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New Findings Boost Brain-Protecting Power of Fish
Study in older adults supports earlier evidence of anti-Alzheimer’s effects

10/10/2005 By Craig Weatherby

Want to shave a few years off your chronological age, at least in terms of mental performance? Try eating fish one or two times a week.

Researchers at Rush University Medical Center analyzed six years of data from 3,718-plus participants in the Chicago Health and Aging Project aged 65 or older.

After accounting for possible confounding factors—including healthy lifestyle behaviors—participants who ate fish once a week slowed their age-associated loss of mental function by 10 percent per year, and those who ate fish twice a week slowed their loss of function by 13 percent per year.

As the authors put it, "The rate reduction is the equivalent of being 3 to 4 years younger in age.”

How the study worked

Over the course of the six-year study, researchers (Morris MC, Evans DA, Tangney CC, et al) visited participants at home three times, to administer tests of mental performance, and ask about consumption frequency of 139 different foods, their daily activities, exercise level, alcohol consumption, mental activity, sex, race, education, income, and medical history.

The questionnaire asked about participants' consumption of tuna sandwiches, fried fish (sticks/cakes/sandwiches), and fresh fish as a main dish.  The respondents' consumption of shellfish (shrimp/lobster/crab) was recorded, but was not included in the calculation of weekly fish intake.

The results are considered especially reliable because the researchers administered multiple mental-performance tests over time: tactics designed to reduce bias and error.

Weak omega-3 link puzzles researchers

To their surprise, the Chicago researchers found no strong association between participants' estimated intake of omega-3 fatty acids and measured reductions in cognitive decline—except among those who'd eaten the most fish for the longest time. 

They were surprised because earlier studies have found that higher blood levels of omega-3s correlate to a reduced risk of Alzheimer's disease.

They proposed three possible reasons for the lack of a correlation between higher omega-3 consumption and delayed cognitive decline:

  • "The absence of association with [omega-3] DHA raises the possibility that the observed fish association was due to some other dietary constituent or perhaps to another factor that is related to cognitive health and fish consumption.
  • "We can only speculate that perhaps dietary -3 [omega-3] fatty acids have little impact on milder forms of cognitive decline.
  • "Another plausible explanation is that our measure of DHA and EPA intake is too imprecise to detect an association with cognitive change. One large population-based study examined the fatty acid composition of erythrocyte (blood-cell) membranes in relation to 4-year change in Mini-Mental State Examination score and observed significant reductions in cognitive decline with increased levels of total -3 fatty acids, DHA, and EPA.

Despite the lack of a connection in this study, the strong brain-protective effects of omega-3s seen in many other studies make it likely that they were also responsible for the benefits seen in this study.

And, some of the beneficial effects seen in these fish eaters may have stemmed from the fact that it replaced meats in their diets.  Red meats are high in the kinds of saturated fats that promote the vascular clogs linked to heart disease and dementia.


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