Omega-3 Fatty Acids: The Role of DHA

Omega-3 fatty acids are a group of polyunsaturated fatty acids that play a variety of important roles in health. EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are two of the most important omega-3 fatty acids, and are commonly found together in seafood and in fish oil supplements.Polyunsaturated fatty acids are composed of a chain of carbon atoms with two or more double bonds. The number and placement of these double bonds are what make EPA and DHA unique. DHA has 6 double bonds and 22 carbons. EPA has 5 double bonds and 20 carbons. DHA tends to improve cell membrane fluidity much more than EPA, allowing for nerve synapses to transmit signals more quickly and with greater effectiveness.While DHA and EPA most often function together, DHA plays a starring role in several crucial areas. Because DHA has a longer carbon chain and a higher degree of unsaturation, it has unique structural and functional properties in cell membrane phospholipids, particularly those in the retina and the neuronal synapses in the brain. Important DHA functions include:Brain and Neurodegenerative DiseasesApproximately 60% of the brain is made of lipids (fats) with DHA being one of the most prevalent fatty acids in the brain. An emerging body of research is exploring a unique role for DHA in neurodevelopment and the prevention of neuropsychiatric and neurodegenerative disorders. Low DHA levels are found in the brains of people with neurogenerative diseases like Alzheimer’s. As the disease becomes more severe, DHA levels continuously decrease. Supplemental DHA has shown some success in decreasing the cognitive decline associated with dementia, especially in people who do not routinely consume seafood naturally high in DHA. There is also some evidence that consuming DHA may improve working memory in young adults.Pregnancy and Infant DevelopmentDHA is crucial for optimal development and function of the brain and retina in the fetus and infants.DHA availability to the fetus is dependent on the mother’s diet, with DHA levels higher in women who consume seafood more often. Infants need DHA, especially during the first 6 months of their lives, so that their brains, eyes, and nervous systems develop optimally. The Institute of Medicine (IOM) established an Adequate Intake (AI) of total omega-3 fatty acids for infants from birth to 12 months that is equivalent to the mean intake of omega-3s in healthy, breastfed infants. The IOM did not establish specific intake recommendations for EPA or DHA. Starting in 2002, DHA and arachidonic acid (the two most prevalent long chain polyunsaturated fatty acids in the brain) were added to most infant formulas available in the United States so that they more closely mimic the fatty acid content of breast milk.VisionDHA plays a crucial role in the growth and development of vision in infants, and it may also contribute to improved vision as we age. One study of adults age 45-77 discovered that supplementing the diet with DHA for 90 days led to better vision than placebo.Reproductive HealthAlmost 50% of infertility cases are attributed to male infertility, and research is focusing on the potential role of polyunsaturated fatty acids in promoting male fertility. DHA is present in larger amounts in testicular cells and sperm, and it appears that infertility rates are higher in men with low levels of DHA in their sperm. However, there is no conclusive evidence that increasing DHA from foods or supplements leads to improved fertility.Cardiovascular DiseaseIt’s well-established that fish oil containing both EPA and DHA has a protective effect against cardiovascular disease. Some research shows that DHA lowers triglyceride levels more than EPA, increases the particle size of LDL, and increases HDL levels to reduce risk of cardiovascular disease. DHA also may have a greater impact on reducing cardiac arrhythmia than EPA.Anti-Inflammatory EffectsDHA plays a role in reducing inflammation that is associated with several chronic conditions, including arthritis and ulcerative colitis. One European study showed that people with the highest consumption of DHA had a 77% reduced risk of developing ulcerative colitis. Consuming more DHA may also decrease joint swelling and pain found in arthritis.Food sources of DHAOmega-3 fatty acids, including both EPA and DHA, are found primarily in cold-water fish including salmon, tuna, lake trout, sardines, herring, crabs, mussels and oysters. Seaweed also contains DHA. Our body is able to synthesize EPA from plant foods including flaxseeds, canola oil, walnuts, and soy foods, but DHA must be consumed directly from food sources.Meat from wild animals contains significantly higher levels of DHA than meat from domesticated animals. Free-range, pasture-fed or organically-raised meats have not been shown to contain higher amounts of DHA. Because of the research on the potential health benefits of DHA, foods such as milk, bread, and eggs are often fortified with DHA from seaweed and fish oil. DHA and EPA are also available in fish oil supplements, and DHA supplements alone are made from seaweed. Most omega-3 fatty acid research uses 1,000 to 2,500 mg of DHA per day. Read the label on fish oil supplements since the amount of EPA and DHA varies. Be sure to talk with your physician before taking fish oil or DHA supplements.By Lynn Grieger, RDN, CDE, CPT, CHWCReferences

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