DHA Is Essential for Brain Function, Heart Health, and More
By Aaron W. Jensen, Ph.D.
Try to imagine the complexity of the human brain (go ahead - use your brain). It's a busy place, with about 100 billion cells working in concert to acquire, interpret, and store the ever-expanding information that surrounds you. It uses whatever mechanisms available - sight, sound, touch, taste, smell, intuition, reason, memory, imagination, conjecture - to expand its realm of knowledge, soaking up all that it can. There's a lot of information out there, and your brain wants to take in as much of it as possible.
Clearly your brain is an active organ, and it requires appropriate nourishment to maintain the one quadrillion (that's a million billion) connections between neurons that sustain its normal activity. Keep that in mind the next time you sit down to dine, and make sure you eat a healthy serving of brain food.
Omega-3s Are Good Fats
What is brain food? Amino acids qualify, as they provide the building blocks for many of the chemical messengers in the brain, called neurotransmitters. Glucose and oxygen in the blood ensure a continuous supply of energy to power your mental activities. And some of the most important nutrients upon which your brain depends turn out to be dietary fats, which have been shown to improve cognition, memory, and mood.
One of the dietary fats (technically, a fatty acid) most commonly associated with healthy brain function is docosahexaenoic acid (DHA), which belongs to the class of molecules called omega-3 fatty acids.* You may have heard of this compound in connection with coldwater fish, such as salmon, tuna, mackerel, halibut, and herring, which are the best dietary sources of DHA. That's one of the main reasons that coldwater fish are good for you.
*The name is derived from the molecular structure of these compounds. All of them consist of a long chain of carbon atoms to which only hydrogen atoms are attached. This type of structure repels water but is soluble in oil; these particular compounds are constituents of fats; hence they are called fatty. At one end of the carbon chain (the alpha end) is an acid group
DHA Is Vital for Cognitive Function
A number of clinical and research studies suggest that fats containing omega-3 fatty acids, in particular DHA, are vital for cognitive function, especially as we get older and our faculties tend to decline. Beyond cognition (the ability to perceive and interpret information correctly), DHA is essential for many other important brain functions. It has a significant impact on behavior and learning and is critical for proper neural development in infants and children. So coldwater fish really are brain food.
DHA is essential for cognition
and many other important brain
functions. It has a significant
impact on behavior and
learning and is critical for
proper neural development in
infants and children.
DHA is "conditionally essential," which means that, although it can be synthesized in the body, most of it must be obtained from food or dietary supplements. That's because the body's method of synthesis is inefficient, and it takes a long time to produce enough to satisfy cellular needs. By contrast, DHA from food or supplements can readily be incorporated into cells on an as-needed basis to promote improved health.
Omega-3s Prevent Cognitive Decline
A number of laboratory and clinical studies point to the importance of DHA in cognition. Over the years, several studies have documented that old animals supplemented with DHA have improved learning, memory, and problem-solving skills. So the natural question is whether these benefits translate to humans.
Dutch researchers addressed this question by monitoring the dietary habits of a large group of elderly men over a 3-year period.1 After analyzing all the dietary data, they concluded that a high intake of coldwater fish was inversely correlated with cognitive impairment. In other words, those men who consumed the greatest amount of fish (and thus, probably, the greatest amount of omega-3 fatty acids) were the least likely to suffer from age-related cognitive impairment.
DHA Protects Against Alzheimer's Disease
Additional research revealed that low serum DHA levels are a significant risk factor for the development of Alzheimer's disease (AD).2 This is consistent with the observation that the brains of AD patients typically have a lower DHA content than the brains of normal elderly adults. The researchers also found that low serum DHA levels appear to be common in other types of dementia and cognitive impairment related to aging.
It is difficult to pinpoint how DHA exerts its protective benefits for cognition and memory. One potential benefit, however, may be the ability of DHA to decrease damage to the cardiovascular system (see below). For example, localized cerebral infarcts (regions of dead tissue caused by an insufficient blood supply) may occur in the brain as a result of atherosclerosis (plaque deposits) and thrombosis (blood clots) in cerebral arteries. These infarcts can damage neurons involved in learning, memory, and cognition. The beneficial effects of omega-3 fatty acids on heart health may help prevent these kinds of problems and thus preserve cognitive function as a person ages.
DHA Protects Against Depression
Depression is a complex behavior, difficult to understand, but there is evidence that DHA plays an important role in this brain disorder as well. Research from a number of countries has demonstrated that depression is more common in patients with omega-3 fatty acid deficiencies. Not surprisingly, perhaps, countries with the lowest rates of fish consumption (and thus the lowest consumption of DHA) tend to have the highest rates of depression.3
When depressed individuals were instructed to increase their fish intake over a 5-year study period, the incidence of depression and hostility decreased dramatically. It has been suggested that repeated periods of emotional stress may be particularly taxing on DHA brain levels and that elevation of these levels through dietary intervention or supplementation may reduce stress-related behavioral changes.
DHA Helps Infant Vision and Intelligence
DHA is a vital component of phospholipids in cellular membranes and is especially prevalent in cells of the brain and the retina of the eye. Not surprisingly, DHA is important for neural and retinal development in infants. The importance of this compound is reinforced by the fact that it is the most abundant of the omega-3 fatty acids in human breast milk. This may help to explain the observation that breast-fed infants routinely score better on visual acuity and intelligence tests than those who were formula-fed. For this reason, DHA-supplemented infant formula has long been available in Europe and Japan. Fortunately, it is slowly appearing on U.S. supermarket shelves as well.
Not only is DHA beneficial during nursing, it is also essential during fetal development in pregnant women. Maternal DHA is capable of crossing over into the fetal circulation; it preferentially enters the developing fetus from the mother to participate in neural and retinal development. In fact, an English study has demonstrated that women who routinely ate fish during their pregnancy produced children whose visual acuity was better than that of formula-fed infants.4
Omega-3s Support Cardiovascular Health
While the benefits of DHA and other omega-3 fatty acids for cognitive development and other aspects of brain function are impressive, their role in supporting good cardiovascular health has received even more press lately. Omega-3 fatty acids from coldwater fish are associated with several benefits to cardiovascular health:
- Improving lipid profiles by reducing serum triglyceride levels
- Increasing the HDL/LDL ratio (the ratio of "good cholesterol" to "bad cholesterol")
- Stabilizing heart rhythm (by inhibiting cardiac arrhythmias)
- Inhibiting platelet aggregation (thereby reducing the risk of thrombosis)
- Reducing the risk of fatal heart attacks
Research on this topic, published recently in the New England Journal of Medicine, has revealed that men with the highest serum levels of omega-3 fatty acids had a reduced risk of sudden death from heart disease.5 Importantly, these men were all healthy at the beginning of the study and had no previous history of heart disease.
Using the data gathered over the 17-year period of the study, the researchers divided the men into four equal-sized groups, called quartiles, based on their omega-3 fatty acid levels. The men in the highest quartile (highest omega-3 levels) had an 81% lower risk of sudden death than those in the lowest quartile, and the men in the second-highest quartile had a 72% lower risk. Thus, for men with no evidence of prior cardiovascular disease, the message is clear: high omega-3 levels dramatically decrease the risk of sudden death from heart disease.
Omega-3s Help Prevent Heart Attack and Stroke
But what if you have already survived a heart attack - will omega-3 fatty acids still protect you against sudden death related to heart disease? According to a large international study, the answer is yes, although the protective benefit is not as great as it is with men who have no previous history of heart disease.6 Regardless, clinical trials employing omega-3 fatty acid supplementation or increased coldwater fish intake provide compelling evidence that increased consumption of omega-3 fatty acids reduces the occurrence of nonfatal and fatal heart attacks, and also reduces the risk of stroke.7
Clinical trials provide compelling
evidence that increased
consumption of omega-3 fatty acids
reduces the occurrence of nonfatal
and fatal heart attacks, and also
reduces the risk of stroke.
DHA Offers a Plethora of Health Benefits
The research on omega-3 fatty acids, and DHA in particular, is impressive. In addition to improving brain and heart function, there is evidence that DHA can reduce the symptoms of cancer and of inflammatory diseases such as rheumatoid arthritis (inflammation of joint tissue), asthma (caused in part by inflammation of bronchial air passages), and Crohn's disease (chronic inflammation of the intestinal wall).3 It is speculated that DHA may be able to moderate the production of inflammation-producing compounds and thus decrease the incidence of inflammation that leads to these debilitating diseases.
DHA has the potential to improve a number of serious health problems that afflict Americans. Our diets, however, are typically deficient in fish that are rich in omega-3 fatty acids, so we don't consume very much of these health-promoting compounds; in fact, we ingest only about 0.1-0.2 gram of omega-3 fatty acids daily, on average.8 This is significantly less than the recommended amount, which can be obtained by eating two to three servings of coldwater fish per week. For most people, however, that is an unreliable and expensive way to get their omega-3 fatty acids. Supplementation is much more reliable and convenient for those who seek DHA as a means to improve their cognitive function, heart health, mood, and more.
- Kalmijn S et al. Polyunsaturated fatty acids, antioxidants, and cognitive function in very old men. Am J Epidemiol 1997;145:33-41.
- Conquer JA et al. Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia, and cognitive impairment. Lipids2000;35:1305-12.
- Horrocks LA, Yeo YK. Health benefits of docosahexaenoic acid (DHA). Pharmacol Res 1999;40:211-25.
- Williams C et al. Stereoacuity at age 3.5 y in children born full-term is associated with prenatal and postnatal dietary factors: a report from a population-based cohort study. Am J Clin Nutr 2001;73:316-22.
- Albert CM et al. Blood levels of long-chain n-3 fatty acids and the risk of sudden death. New Engl J Med 2002;346:1113-8.
- GISSI-Prevenzione Investigators (Gruppo Italiano per lo Studio della Sopravivenze nell-Infarto Miocardico). Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet 1999;354:447-55.
- Burr ML et al. Effects of changes in fat, fish, and fibre intakes on death and myocardial reinfarction: diet and reinfarction trial. Lancet 1989;2:757-61.
- Kris-Etherton PM et al. Polyunsaturated fatty acids in the food chain in the United States. Am J Clin Nutr 2000;71 (Suppl):179-88S.
DHA May Improve Insulin Function in the Overweight
We Americans get plenty of fat in our diet. In fact, 30-35% of our calories come from fats (mostly of the worst kind), and there is a national epidemic of obesity. It's important to realize, however, that not all fats are bad. There are good fats, such as the monounsaturated and polyunsaturated fats found in olive oil and avocados, which should be regular components of our diet. And don't forget about omega-3 fatty acids, found in nature primarily in coldwater fish - they confer a plethora of health benefits and are obtained most reliably and conveniently in the form of supplements.
In a presentation at the Experimental Biology 2002 conference, Dr. Yvonne Denkins, from Louisiana State University, suggested that DHA may decrease insulin resistance in overweight individuals.1 She cited results from a preliminary study in which 12 overweight men and women, aged 40-70, were supplemented with 1.8 g of DHA daily for 12 weeks. The patients all suffered from insulin resistance, a condition that predisposes people to develop diabetes. At the end of the study period, 70% of the patients showed an improvement in insulin-related function, and in 50% it was a clinically significant change. These results are exciting, but they need to be validated by further research.
But why did the investigators undertake this study in the first place? Because they knew that the Inuit of Greenland, a population that is overweight owing to a fat-rich diet, have a surprisingly low incidence of both heart disease and diabetes. It turns out that they have a very high intake of omega-3 fatty acids, from all the fish they eat. Several years of study have pointed to the omega-3 fatty acids, such as DHA, as the agents that protect the Inuit from disease.
Dr. Jensen is a cell biologist who has conducted research in England, Germany, and the United States. He has taught college courses in biology and nutrition and has written extensively on medical and scientific topics.