Eating Fish Can Postpone Cognitive Decline

Summarized by Robert W. Griffith, MD
August 14, 2007

Summary

Two well-conducted studies show that omega-3 fatty acids slow the decline of cognitive function over time. One solution could be eating one serving of fatty fish (mackerel, herring) or 5-6 servings of lean fish a week; if this is not possible, one can take one 1000 mg fish-oil capsule daily.

Introduction

Cognitive decline is the earliest sign of the onset of Alzheimer's disease - it represents a milestone between normal aging and full-blown Alzheimer's. Researchers are urgently looking for a drug or vaccine that can stop this slow but often inevitable process that is probably underway in 20% to 40% of all people over 85. While the cholinesterase inhibitors like donepezil (Aricept^®), rivastigmine (Exelon^®), and galantamine (Reminyl^®) can slow the process somewhat, they cannot arrest it. Now interest has turned to the effects of consumption of omega-3 fatty acids. Two studies have been published in the American Journal of Clinical Nutrition that show promise, and an editorial in the same journal forms the basis of this summary.

The Zutphen Elderly Study(1)

There were 210 participants in this Dutch study, who were men aged 70 to 89 at baseline in 1990. Dieticians interviewed the subjects in their homes at baseline and five years later, and calculated individual eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) intakes. Cognitive function was determined at baseline and after 5 years, using the Mini-Mental State Examination (MMSE). Demographic and lifestyle information was obtained, together with completion of a screening test for depression.

At baseline, 24% of the men didn't eat fish, 41% ate up to 20 grams of fish daily, and 35% ate more than 20 grams daily. The non-fish-eaters had an average EPA + DHA intake of 15 mg daily, from non-fish sources. At baseline, cognitive function did not differ between the three groups of men depending on how much fish they ate.

After 5 years, however, cognitive function had declined in the men who did not eat fish by 1.2 points on the MMSE scale, which was 4 times the decline in men who ate fish. There was a 'straight-line' correlation between fish eaten and cognitive decline, so that for every 380 mg/day of EPA + DHE intake there was a 1.1 MMSE point reduction in the rate of decline. This is roughly equivalent to one serving of fatty fish (mackerel, herring) a week, or 5-6 servings of lean fish a week.

The Atherosclerosis Risk in Communities (ARIC) Study(2)

The ARIC Study began in 1987-89 with the analysis of plasma fatty acids in the blood of over 2,200 Minneapolis residents. Three neuropsychological tests were given at baseline and again approximately 3, 6 and 9 years later; these examined delayed word recall, psychomotor speed, and verbal fluency, and allowed assessment of cognitive decline. Cutoff points for each of these tests were established, so that those participants who reached one or more of these three levels could be identified, as well as those showing overall deterioration.

Overall cognitive decline was more likely in participants with higher concentrations of palmitic and arachidonic acids - both omega-6 fatty acids. On the other hand, the risk of decline was lower in those with a higher concentration of linoleic acid - also an omega-6 fatty acid.

Cognitive decline was associated with lower omega-3 fatty acids (DHA + EPA) in the participants with high blood pressure and abnormal lipid levels; in particular, verbal fluency was reduced. However, there were no such changes in the participants as a whole.

Conclusions

In both these studies the omega-3 fatty acids slowed the decline of cognitive function over time; in the first, fish consumption was measured, and in the second, the fatty acid levels in the blood were determined. Taken together, the findings make it look conclusive that higher intake of DHA+EPA fatty acids will slow the decline in cognition that attacks many of us as we age.

How does this come about? It may be related to the known anti-thrombotic and anti-inflammatory properties of EPA. In addition, DHA may be able to correct a deficiency in brain-cell membranes seen in the cerebral cortex of Alzheimer's patients. The negative findings with palmitic acid are also interesting; this fatty acid is associated with thrombosis and elevated LDL-cholesterol levels, which might promote atherosclerotic changes in cerebral blood vessels.

Whatever the mechanism, the findings should provide the impetus for future prospective trials of fish, fish oil, or both, in elderly persons likely to develop Alzheimer's disease. In the meantime there's sufficient evidence to encourage older people to eat plenty of fish, preferably 'fatty' fish. Remember that omega-3 fatty acids slow cardiovascular decline, too; the American Heart Association recommends 2 servings of fatty fish a week. For those who are allergic to fish, or cannot obtain fish, the editorialists advise taking one fish-oil capsule (1000 mg) daily.

Source

• The importance of fish and docosahexaenoic acid in Alzheimer disease. Editorial. WE. Connor, SL. Connor, Am J Clin Med, 2007, vol. 85, pp. 929--930

Footnotes
1. Fish consumption, n-3 fatty acids, and subsequent 5-y cognitive decline in elderly men: the Zutphen Elderly Study. BM. van Gelder, M. Tijhuis , S. Kalmijn, D. Kromhaut, Am J Clin Nutr., 2007, vol. 85, pp. 1142--1147
2. Plasma n-3 fatty acids and the risk of cognitive decline in older adults: the Atherosclerosis Risk in Communities Study. MA. Beydoun, JS. Kaufman, JA. Satia,  et al., Am J Clin Nutr., 2007, vol. 85, pp. 1103--1111

Related Links
The Latest View on Omega-3 Fatty Acids
Eating Fish Can Help Prevent Alzheimer's (1)
Diagnosing Mild Cognitive Impairment

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