Middle-aged people with the highest levels of omega-3 DHA had the highest brain-test scores; omega-3 EPA and ALA had no effect 05/04/2010
One indicated that diets high in omega-3 fatty acids may boost brain function by stimulating growth of grey matter in the brain.
And the second study suggested that having a higher-than-average ratio of omega-3 fats to omega-6 fats in the diet might boost intelligence and memory.
The study involved 280 middle-aged people and was designed to detect any statistical correlations between brain-test scores and the participants' blood levels of three different omega-3 fats: EPA and DHA from fish and ALA from plant foods (Muldoon MF et al. 2010).
In short, the participants with the highest blood levels of omega-3 DHA displayed the best brain performance.
In contrast, the researchers found no links between participants' brain performance and their blood levels of omega-3 EPA or ALA.
Importantly, the association between blood DHA levels and people's mental acuity was linear... the higher the DHA level, the higher the brain-test scores.
Because this was not a controlled clinical trial, its findings can only prove an association—not a cause-and-effect relationship—between omega-3 DHA and brain performance.
Prior clinical studies offer laregly positive but somewhat mixed evidence concerning the effect of various omega-3 fish oil products (containing EPA and/or DHA) on brain performance.
Just last week, we reported on a negative clinical trial... but that article links to some recent positive ones (see "Fish Oil for Elders… Is it a No-Brainer?”).
Before we describe the new study in a bit more detail, let's review the differences among the three omega-3 fats it examined in relation to brain health.
Two omega-3s called EPA and DHA are essential to human health and survival, and are found in almost every cell in the body.
While their roles overlap with regard to moderation of undesirable inflammation that promotes and prolongs many major disease processes, EPA seems to be the junior partner in brain function.
DHA constitutes most of the fat found in brain and eye cells... and, according to cell, animal, and human studies, it enables and enhances many more major brain-health functions than EPA does.
Fish and shellfish—especially fatty fish like salmon and tuna—are the only food sources of EPA and DHA (Algae and seaweed contain DHA, but the former is not a major food in any culture, and the amounts in seaweed are minuscule).
However, humans do not need to consume EPA or DHA to survive because our bodies can make both from a plant-source omega-3 fat called ALA.
The only good food sources of ALA are beans, flaxseed, walnuts, and leafy greens (e.g., spinach, kale, chard, and collard greens).
(Meats and poultry—especially products from grass-fed livestock—contain small amounts of ALA. But meats and poultry typically contain much more of an omega-6 fat called LA, which competes directly with ALA for conversion into the fatty acids needed by our bodies.)
But the process of converting ALA into EPA and DHA is very inefficient. Only two to 10 percent of dietary ALA gets turned into EPA and DHA. The conversion rate depends on a person's gender, age, genetics, diet, and other factors.
For example, the average young woman makes a bit more EPA and DHA from dietary ALA than the average man… probably because women give birth mostly in their teens and twenties and need to transfer lots of DHA to their babies for brain and eye development, first in utero, then in breast milk (Welch AA et al. 2008).
And people who eat no fish seem to convert ALA more efficiently than fish eaters do… probably because their bodies need EPA and DHA more urgently than do those of fish eaters, who get plenty from seafood and need to make little or none from the ALA in their foods (Welch AA et al. 2008).
Pittsburgh study links omega-3 DHA blood levels to better brain scores
The University of Pittsburgh team recruited 280 volunteers between 35 and 54 years of age, who were free of major psychiatric disorders and were not taking fish oil supplements (Muldoon MF et al. 2010).
The scientists, led by Matthew F. Muldoon, M.D., compared the volunteers' blood levels of three omega-3 fatty acids (EPA, DHA, and ALA) to their performance on a variety of neuropsychological tests designed to measure mental performance.
The tests covered five major dimensions of cognitive functioning, and a statistical analysis showed the volunteers with the highest DHA levels scored the highest on tests of non-verbal reasoning, mental flexibility, working memory, and vocabulary.
Additionally, the statistical links between higher DHA levels and higher scores on two of the tests (non-verbal reasoning and working memory) persisted after some participants' high scores were adjusted downward to account for the likely effects of having higher self-reported education levels and better vocabularies, as determined by higher scores on the vocabulary test.
And the volunteers' scores on none of the five tests bore any relation to their blood levels of EPA or ALA.
Thus, as the authors wrote, "only [omega-3] DHA is associated with major aspects of cognitive performance in adults less than 55 years old.
The Pittsburgh group went on to make the obvious point: "These findings suggest that DHA is related to brain health throughout the lifespan…”
- Muldoon MF, Ryan CM, Sheu L, Yao JK, Conklin SM, Manuck SB. Serum phospholipid docosahexaenonic acid is associated with cognitive functioning during middle adulthood. J Nutr. 2010 Apr;140(4):848-53. Epub 2010 Feb 24.
- Welch AA, Bingham SA, Khaw KT. Estimated conversion of alpha-linolenic acid to long chain n-3 polyunsaturated fatty acids is greater than expected in non fish-eating vegetarians and non fish-eating meat-eaters than in fish-eaters. J Hum Nutr Diet. 2008 Jul 15;21(4):404.