuopio.

The authors made no disclosures.

Primary source: Neurology

Source reference: Virtanen J, et al “Fish consumption and risk of subclinical brain abnormalities on MRI in older adults” Neurology 2008; 71: 439-446.

Reviewed by Zalman S. Agus, MD; Emeritus Professor, University of Pennsylvania School of Medicine.

Published: August 05, 2008

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