Fish and produce linked to better mental performance in healthy older people; omega-3s may suppress senility; American's omega-6-rich diets raise dementia risk
by Craig Weatherby
The results of most scientific investigations indicate that diets high in the long-chain “marine” omega-3 fatty acids found only in fish or fish oils are associated with a lower incidence of Alzheimer's disease and other forms of senile dementia (Issa AM et al 2006).
And the findings from four recent studies are especially encouraging because they investigated the association between fish or omega-3 intake and mental function in healthy people with no signs of dementia, aged 50 and older.
Three of the four studies were published in The American Journal of Clinical Nutrition, and as the author of an accompanying editorial wrote, these studies' positive outcomes offer “…the hope of preventing progression to states of dementia and disability before they become irreversible” (Rosenberg IH 2007).
A fourth study, from France, produced similarly hopeful fish-related findings in healthy older persons, and added fruits and vegetables to the dementia-prevention picture.
And the French investigation confirms the brain-risks associated with over-consumption of omega-6 fatty acids, which over-dominate American diets.
Here's what the four studies showed, in brief.
Study #1: Higher blood levels of omega-3s linked to better mental performance Researchers at the Netherlands' Maastricht University examined the fatty acid levels in 807 people aged 50 to 70, both at the beginning and the end of a three year period (Dullemeijer C et al 2007).
Likewise, the participants' mental acuity was determined at the beginning and end of the three-year period, using standard tests of memory, word fluency, and brain speed.
The Dutch team found that people with the highest blood levels of omega-3s enjoyed 69 percent less decline in sensorimotor speed (reaction time) and 60 percent less decline in overall brain speed, compared to those with the lowest omega-3 levels.
No associations were observed between omega-3 levels and the outcomes of tests gauging memory, information-processing speed, or word fluency.
Study #2: Higher omega-3 EPA levels, lower omega-6 levels enhance well-being
This study, conducted at New Zealand's University of Otago, looked for links between blood levels of omega-3s and participants' self-assessment of their mental and physical well-being (Crowe FL et al 2007).
The study involved 2,416 people who had completed health questionnaires and provided blood samples as part of New Zealand's 1997 National Nutrition Survey.
The “kiwi” scientists found that the subjects who had the highest proportions of EPA—one of the two major omega-3s in fish and fish oil—reported the highest levels of physical well-being.
And those who had the highest ratios of EPA to omega-6 arachidonic acid (AA) reported higher levels of mental well-being.
Why would higher levels of omega-3 EPA and lower levels of omega-6 AA enhance overall health?
Chronic inflammation undermines physical and mental health, and omega-3 EPA exerts an anti-inflammatory influence in the body, while an overabundance of omega-6 AA promotes chronic inflammation.
As the researchers put it, “The association between [EPA levels], the ratio of EPA to AA, and better self-reported physical well-being… has strong biological plausibility and warrants further investigation” (Crowe FL et al 2007).
Study #3: Fishy diets boost mental performance
Researchers at the University of Bergen, Norway looked for links between seafood consumption and mental performance in 2,031 elderly Norwegians (Nurk E et al 2007).
Participants who consumed at least 10 grams (1/3 of an ounce) of fish or seafood a day performed significantly better in brain-performance tests, compared with people who ate less than 10 grams daily.
And, significantly, the effect was “dose-dependent” which means that the best mental scores were seen among the participants who consumed about 75 grams (2.6 ounces) of fish per day.
The Norwegian team's conclusions were clear: “Most cognitive functions were influenced [positively] by fish intake.” And they noted an important distinction. “The effect was more pronounced for non-processed lean fish and fatty fish” (Nurk E et al 2007).
By “non-processed” fish, the Norwegian researchers meant fresh (or flash-frozen) fish, as opposed to the forms of processed fish most commonly consumed in America:
- Breaded/fried fish, whose coatings are typically high in brain-benefit-blunting omega-6 fatty acids;
- Conventional, twice-cooked canned tuna, which tends to have substantially lower omega-3 levels, compared with boutique, cooked-once brands (like ours).
But, surprisingly, the Norwegian team detected no added benefit from eating fatty fish as opposed to lean fish. This finding indicates that the benefits seen in the heavy fish-eaters stemmed from something other than omega-3 levels, per se.
As they wrote, “Studies of n-3 [omega-3] fatty acids, niacin, and any other factor known to be enriched in fish are needed to answer this question” (Nurk E et al 2007).
It is possible that absorption of the omega-3s in some lean, white fish may be enhanced by factors as yet undiscovered, such as the forms (triglyceride versus ethyl ester) or biochemical contexts (i.e., the structure of phospholipid “carriers”) in which omega-3s occur in different fish.
Study #4: Omega-3s reduce risk of Alzheimer's; Omega-6-rich diets raise the risk
A study from France affirms the preventive value of fish-borne omega-3s, and the risks of diets high in omega-6 fatty acids (Barberger-Gateau P et al 2007).
Omega-6 fatty acids predominate in our cheapest, most common vegetable oils—safflower, sunflower, corn, and soybean and prepared foods made with them—and in standard, grain-fed meats and poultry.
In 1999 and 2000, researchers at the French National Institute for Health and Medical Research (INSERM) recruited 8,085 people aged 65 and older in Bordeaux, Dijon, and Montpellier, for the “Three-City Cohort Study.
None of the participants showed signs of dementia upon examination at enrollment in the study, and each underwent at least one re-examination over the course of its four-year period.
At the end of the study, independent neurologists diagnosed 281 cases of dementia among the participants, including 183 cases of Alzheimer's disease.
Analysis of the study data revealed five key findings:]
- Participants who ate fish once a week or more were 35 percent less likely to have developed any form of dementia.
- Fish protected most participants against Alzheimer's disease, but did not protect the minority who carry a gene (ApoE4) that predisposes people to developing Alzheimer's. Most people lack this gene, so most of the participants benefited from fish.
- Participants who used vegetable oils high in omega-3s (canola oil, flaxseed oil, or walnut oil), were 54 percent less likely to have developed any form of dementia. However, these results were statistically weaker than the risk reductions recorded among fish lovers.
- Participants who ate fruits and/or vegetables daily were 28 percent less likely to have developed any form of dementia.
- Participants who lacked the ApoE4 gene, but ate diets were particularly high in omega-6s were more than twice as likely to have developed some form of dementia (112 percent more likely), unless their diets also included substantial amounts of omega-3s.
Their findings highlight the negative consequences of the standard American diet, which is high in omega-6 fats and low in “counterbalancing” omega-3s.
The best alternative oils are olive oil, macadamia nut oil, and special “high-oleic” sunflower oil, which are very low in omega-6s.
And meat from grass-fed livestock is much lower in omega-6s and higher in omega-3s, compared with the conventional, grain-fattened counterparts sold in most supermarkets.
- Barberger-Gateau P, Raffaitin C, Letenneur L, Berr C, Tzourio C, Dartigues JF, Alpérovitch A. Dietary patterns and risk of dementia: The Three-City cohort study. Neurology. 2007 Nov 13;69(20):1921-30.
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- Crowe FL, Skeaff CM, Green TJ, Gray AR. Serum phospholipid n 3 long-chain polyunsaturated fatty acids and physical and mental health in a population-based survey of New Zealand adolescents and adults. Am J Clin Nutr. 2007 Nov;86(5):1278-85.
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