Of the two principal Omega-3s, EPA and DHA …

Both body and mind need dietary fat in reasonable quantities to function properly

Of all the half-truths reported about dietary fats by the non-scientific press (including government “oracles”), none is greater than the notion that reduced consumption of fat is always good. This is contradicted by the inarguable fact that both body and mind need dietary fat in reasonable quantities to function properly and optimally (or even at all—without fat, we would die).

Dietary fats are frequently referred to as fatty acids, which simply means that a long fat molecule has an acidic group attached to one end. These fats exist in a variety of types, including saturated (meaning that there are no double bonds between carbon atoms in the chain), monounsaturated (one double bond), and polyunsaturated (two or more double bonds). If this seems overly technical, just remember that saturated fats, such as butter, tend to be solids at room temperature, and unsaturated fats are usually oils.

Monounsaturated fats (e.g., olive, canola, high oleic, and peanut oils) are generally considered to be healthier than polyunsaturated fats (e.g., sunflower, safflower, and corn oils). As we will see, however, members of a certain class of polyunsaturated fats—the omega-3 fatty acids—have many beneficial effects, particularly with respect to cognition and memory; they are also considered to be heart-healthy.

Dietary Fats Are Beneficial to Brain Function

It has long been known that dietary fats are beneficial to brain function. Brain tissue is especially rich in these vital nutrients, which help to ensure normal nerve-cell function, and the brain does not function optimally if it is deprived of them. For example, when laboratory rats are maintained on diets deficient in polyunsaturated fatty acids such as docosahexaenoic acid (it's an omega-3 fatty acid found in fish oil, aka DHA), their learning and memory capabilities are significantly impaired. 1 A separate study shows that rats initially maintained on a diet deficient in fish oil have poor learning and memory skills. 2 When they are transferred to a diet supplemented with DHA, however, they demonstrate dramatic improvement in learning and memory.

The omega-3 fatty acids have many 
beneficial effects, particularly with 
respect to cognition and memory; 
they are also considered to 
be heart-healthy.

DHA Tops other Fish Oils for Learning and Memory

DHA is one of the primary fatty acids found in fish oils. This molecule is very important in the formation of the cellular membranes of nerve cells. When DHA is in short supply, the structural and functional integrity of the nerve cell is compromised. Thus it is not surprising that a number of studies demonstrate that DHA is required for normal brain development in humans. In studies with infants, it has been found that newborns supplemented with DHA exhibit improved brain development, which allows them to process information more rapidly.3

DHA Shown to be Important for Older Animals

Much of the work with DHA thus far has been performed on laboratory animals and has focused on the memory of older animals. For example, when the diet of older rats is supplemented with DHA, their memory improves dramatically.4 After only four days of supplementation, they needed only half as much time to find their way out of a maze as control rats that were fed palm oil with no DHA. Based on this and other information, many researchers believe that an ample intake of omega-3 fatty acids such as DHA may be especially beneficial in protecting against age-related cognitive dysfunction in humans.

When DHA is in short supply, the 
structural and functional integrity of 
the nerve cell is compromised.

DHA Highest Concentrations in Brain and Eyes

The cell membranes of the neurons in your central nervous system contain large amounts of DHA (docosahexaenoic acid), which is one of the two most important omega-3 fatty acids. The other one being EPA (eicosapentaenoic acid). Although every cell in your body contains DHA, its highest concentrations are found in two organs you would not want to do without: your brain and your eyes (sperm is also rich in DHA).

DHA for Enhanced Neurotransmission

In your brain, DHA is found mainly in “excitable” cell membranes, i.e., those at the synaptic junctions between neurons, where neurotransmission takes place; it’s also found, however, in non-neuronal cells, such as glia.* In your eyes, DHA is found primarily in retinal pigment epithelial cells and in the photoreceptor cells of which the retina is primarily composed.

*Glia, or glial cells, are brain cells whose main function is to carry out a variety of support, transport, growth, and housekeeping tasks for the all-important neurons (there are about 50 glia for each neuron). It is believed, however, that glia may also be involved in the encoding and transfer of information in the brain.

DHA the Most Important Omega-3 in Your Brain

DHA is quantitatively the most important omega-3 in the brain, and consequently the most studied. The brain has a unique fatty acid composition with high levels of palmitate (16:0), the omega-6 PUFA arachidonic acid (AA, 20:4n-6), and DHA, but low levels of other omega-3, especially EPA. Indeed, brain EPA levels are typically 250–300 times lower than DHA.5 Thus, DHA is quantitatively the most important omega-3 in the brain.

Subjects whose serum PC-DHA 
was in the lower half of the 
distribution—but who did not have 
AD at the time the blood sample 
was taken—had a 67% greater 
likelihood of developing AD in 
the following ten years.

Low Serum DHA is a Risk Factor for Alzheimer’s

The circulating DHA status of 1,188 elderly American subjects (mean age 75) was determined using serum phosphatidylcholine (PC) in frozen plasma samples as the biomarker.6 Following the analysis of the blood samples, the researchers performed a blinded prospective analysis of the clinical outcomes over the next ten years.

In the individuals who had known Alzheimer’s disease (AD) at the time of taking the blood sample, there was a two-fold higher frequency (11 vs. 5) of AD in subjects from the lower half of the DHA distribution. Subjects whose serum PC-DHA was in the lower half of the distribution, but who did not have AD at the time the blood sample was taken, had a 67% greater likelihood of developing AD in the following ten years.

DHA May Improve Dementia Caused by Strokes

In Japan, stroke is an exceedingly common cause of disability and death. Japanese researchers tested the possibility that DHA supplements might improve mental functioning in patients with moderately severe dementia from thrombotic stroke.7 DHA is enriched in brain tissues and plays an important role in sensory functions. It also has electrical stabilizing effects and is antithrombotic.

In the central nervous system, DHA 
has unique and indispensable roles in 
neuronal membranes with levels 
preserved by multiple mechanisms.

Twenty male and female elderly patients (average age 83) with mild to moderate dementia due to stroke(s) were studied. The patients were divided into two groups, one of which received DHA, while the other received placebo. Each day, the DHA group received 6 DHA capsules (2 capsules taken three times a day) containing a total of 720 mg DHA daily for a year. In those with moderately severe dementia, DHA supplementation improved their dementia scores.

What We Now Know about DHA’s Role in the Brain

In a recent review, the researchers state that lipids are tightly linked to AD.8 They write that, “It has been shown that cholesterol increases amyloidogenic pathways and decreases non-amyloidogenic pathways followed by an enhanced Aβ production and aggregation. Opposite effects were observed for DHA, suggesting a potential beneficial role for DHA in AD.”

Published just a few months ago, a new review begins with an overview of omega-3 biochemistry and metabolism, with particular focus on the central nervous system, where DHA has unique and indispensable roles in neuronal membranes with levels preserved by multiple mechanisms.9


  1. Greiner RS, Moriguchi T, Hutton A, Slotnick BM, Salem N Jr. Rats with low levels of brain docosahexaenoic acid show impaired performance in olfactory-based and spatial learning tasks. Lipids. 1999;34 Suppl:S239-43.
  2. Chung WL, Chen JJ, Su HM. Fish oil supplementation of control and (n-3) fatty acid-deficient male rats enhances reference and working memory performance and increases brain regional docosahexaenoic acid levels. J Nutr. 2008 Jun;138(6):1165-71.
  3. Brenna JT, Carlson SE. Docosahexaenoic acid and human brain development: evidence that a dietary supply is needed for optimal development. J Hum Evol. 2014 Dec;77:99-106.
  4. Lim S-Y, Suzuki H. Intakes of dietary docosahexaenoic acid ethyl ester and egg phosphatidylcholine improve maze-learning ability in young and old mice. J Nutr. 2000;130:1629-32.
  5. Chen CT, Liu Z, Ouellet M, Calon F, Bazinet RP. Rapid beta-oxidation of eicosapentaenoic acid in mouse brain: an in situ study. Prostaglandins Leukot Essent Fatty Acids. 2009 Feb-Mar;80(2-3):157-63.
  6. Kyle DJ, Schaefer E, Patton G, Beiser A. Low serum docosahexaenoic acid is a significant risk factor for Alzheimer’s dementia. Lipids. 1999;34 Suppl:S245.
  7. Terano T, Fujishiro S, Ban T, et al. Docosahexaenoic acid supplementation improves the moderately severe dementia from thrombotic cerebrovascular diseases. Lipids. 1999;34 Suppl:S345-6.
  8. Grimm MO, Zimmer VC, Lehmann J, Grimm HS, Hartmann T. The impact of cholesterol, DHA, and sphingolipids on Alzheimer’s disease. Biomed Res Int.2013;2013:814390. doi: 10.1155/2013/814390. Epub 2014 Feb 19.
  9. Dyall SC. Long-chain omega-3 fatty acids and the brain: a review of the independent and shared effects of EPA, DPA and DHA. Front Aging Neurosci.2015 Apr 21;7:52. doi: 10.3389/fnagi.2015.00052. eCollection 2015.