Fish & omega-3 oils

There have been quite a few studies looking into the possible benefits of omega-3 fatty acids and fish (a good source of the oils), particularly for older adults. Several large studies have found that regular intake of oily fish is associated with lower rates of dementia — perhaps because, as one study found, it was associated with a much lower risk of silent brain infarcts. There is also some evidence that eating fish regularly slows the rate of 'normal' age-related cognitive decline.

One large Swedish study also found regular fish eating was associated with higher IQs in adolescent males.

Omega-3 fatty acids seem to help cognition by improving synaptic plasticity and the expression of several important proteins for learning and memory.

Although it's not yet clear which fatty acids are most important, one is definitely docosahexaenoic acid, or DHA. However, although this is available as dietary supplements, the evidence of its benefit in this form is much less clear. As usual, receiving them in food is much better. Salmon, mackerel, herring, sardines, and anchovies are all good sources (not, I am sorry to say, your standard fried fish from the chippie). Other sources include almonds, walnuts, soy, flaxseed oil, and eggs laid by chickens that eat DHA-supplemented feed.

A study involving 116 healthy older adults (65-75) has found that higher levels of several key nutrients in the blood were associated with more efficient brain connectivity and better cognitive performance. In fact, the findings suggest that the level of nutrients governs the strength of the association between functional brain network efficiency and cognitive performance.

The study looked at 32 key nutrients in the Mediterranean diet. The effective nutrients, which appeared to work synergistically, included omega-3 and omega-6 fatty acids, carotenoids, lycopene, riboflavin, folate, vitamin B12 and vitamin D.

A pattern of omega-3s, omega-6s and carotene was linked to better functional brain network efficiency.

Omega-3 fatty acids are abundant in fish, walnuts and Brussels sprouts; omega-6 fatty acids are found in flaxseed, pumpkin seeds, pine nuts and pistachios; lycopene is the vivid red pigment in tomatoes, watermelon and a few other fruits and vegetables; alpha- and beta-carotenoids give sweet potatoes and carrots their characteristic orange color.

A mouse study has found that canola oil in the diet was associated with worsened memory, worsened learning ability, and weight gain in Alzheimer's mice.

Canola oil-treated animals also had greatly reduced levels of amyloid beta 1-40 (the “good” version), leading to more amyloid-beta plaques (made from amyloid beta 1-42), and a significant decrease in synapses.

The mice were given the equivalent of about two tablespoons of canola oil daily. The mice began their enriched diet at 6 months of age, before they developed any signs of Alzheimer's.

A previous study by the same researchers found that Alzheimer’s mice fed a diet enriched with extra-virgin olive oil had reduced levels of amyloid plaques and phosphorylated tau and experienced memory improvement.

Moreover, olive oil reduced inflammation in the brain, improved synaptic integrity, and dramatically increased levels of autophagy (the process by which waste products from cells are cleared away).

A pilot study involving 106 participants of the Rush Memory and Aging Project who had experienced a stroke followed participants for an average of 5.9 years, testing their cognitive function and monitoring their eating habits using food journals. It was found that those whose diets scored highest on the MIND (Mediterranean-DASH Diet Intervention for Neurodegenerative Delay) diet score had substantially slower rates of cognitive decline than those who scored lowest. The estimated effect of the diet remained strong even after taking into account participants' level of education and participation in cognitive and physical activities. Those who instead scored high on the Mediterranean or DASH diets did not show the same slower decline.

Both the Mediterranean and DASH diets have been shown to be protective against coronary artery disease and stroke, but this finding suggests the MIND diet is better for overall brain health.

The MIND diet is a hybrid of the Mediterranean and DASH (Dietary Approaches to Stop Hypertension) diets. It has 15 components: 10 “brain-healthy food groups” and five unhealthy groups (red meat, butter, cheese, pastries and sweets, and fried or fast food).

To adhere to the MIND diet, you need to

  • eat at least three daily servings of whole grains
  • eat a green leafy vegetable and one other vegetable every day
  • drink a regular glass of wine
  • snack most days on nuts
  • have beans every other day or so
  • eat poultry and berries at least twice a week
  • eat fish at least once a week
  • limit butter to less than 1 1/2 teaspoons a day
  • eat less than 5 servings a week of sweets and pastries
  • eat less than one serving per week of whole fat cheese, and fried or fast food.

The researchers stress that this is a preliminary study, observational only. They are currently seeking participants for a wider, intervention study.

Laurel J. Cherian & Martha Clare Morris: Presentation at the American Stroke Association's International Stroke Conference 2018 in Los Angeles, January 25.

A study involving 266 people with mild cognitive impairment (aged 70+) has found that B vitamins are more effective in slowing cognitive decline when people have higher omega 3 levels.

Participants were randomly selected to receive either a B-vitamin supplement (folic acid, vitamins B6 and B12) or a placebo pill for two years. The vitamins had little to no effect for those with low levels of omega-3 fatty acids, but were very effective for those with high baseline omega-3 levels.

Levels of DHA appeared to be more important than levels of EPA, but more research is needed to confirm that.

The finding may help to explain why research looking at the effects of B vitamins, or the effects of omega-3 oils, have produced inconsistent findings.

The study followed research showing that B vitamins can slow or prevent brain atrophy and memory decline in people with MCI, and they were most effective in those who had above average blood levels of homocysteine.

I've spoken before about how the presence or absence of the “Alzheimer's gene” may affect which lifestyle changes are beneficial for you. A new study has added to that idea with a finding that seafood consumption was associated with fewer signs of Alzheimer's-related pathology, but only among those with the APOEe4 gene.

Seafood consumption was also associated with increased mercury levels in the brain, with levels rising the more seafood was consumed. However, higher levels of mercury were not correlated with any neuropathologies.

Fish oil supplementation was not associated with any differences in neuropathology. However, higher levels of alpha-linolenic acid (an omega-3 fatty acid found in flaxseed, chia seeds, walnuts, etc) were associated with a reduced chance of cerebral infarctions.

The study involved 554 deceased participants (average age 89.9 years) from the long-running Memory and Aging Project (MAP) conducted by Rush University Medical Center. The participants had completed annual dietary questionnaires over a number of years. The brains of 286 participants were autopsied, to assess neuropathologies and mercury levels.

The average educational attainment of the participants was 14.6 years; 67% were women.

The finding tempers the evidence from many studies that eating fish reduces Alzheimer's risk. However, it is consistent with what I believe is becoming apparent: that there are different paths to Alzheimer's, and thus different factors involved in preventing it, depending on your own particular gene-environment attributes.

Another study adds to the growing evidence that a Mediterranean diet is good for the aging brain.

The New York study used data from 674 non-demented older adults (average age 80). It found that those who closely followed such a diet showed significantly less brain shrinkage. Specifically, total brain volume was an average 13.11 milliliters greater, with grey matter volume 5 millilitres greater, and white matter 6.4 millilitres greater.

Eating at least five of the recommended Mediterranean diet components was associated with benefits equivalent to five years of age. By far the most important of these components was regular fish and reduced meat intake — at least 3 to 5 ounces of fish weekly; no more than 3.5 ounces of meat daily.

This is consistent with a considerable amount of research indicating the benefits of fish in fighting age-related cognitive decline.

A large, five-year study challenges the idea that omega-3 fatty acids can slow age-related cognitive decline. The study, involving 4,000 older adults, was part of the Age-Related Eye Disease Study (AREDS), which established that daily high doses of certain antioxidants and minerals can help slow the progression of age-related macular degeneration. However, a follow-up study found the addition of omega-3 fatty acids to the AREDS formula made no difference.

Omega-3 fatty acids are believed to be responsible for the health benefits associated with regularly eating fish, which is associated with lower rates of AMD, cardiovascular disease, and possibly dementia.

In this study, participants from the AREDS study, all of whom had early or intermediate AMD, were randomly assigned to either omega-3, or lutein and zeaxanthin (nutrients found in large amounts in green leafy vegetables), or both, or a placebo. As they all had AMD, participants also took the AREDS formula, which includes vitamins C, E, beta carotene, and zinc. Cognitive testing took place at the beginning, at 2 years, and at 4 years.

There was no benefit to these supplements: all groups showed a similar rate of cognitive decline over the study period.

The researchers speculate that the failure to find a benefit may lie in the age of the participants — it may be that supplements, to be of benefit, need to be started earlier. The other possibility (and the one I myself give greater weight to, although both factors may well be influential) is that these nutrients need to be taken in food to be effective.

It should be noted that the omega-3 fatty acids taken were those found in fish, not those found in plant foods such as flaxseed, walnuts, soy products, and canola and soybean oils.

Analyses of cerebrospinal fluid from 15 patients with Alzheimer's disease, 20 patients with mild cognitive impairment, and 21 control subjects, plus brain tissue from some of them, has found that those with Alzheimer’s had lower levels of a particular molecule involved in resolving inflammation. These ‘specialized pro-resolving mediators’ regulate the tidying up of the damage done by inflammation and the release of growth factors that stimulate tissue repair. Lower levels of these molecules also correlated with a lower degree of cognitive function.

The pro-resolving molecules identified so far are derivatives of omega-3 fatty acids, providing support for the idea that dietary supplements of these may provide benefit.

[3616] Wang, X., Zhu M., Hjorth E., Cortés-Toro V., Eyjolfsdottir H., Graff C., et al.
(2014).  Resolution of inflammation is altered in Alzheimer's disease.
Alzheimer's & Dementia.

The question of whether supplements of omega-3 fatty acids can help memory and cognition has been a contentious one, with some studies showing a positive effect and others failing to find an effect. My own take on this issue is that, like so many other things, it all depends on what you’re working with. It seems unsurprising if only those who have a deficient diet, or greater demands on their system (e.g., because of stress or age), or greater needs (e.g., because of a lack of cognitive reserve) might benefit from supplementation. A new study is a case in point.

The study involved 362 3rd, 4th, and 5th year students (mostly aged 7-9) from 74 schools, all of whom were reading poorly (in the lowest third). Participants were given 600 mg/day DHA (from algal oil), or a taste/color matched corn/soybean oil placebo. This was given in three capsules throughout the day, for 16 weeks.

The study found no significant improvement in reading or working memory for the DHA group as a whole, and although parents did report fewer behavioral problems, this was not confirmed by teachers.

However, there was a significant effect on reading if only those in the worst-performing 20% are considered (224 children), and an even greater effect if only those in the worst-performing 10% (105 children) are considered.

There was no significant effects for working memory, but I observe that this seems to be due to the much greater variability between individuals in the worst-performing groups (with this particularly evident in the bottom-10% group). It seems likely that whether or not DHA supplementation improves working memory capacity, depends on the factors affecting an individual’s WMC. Interestingly, a U.K. study that looked at the effects of omega-3 supplements on reading found highly significant benefits for those with Developmental Coordination Disorder.

The researchers do say that they had originally intended to look only at the poorest 20%, but decided to extend it to the lowest third when their participant numbers failed to reach the desired threshold (over half of the participant pool declined to take part).

The other point, of course, and typically for this research, is that participants only took the supplements for four months. We cannot rule out greater effects, and to a broader range of individuals, if they were taken for longer. There is also the question of compliance — compliance for those given at school was about 75% on average, and parental compliance is unknown.

In summary, I would say this is affirmation that omega-3 oils can be helpful for some individuals, but it shouldn’t be assumed that it’s a magic bullet for all.

[3069] Richardson, A. J., Burton J. R., Sewell R. P., Spreckelsen T. F., & Montgomery P.
(2012).  Docosahexaenoic Acid for Reading, Cognition and Behavior in Children Aged 7–9 Years: A Randomized, Controlled Trial (The DOLAB Study).
PLoS ONE. 7(9), e43909 - e43909.
Full text available at

Richardson AJ, Montgomery P (2005) The Oxford-Durham study: a randomized, controlled trial of dietary supplementation with fatty acids in children with developmental coordination disorder. Pediatrics 115: 1360–1366.

A review of three high quality trials comparing the putative benefits of omega-3 fatty acids for preventing age-related cognitive decline, has concluded that there is no evidence that taking fish oil supplements helps fight cognitive decline. The trials involved a total of 3,536 healthy older adults (60+). In two studies, participants were randomly assigned to receive gel capsules containing omega-3 PUFA or olive or sunflower oil for six or 24 months. In the third study, participants were randomly assigned to receive tubs of margarine spread for 40 months (regular margarine versus margarine fortified with omega-3 PUFA).

The researchers found no benefit from taking the omega-3 capsules or margarine spread compared to placebo capsules or margarines (sunflower oil, olive oil or regular margarine). Participants given omega-3 did not score better on the MMSE or on other tests of cognitive function such as verbal learning, digit span and verbal fluency.

The researchers nevertheless stress that longer term studies are needed, given that there was very little deterioration in cognitive function in any of the groups.

A new study, involving 1,219 dementia-free older adults (65+), has found that the more omega-3 fatty acids the person consumed, the lower the level of beta-amyloid in the blood (a proxy for brain levels). Consuming a gram of omega-3 more than the average per day was associated with 20-30% lower beta-amyloid levels. A gram of omega-3 equates to around half a fillet of salmon per week.

Participants provided information about their diet for an average of 1.2 years before their blood was tested for beta-amyloid. Other nutrients investigated —saturated fatty acids, omega-6 polyunsaturated fatty acids, mono-unsaturated fatty acid, vitamin E, vitamin C, beta-carotene, vitamin B12, folate and vitamin D — were not associated with beta-amyloid levels.

The results remained after adjusting for age, education, gender, ethnicity, amount of calories consumed and APOE gene status.

The findings are consistent with previous research associating higher levels of omega-3 and/or fish intake with lower risk of Alzheimer’s. Additionally, another recent study provides evidence that the brains of those with Alzheimer’s disease, MCI, and the cognitively normal, all have significantly different levels of omega-3 and omega-6 fatty acids. That study concluded that the differences were due to both consumption and metabolic differences.

[2959] Gu, Y., Schupf N., Cosentino S. A., Luchsinger J. a, & Scarmeas N.
(2012).  Nutrient Intake and Plasma Β-Amyloid.
Neurology. 78(23), 1832 - 1840.

Cunnane, S.C. et al. 2012. Plasma and Brain Fatty Acid Profiles in Mild Cognitive Impairment and Alzheimer’s Disease. Journal of Alzheimer’s Disease, 29 (3), 691-697.

A rat study has shown how a diet high in fructose (from corn syrup, not the natural levels that occur in fruit) impairs brain connections and hurts memory and learning — and how omega-3 fatty acids can reduce the damage.

We know that these unnaturally high levels of fructose can hurt the brain indirectly through their role in diabetes and obesity, but this new study demonstrates that it also damages the brain directly.

In the study, two groups of rats consumed a fructose solution as drinking water for six weeks. One of these groups also received omega-3 fatty acids in the form of flaxseed oil and DHA. Both groups trained on a maze twice daily for five days before starting the experimental diet. After the six weeks of the diet, the rats were put in the maze again.

Those who didn’t receive the omega-3 oils navigated the maze much more slowly than the second group, and their brains showed a decline in synaptic activity. They also showed signs of resistance to insulin. Indications were that insulin had lost much of its power to regulate synaptic function.

It’s suggested that too much fructose could block insulin's ability to regulate how cells use and store sugar for the energy required for processing information.

It’s estimated that the average American consumes more than 40 pounds of high-fructose corn syrup per year.

The findings are consistent with research showing an association between metabolic syndrome and poorer cognitive function, and help explain the mechanism. They also support the consumption of omega-3 fatty acids as a preventative or ameliorative strategy.

A study involving 1,575 older adults (aged 58-76) has found that those with DHA levels in the bottom 25% had smaller brain volume (equivalent to about 2 years of aging) and greater amounts of white matter lesions. Those with levels of all omega-3 fatty acids in the bottom quarter also scored lower on tests of visual memory, executive function, and abstract thinking.

The finding adds to the evidence that higher levels of omega-3 fatty acids reduce dementia risk.

For more about omega-3 oils and cognition

The study involved 104 healthy older adults (average age 87) participating in the Oregon Brain Aging Study. Analysis of the nutrient biomarkers in their blood revealed that those with diets high in omega 3 fatty acids and in vitamins C, D, E and the B vitamins had higher scores on cognitive tests than people with diets low in those nutrients, while those with diets high in trans fats were more likely to score more poorly on cognitive tests.

These were dose-dependent, with each standard deviation increase in the vitamin BCDE score ssociated with a 0.28 SD increase in global cognitive score, and each SD increase in the trans fat score associated with a 0.30 SD decrease in global cognitive score.

Trans fats are primarily found in packaged, fast, fried and frozen food, baked goods and margarine spreads.

Brain scans of 42 of the participants found that those with diets high in vitamins BCDE and omega 3 fatty acids were also less likely to have the brain shrinkage associated with Alzheimer's, while those with high trans fats were more likely to show such brain atrophy.

Those with higher omega-3 scores also had fewer white matter hyperintensities. However, this association became weaker once depression and hypertension were taken into account.

Overall, the participants had good nutritional status, but 7% were deficient in vitamin B12 (I’m surprised it’s so low, but bear in mind that these are already a select group, being healthy at such an advanced age) and 25% were deficient in vitamin D.

The nutrient biomarkers accounted for 17% of the variation in cognitive performance, while age, education, APOE genotype (presence or absence of the ‘Alzheimer’s gene’), depression and high blood pressure together accounted for 46%. Diet was more important for brain atrophy: here, the nutrient biomarkers accounted for 37% of the variation, while the other factors accounted for 40% (meaning that diet was nearly as important as all these other factors combined!).

The findings add to the growing evidence that diet has a significant role in determining whether or not, and when, you develop Alzheimer’s disease.

There have been mixed findings about the benefits of DHA (an omega-3 fatty acid), but in a study involving 485 older adults (55+) with age-related cognitive impairment, those randomly assigned to take DHA for six months improved the score on a visuospatial learning and episodic memory test. Higher levels of DHA in the blood correlated with better scores on the paired associate learning task. DHA supplementation was also associated with better verbal recognition, but not better working memory or executive function.

Other research has found no benefit from DHA to those already with Alzheimer’s, although those with Alzheimer’s tend to have lower levels of DHA in the blood. These findings reinforce the idea that the benefit of many proactive lifestyle strategies, such as diet and exercise, may depend mainly on their use before systems deteriorate.

The daily dose of algal DHA was 900 mg. The study took place at 19 clinical sites in the U.S., and those involved had an MMSE score greater than 26.

Low levels of DHA, an omega-3 fatty acid, have been found in the brains of those with Alzheimer's disease, but the reason has not been known. A new study has found that lower levels of DHA in the liver (where most brain DHA is manufactured) were correlated with greater cognitive problems in the Alzheimer’s patients. Moreover, comparison of postmortem livers from Alzheimer’s patients and controls found reduced expression of a protein that converts a precursor acid into DHA, meaning the liver was less able to make DHA from food.

The findings may explain why clinical trials in which Alzheimer's patients are given omega-3 fatty acids have had mixed results. They also suggest that it might be possible to identify at-risk persons using specific blood tests, and perhaps delay the development of Alzheimer’s with a chemically enhanced form of DHA.

A European trial involving 225 patients with mild Alzheimer's has found that those who drank Souvenaid (a cocktail of uridine, choline and the omega-3 fatty acid DHA, plus B vitamins, phosopholipids and antioxidants) for 12 weeks were more likely to improve their performance in a delayed verbal recall task. 40% of the Souvenaid group showed improved performance compared to 24% of the placebo group. Those with the mildest cases of Alzheimer’s showed the most improvement. There was no improvement on the more general ADAS-cog test. Three further clinical trials, one in the U.S. and two in Europe, are now underway.

Scheltens, P. et al. 2010. Efficacy of a medical food in mild Alzheimer's disease: A randomized, controlled trial. Alzheimer's & Dementia, 6 (1), 1-10.

The largest ever trial of fish oil supplements has found no evidence that they offer benefits for cognitive function in older people. The British study enrolled 867 participants aged 70-80 years, and lasted two years. After two years, those receiving fish oil capsules had significantly higher levels of omega-3 fatty acids in their blood than those receiving placebo capsules. However, cognitive function did not decline in either group over the period. The researchers caution that it may be that more time is needed for benefits to show.

Seventh graders given 20 mg zinc, five days per week, for 10 to 12 weeks showed improvement in cognitive performance, responding more quickly and accurately on memory tasks and with more sustained attention, than classmates who received no additional zinc. Those who received only 10mg a day did not improve their performance. Previous studies have linked zinc nutrition to motor, cognitive and psychosocial function in very young children and adults, but this is the first study of its effect in adolescents. Adolescents are at particular risk of zinc deficiency, because they are undergoing rapid growth and often have poor eating habits. Red meats, fish and grains are good sources of zinc.

The findings were presented at Experimental Biology 2005, as part of the scientific sessions of the American Society of Nutritional Sciences.

A study of over 3,100 older men (49-71) from across Europe has found that men with higher levels of vitamin D performed consistently better in an attention and speed of processing task. There was no difference on visual memory tasks. Although previous studies have suggested low vitamin D levels may be associated with poorer cognitive performance, findings have been inconsistent. Vitamin D is primarily synthesised from sun exposure but is also found in certain foods such as oily fish.

A review described as “definitive” has concluded that there is ample biological evidence to suggest an important role for vitamin D in brain development and function, and that supplementation for groups chronically low in vitamin D is warranted. Vitamin D has long been known to promote healthy bones, but more recently has been found to have a much broader role — over 900 different genes are now known to be able to bind the vitamin D receptor. Evidence for vitamin D's involvement in brain function includes the wide distribution of vitamin D receptors throughout the brain, as well as its ability to affect proteins in the brain known to be directly involved in learning and memory and motor control. Because we receive most of our Vitamin D from sunlight (UV from the sun converts a biochemical in the skin to vitamin D), those with darker skin living in northern latitudes are particularly at risk of vitamin D deficiency. Nursing infants and the elderly are also particularly vulnerable. It has also argued that current recommendations set the recommended level of vitamin D too low. This review is the fourth in a series that critically evaluate scientific evidence linking deficiencies in micronutrients to brain function. Earlier reviews have looked at DHA, choline, and iron.

A "cocktail" of dietary supplements (omega-3 fatty acids, uridine and choline) has been found to dramatically increase the amount of membranes that form brain cell synapses in gerbils. The treatment is now in human clinical trials. It is hoped that such treatment may significantly delay Alzheimer's disease. The treatment offers a different approach from the traditional tactic of targeting amyloid plaques and tangles. Choline can be found in meats, nuts and eggs, and omega-3 fatty acids are found in a variety of sources, including fish, eggs, flaxseed and meat from grass-fed animals. Uridine, which is found in RNA and produced by the liver and kidney, is not obtained from the diet, although it is found in human breast milk.

A study has found that gerbils given a ‘cocktail’ of DHA, uridine and choline performed significantly better on learning and memory tests than untreated gerbils, and their brains had up to 70% more phosphatides (a type of molecule that forms cell membranes) than controls, suggesting that new synapses are forming. Some of the gerbils received all three compounds and some received only two; the improvements were greatest in those given all three. An earlier study had found that the treatment improved function in rats with cognitive impairment. Omega-3 fatty acids are found in fish, eggs, flaxseed and meat from grass-fed animals. Choline is found in meats, nuts and eggs. Uridine cannot be obtained from food sources, but is a component of human breast milk and can be produced in the body.

A mouse study has found that the diet of a pregnant mother, especially in regards to choline, can change the epigenetic switches that control brain development in the fetus. Pregnant mice received different diets during the period when a fetus develops its hippocampus. The genetic changes affected neurogenesis. The findings add to other research pointing to the effects of maternal diet on fetal development. Top sources of choline are eggs and meat. Fish and soy are also good sources.

Older news items (pre-2010) brought over from the old website

Mixed results from trials of DHA

A large 18-month trial of the effects of DHA, an omega 3 fatty acid, on 402 people with mild to moderate Alzheimer's found no evidence of benefit. However, there were indications that those without the “Alzheimer’s gene” ApoE-e4 showed slower cognitive decline. A 6-month trial involving 485 healthy seniors with mild memory complaint also found a benefit on a test of memory and learning.

Quinn, J.F. et al. 2009. A clinical trial of docosahexaenoic acid (DHA) for the treatment of Alzheimer's disease. Presented at the Alzheimer's Association International Conference on Alzheimer's Disease July 11-16 in Vienna.

Yurko-Mauro, K. et al. 2009. Results of the MIDAS Trial: Effects of Docosahexaenoic Acid on Physiological and Safety Parameters in Age-Related Cognitive Decline. Presented at the Alzheimer's Association International Conference on Alzheimer's Disease July 11-16 in Vienna.

Fish eating associated with higher IQ scores in teenage boys.

IQ records from some 4000 Swedish males at 18 who had also taken part in a survey of fish consumption at age 15 has revealed that those who ate fish once a week at 15 had IQ scores 7% higher (on average) than those who didn’t eat fish that often. Those who ate fish more than once a week showed an improvement of 12%. The effect was independent of education.

[1018] Åberg, M AI., Åberg N., Brisman J., Sundberg R., Winkvist A., & Torén K.
(2009).  Fish intake of Swedish male adolescents is a predictor of cognitive performance.
Acta Pædiatrica. 98(3), 555 - 560.

Intake of certain fatty acid appears to improve neurodevelopment for preterm girls, but not boys

A large randomized trial of infants born at less than 33 weeks' gestation from five Australian hospitals has found that girls who received a high supplementary daily dose of DHA (an omega-3 fatty acid) in either their breast milk or infant formula until their expected delivery date performed significantly better on a mental development test when they were 18 months old than girls who received a low dose. However, bafflingly, boys showed no effect.

[402] Smithers, L. G., Willson K., Ryan P., Makrides M., Gibson R. A., McPhee A. J., et al.
(2009).  Neurodevelopmental Outcomes of Preterm Infants Fed High-Dose Docosahexaenoic Acid: A Randomized Controlled Trial.
JAMA. 301(2), 175 - 182.

Eating fish may prevent memory loss and stroke in old age

A large study involving 3,660 people age 65 and older over five years, has found that those who ate broiled or baked tuna and other fish high in omega-3 fatty acids three times or more per week had a nearly 26% lower risk of having silent brain infarcts that can cause dementia and stroke, compared to people who did not eat fish regularly. One serving a week reduced risk by 13%. Regular fish consumption was also associated with fewer changes in white matter. Types of fish that contain high levels of DHA and EPA nutrients include salmon, mackerel, herring, sardines, and anchovies. Eating fried fish was not protective. Silent brain infarcts are only detected by brain scans, and are found in about 20% of otherwise healthy elderly people.

However, in the same journal, another study reports findings that in a double-blind, placebo-controlled, study of 302 healthy older adults, 26 weeks of EPA-DHA supplements had no effect on cognitive performance. Of course, if the effect of fish oil is primarily on preserving brain health, it may well be (indeed is likely) that the study was too short to impact cognitive performance. It is also possible that supplements are not as effective as whole foods — many studies have found that it is much more effective to receive needed vitamins and minerals through nutrition rather than supplementation.; Reference

[265] van de Rest, O., Geleijnse J. M., Kok F. J., van Staveren W. A., Dullemeijer C., OldeRikkert M. G. M., et al.
(2008).  Effect of fish oil on cognitive performance in older subjects: A randomized, controlled trial.
Neurology. 71(6), 430 - 438.

[308] Virtanen, J. K., Siscovick D. S., Longstreth W. T., Kuller L. H., & Mozaffarian D.
(2008).  Fish consumption and risk of subclinical brain abnormalities on MRI in older adults.
Neurology. 71(6), 439 - 446.

How food affects the brain

I’ve reported on quite a lot of studies finding beneficial effects of one food or another on the brain. Now a researcher has analyzed more than 160 studies about food's affect on the brain, and here’s the bottom line. He comes out for omega-3 fatty acids, as both improving synaptic plasticity and the expression of several molecules proteins to learning and memory, as well as protecting against attention-deficit disorder, dyslexia, dementia, depression, bipolar disorder and schizophrenia. He suggests it’s better to get it from food than supplements (which is always recommended). Salmon, walnuts and kiwi fruit are all good sources. They’re still working out which fatty acids are most important, but one is definitely docosahexaenoic acid, or DHA — which like vitamin C we’re not good at making for ourselves; we have to ingest it. He also concludes that diets high in trans fats and saturated fats are bad for cognition.
Studies also support the need for folic acid (found in spinach, orange juice and yeast), which is essential for brain function, and appears to reduce age-related cognitive decline and dementia. And BDNF, important for learning and memory as well as metabolic regulation (so there’s a connection there with obesity), is helped by omega-3 fatty acids and the curry spice curcumin, and also, it seems, smaller food portions.

[1293] Gómez-Pinilla, F.
(2008).  Brain foods: the effects of nutrients on brain function.
Nat Rev Neurosci. 9(7), 568 - 578.

Full text is available online at

Omega-3 boosts grey matter

A study of 55 healthy adults has found that those who had high levels of long-chain omega-3 fatty acids had more grey matter in areas of the brain associated with emotional arousal and regulation — the bilateral anterior cingulate cortex, the right amygdala and the right hippocampus. Although this doesn’t mean omega-3 necessarily causes such changes, the finding does support a recent study that found higher levels of omega-3 were associated with a more positive outlook, and animal studies showing that increasing omega-3 intake leads to structural changes in the brain. Good sources of omega-3 fatty acids are walnuts, flax, and fatty fish such as salmon and sardines.

The findings were presented March 7 at the American Psychosomatic Society's 2003 Meeting, in Budapest, Hungary.

Higher level of certain fatty acid associated with lower dementia risk

A nine year study of 899 participants in the Framingham Heart Study (average age 76 years) has found that those with the highest levels of an omega-3 polyunsaturated fatty acid known as docosahexaenoic acid (DHA) had a 47% lower risk of developing dementia and 39% lower risk of developing Alzheimer's. Among the participants who completed the dietary questionnaire, those in this top quartile of blood DHA levels reported that they ate an average of .18 grams of DHA a day and an average of three fish servings a week. Those in the other quartiles ate substantially less fish.

[2408] Schaefer, E. J., Bongard V., Beiser A. S., Lamon-Fava S., Robins S. J., Au R., et al.
(2006).  Plasma Phosphatidylcholine Docosahexaenoic Acid Content and Risk of Dementia and Alzheimer Disease: The Framingham Heart Study.
Arch Neurol. 63(11), 1545 - 1550.

Omega-3 fatty acids may slow cognitive decline in some patients with very mild Alzheimer's disease

Several studies have shown that eating fish, which is high in omega-3 fatty acids, may protect against Alzheimer's disease. A Swedish study has now tested whether supplements could have similar effects. Patients with mild-to-moderate Alzheimer’s who took 1.7 grams of DHA and .6g of EPA showed the same rate of cognitive decline as those taking a placebo, however, among a subgroup of 32 patients with very mild cognitive impairment, those who took the fatty acids experienced less decline in six months compared with those who took placebo. It may be that anti-inflammatory effects are an important reason for the benefit, potentially explaining why effects were seen only in those with very early-stage disease, when levels of inflammation seem to be higher.

[2401] Freund-Levi, Y., Eriksdotter-Jonhagen M., Cederholm T., Basun H., Faxen-Irving G., Garlind A., et al.
(2006).  {omega}-3 Fatty Acid Treatment in 174 Patients With Mild to Moderate Alzheimer Disease: OmegAD Study: A Randomized Double-blind Trial.
Arch Neurol. 63(10), 1402 - 1408.

Eating fish associated with slower cognitive decline

Analysis of data from an ongoing longitudinal study of older adults has found that the rate of cognitive decline over a six-year period was reduced by 10-13% in those who ate fish at least once a week.

[534] Morris, M C., Evans D. A., Tangney C. C., Bienias J. L., & Wilson R. S.
(2005).  Fish Consumption and Cognitive Decline With Age in a Large Community Study.
Arch Neurol. 62(12), 1849 - 1853.

Fish oil may help prevent Alzheimer's

A study involving genetically engineered mice has found that a diet high in docosahexenoic acid, or DHA — an omega-3 fatty acid found in relatively high concentrations in cold-water fish — dramatically slowed the progression of Alzheimer's, by cutting the harmful brain plaques that mark the disease. An earlier study showed that DHA protected against damage to the "synaptic" areas where brain cells communicate and enabled mice to perform better on memory tests. Food sources of omega-3 fatty acids include fish such as salmon, halibut, mackerel and sardines, as well as almonds, walnuts, soy, and DHA-enriched eggs.

Lim, G.P., Calon, F., Morihara, T., Yang, F., Teter, B., Ubeda, O., Salem, N.Jr, Frautschy, S.A. & Cole, G.M. 2005. A Diet Enriched with the Omega-3 Fatty Acid Docosahexaenoic Acid Reduces Amyloid Burden in an Aged Alzheimer Mouse Model. Journal of Neuroscience, 25(12), 3032-3040.

Omega-3 fatty acid may prevent Alzheimer's disease and slow its progression

A study using genetically engineered mice has shown that a diet high in the omega-3 fatty acid DHA helps protect the brain against the memory loss and cell damage caused by Alzheimer's disease. Cheap sources of DHA include coldwater fish, like salmon, halibut, mackerel, sardines and herring. These fish consume algae, which is high in DHA. Because these fishes' oiliness makes them absorb more mercury, dioxin, PCP and other metals, however, a less risky yet more costly strategy is to consume fish oil or purified DHA supplements made from algae. Other options include DHA-rich eggs laid by chickens that eat DHA-supplemented feed.

[2397] Calon, F., Lim G. P., Yang F., Morihara T., Teter B., Ubeda O., et al.
(2004).  Docosahexaenoic Acid Protects from Dendritic Pathology in an Alzheimer's Disease Mouse Model.
Neuron. 43(5), 633 - 645.

Eating fish cuts risk of dementia

Using data from a French epidemiological study of cognitive and functional aging, researchers found that those who ate fish or seafood at least once a week had a significantly lower risk of being diagnosed as having dementia (including Alzheimer’s) over the seven years follow-up. This confirms earlier findings from the Rotterdam Study, which had a much shorter follow-up (a mean of 2.1 years). There was an association between level of education and diet which partly, but not completely, explains this. It does appear that this is a benefit from eating fish / seafood, possibly from the fatty acids found in fish oils. There was no significant association between meat consumption and risk of dementia.

Barberger-Gateau, P., Letenneur, L., Deschamps, V., Pérès, K., Dartigues, J. & Renaud, S. 2002. Fish, meat, and risk of dementia: cohort study. BMJ, 325, 932-933.

What about mercury?

No strong evidence linking mercury levels with worse cognitive performance in older adults

We are encouraged to eat fish for its health benefits, but there has been some concern about mercury levels. Now the first study of mercury and cognitive function in 1140 urban U.S. adults between the ages of 50 and 70 years has found that blood mercury levels were not consistently associated with adverse performance on a broad range of tests of cognitive function. Most of the large number of tests showed no correlation with mercury and there was a lack of consistency of mercury effects in different aspects of brain function.

[1313] Weil, M., Bressler J., Parsons P., Bolla K., Glass T., & Schwartz B.
(2005).  Blood Mercury Levels and Neurobehavioral Function.
JAMA. 293(15), 1875 - 1882.

Eating methylmercury contaminated fish causes problems in adults

Pregnant women and children have been warned about eating methylmercury contaminated fish. New research now suggests that all adults should be wary. The study involved 129 men and women living in fishing communities of the Pantanal region of Brazil. About one out of four were found to have mercury levels that exceeded the 'safe' level set by the World Health Organization for women and children. Those individuals fared worse on tests for motor skills, memory and concentration.
The major source of methylmercury is diet, particularly large fish like shark and swordfish.

[1423] Yokoo, E. M., Valente J. G., Grattan L., Schmidt S L., Platt I., & Silbergeld E. K.
(Submitted).  Low level methylmercury exposure affects neuropsychological function in adults.
Environmental Health. 2, 8 - 8.
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