DHA from Fish Oil

Omega-3 Fatty Acids
Improve Cognitive Function

n Gulliver's Travels, Jonathan Swift described the Immortals from Luggnagg thus: ". . . they never can amuse themselves with reading, because their memory will not serve to carry them from the beginning of a sentence to the end . . . ." While the Luggnaggs may make your memory look sharp by comparison, it's probably still safe to bet that you forget where you put your car keys from time to time. After all, we all have our memory lapses.

The sad fact is that, as we age, our memory and our cognitive abilities in general are destined to decline. But much research demonstrates that certain fatty acids, especially the oils found in cold-water fish, can be used to improve brain function, reduce memory loss, and retard cognitive decline. One of these compounds is docosahexaenoic acid (DHA).

Scientists are still not sure how or why we age. But one thing is for sure - there's no way around getting older. As we age, we are more likely to forget birthdays, appointments, conversations, and other important information. This so-called age-related cognitive decline (ARCD) is marked by mild deterioration in our memory, our performance of simple daily tasks, and the speed of our mental processing.

Certain fatty acids, especially the
oils found in cold-water fish, can
be used to improve brain function,
reduce memory loss, and retard
cognitive decline.

The causes of ARCD are largely unknown, but recent research suggests that certain deleterious conditions or activities, such as high blood pressure, high levels of free radicals (reactive molecules that cause oxidative damage), metabolic disorders, smoking, low physical activity, and lack of mental challenge, may accelerate the rate of memory loss and mental decline.

But we don't have to sit back and take the aging process and its ensuing memory loss complacently. On the contrary, we can and should be proactive, taking advantage of current scientific research that suggests that we can prevent or retard ARCD. In this regard, it is instructive to consider the role that fats and fatty acids may play in improving cognitive function.

There appears to be a widespread public misconception about dietary fat. The plain truth is that the body and mind need dietary fat, in reasonable quantities, to function optimally (or even at all - without fat, we would die). Dietary fats are often referred to as fatty acids, which simply means that a long fat molecule has an acidic group attached to one end. These fats come 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 ones are usually oils.

Monounsaturated fats (e.g., olive, canola, 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.

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), 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. When they are transferred to a diet supplemented with DHA, however, they demonstrate dramatic improvement in learning and memory.2

Certain types of fish are rich in health-giving omega-3 fatty acids.
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

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. After only four days of supplementation, they need only half as much time to find their way out of a maze as control rats that were fed palm oil with no DHA.4 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 ARCD in humans.

We all realize that memory impairment is a natural part of growing older, and minor memory lapses are common. Cognitive decline as a result of aging can mean many different things. The type of information that is least easily recalled is generally nonessential and may simply reflect "forgetfulness." However, minor memory loss that progresses to a level where recent events are not remembered and everyday tasks are not performed properly may signal the onset of dementia.

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.

Dementia is a collective term that denotes memory loss along with a decline in intellectual functions, such as thinking and reasoning, in ways that interfere with normal activities such as cooking, household chores, and personal grooming. A persistent, steady decline in these areas may signal the onset of Alzheimer's disease, for example. (For more information on this terrible affliction, see "Preventing Dementia Can Boost Life Expectancy - Jun. 2001.)

A recent paper in the Archives of Neurology by Dr. Scott Small of Columbia University summarizes the relationships between cognition, age, and memory loss succinctly:5 "There is little question that memory declines with age. Although there is continued debate as to whether memory decline is normal, epidemiological data suggest that components of memory decline are not inevitable . . . ." Dr. Small further suggests that, as research progresses and the specific populations of neurons in regions of the brain responsible for memory loss are identified, more effective treatments for memory loss can be devised. One natural approach that we already know about for enhancing memory function is the omega-3 fatty acids present in fish oils.

Current research efforts have identified a number of potential memory boosters. Many of these are fish oils rich in omega-3 fatty acids, such as DHA. In fact, previous studies suggest that DHA levels in the brain decrease with advancing age6 and that humans with senile dementia treated for six months with fish-oil capsules (1400 mg of DHA per day) show improvement in intellectual function.7

A recent report demonstrates that the levels of DHA are lower in the brains of Alzheimer's patients than in those of normal elderly individuals. The DHA levels are typically lower in the blood plasma of AD patients also. These facts suggest that low DHA levels may be a risk factor for developing Alzheimer's disease.8

These facts suggest that low DHA
levels may be a risk factor for
developing Alzheimer's disease.

A separate study indicates that high fish consumption is positively correlated with cognitive function in older males.9 Researchers in Holland followed the dietary habits of 342 men from 1990 to 1993 and assessed their rate of cognitive decline during that period. Of a number of different dietary factors that were considered, only high fish consumption seemed to prevent a decrease in cognitive function over the study period.

Not all fish are equally beneficial in this respect. Cold-water fish, such as mackerel, herring, salmon, and tuna, have the highest levels of omega-3 fatty acids and contribute the largest amount of DHA to one's diet. A proposed recommended amount of DHA (combined with another fish oil, eicosapentaenoic acid, or EPA) is 0.65 g per day, which corresponds to two to three servings of cold-water fish per week.10 One study suggests that attaining this intake of DHA in the United States would require a quadrupling of our fish consumption.11 Since it is unlikely that this will happen anytime soon, if ever, the majority of our population will probably continue to receive an inadequate supply of omega-3 fatty acids.

Additional Benefits of Omega-3 Fatty Acids
Many different health benefits are attributed to the versatile omega-3 fatty acids.1 Various studies have shown that they can help:

  • Reduce the risk of heart disease and stroke
  • Improve retinal and brain development
  • Modulate some autoimmune diseases (such as lupus and some kidney disorders)
  • Reduce the risk of breast, colon, and prostate cancer
  • Reduce the symptoms of rheumatoid arthritis
  • Alleviate mild hypertension (high blood pressure)
  • Moderate Crohn's disease (a chronic inflammation of the intestinal wall)
  1. Connor WE. Importance of w-3 fatty acids in health and disease. Am J Clin Nutr 2000;71:171S-175S.

Although our bodies are capable of making DHA, this process is inefficient. The precursor to DHA is alpha-linolenic acid (ALA), a molecule that the body cannot synthesize, so it must be consumed in the diet (walnuts and soybeans are two of the better sources). But ALA is converted to DHA at a rate of only 3.8%.12 Given that Americans typically consume only 1.1-1.6 g of ALA per day (the recommended intake is 2.2 g), it is most unlikely that our bodies are getting sufficient amounts of DHA from that source.11 An inadequate supply of DHA may adversely affect organs such as the brain, eyes, and nervous system, which rely on this essential molecule.

There are a number of nutrients that are believed to contribute to boosting your memory function. Vinpocetine is a plant-derived compound that enhances blood circulation and oxygen and glucose utilization in the brain. Choline is a precursor to the neurotransmitter acetylcholine, which is vital for allowing nerve cells to communicate with one another and process stored information (memory). Citicoline is a more potent form of choline and has been shown to improve both immediate and delayed memory in older individuals. Pregnenolone enhances various aspects of brain chemistry, including acetylcholine function, thus also improving memory performance. Phosphatidylserine is a phospholipid (a fatty acid-containing compound) that has been found to improve cognitive function in patients with Alzheimer's disease. DMAE (dimethylaminoethanol) is known to enhance mood and alertness.

And, of course, there is the omega-3 fatty acid DHA, with so much animal research attesting to the importance of this molecule in brain development, cognition, and memory.

Advantages of a Mediterranean Diet
An additional approach to enhancing cognition may be to adopt a "Mediterranean diet" rich in unsaturated fatty acids. While such a diet has long been advocated by cardiologists and nutritionists for reasons of heart health, recent research indicates that it may decrease the rate of memory loss as well. A study of 278 elderly individuals (65-84 years of age) from Casamassima in rural southern Italy revealed a strong correlation between high monounsaturated fat intake and improved cognitive performance.1 On average, these individuals consumed 33% of their total calories in the form of fat, and 17.6% of their total calories came from monounsaturated fatty acids. Of the latter amount, 85% was derived from olive oil, which means that 15% of their total calories came from olive oil. These individuals exhibited a very low incidence of ARCD.

  1. Solfrizzi V, Panza F, Torres F, et al. High monounsaturated fatty acids intake protects against age-related cognitive decline. Neurology 1999;52:1563-9.


  1. Geiner 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:S239-S243.
  2. Gamoh S, Hashimoto M, Sugioka K, et al. Chronic administration of docosahexaenoic acid improves reference memory-related learning ability in young rats. Neuroscience 1999;93:237-41.
  3. Werkman SH, Carlson SE. A randomized trial of visual attention of preterm infants fed docosahexaenoic acid until nine months. Lipids 1996;31:91-7.
  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. Small SA. Age-related memory decline. Arch Neurol 2001;58:360-4.
  6. Suzuki H, Hayakawa S, Wada S. Effect of age on the modification of brain polyunsaturated fatty acids and enzyme activities by fish oil diet in rats. Mech Aging Devel 1989;50:17-25.
  7. Miyanaga K, Ynoemura K, Takagi T, et al. Clinical effects of DHA in demented patients. J Clin Ther Med 1995;11:881-901.
  8. Conquer JA, Tierney MC, Zecevic J, Bettger WJ, Fisher RH. Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia, and cognitive impairment. Lipids 2000;35:1305-12.
  9. Kalmijn S, Feskens EJ, Launer LJ, Kromhout D. Polyunsaturated fatty acids, antioxidants, and cognitive function in very old men. Am J Epidemiol 1997;145:33-41.
  10. Simopolous AP, Leaf A, Salem N Jr. Essentiality of and recommended dietary intakes for omega-6 and omega-3 fatty acids. Ann Nutr Metab 1999;43: 127-130.
  11. Kris-Etherton PM, Taylor DS, Yu-Poth S, et al. Polyunsaturated fatty acids in the food chain in the United States. Am J Clin Nutr 2000;71:179S-188S.
  12. Gerster H. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? Int J Vitam Nutr Res 1998;68:159-73.

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