Few people know that the human brain is comprised of over 60% fat or that its most abundant fat (25%) is called docosahexaenoic acid (DHA). DHA is an omega-3 long chain polyunsaturated fatty acid (not to be confused with the hormone DHEA). It is the primary structural fat in both the gray matter of the brain and the retina of the eye. DHA is essential for brain and eye development and function.
There are very few sources of DHA in the diet. It can be made from the omega-3 oil alpha-linolenic acid (ALA) found in large quantities in flax oil, in moderate amounts in canola oil and walnuts or in small amounts in green leafy vegetables. Only about 3-5% of the alpha-linolenic acid consumed becomes either DHA or EPA in healthy individuals. Neither DHA or EPA can be converted into the other in the body. This process of converting ALA to either DHA or EPA is hindered in various disease states and requires that some people receive DHA from their diet or supplementally. Healthy individuals who consume little DHA or EPA in their diet are creating what they need from ALA if their intake of ALA is adequate.
The average American’s diet, however, is now low in DHA resulting from a declining consumption of dietary sources of DHA such as fatty fish and animal organ meats. Vegetarians have lower blood levels of DHA and EPA due to its absence in foods of plant origin. Plant-based DHA supplements are available, and vegans should consider them if additional DHA is needed. Fish obtain both their DHA and EPA ultimately from the consumption of algae, which is also now more widely available to the public as the only “plant”-based source of DHA and EPA.
Fish oils contain both DHA and EPA in varying ratios, usually with about twice as much EPA as DHA. Some conditions should be treated predominantly with DHA and others mostly with EPA. Since DHA and EPA seem to compete with each other, taking a blend of the two has proven not to produce the expected benefits in some conditions. In other words, DHA should be taken separately from EPA in some conditions and a high EPA /DHA ratio product should be used in other conditions.
A study on elderly Japanese patients demonstrated that blood levels of the omega-3 fatty acids EPA and DHA increase after prolonged consumption of ALA from a plant-based oil. The change is slow and requires about 10 months of supplementation. However, the result of the study suggests that supplementation with ALA from flax oil may to some degree have the same beneficial role as supplementation with fish oil. This news may be particularly interesting to people following a vegetarian diet or for those who do not eat fish products.
Supplemental sources with high DHA/EPA ratios are now available that have been derived from algae. Sources with a high EPA/DHA ratio are derived from fish oils. Eggs are now available which contain EPA and DHA when the chickens have been fed special diets containing these fatty acids or flax seed. DHA doses are in the range of 500 to 2,500mg per day, depending on the condition being treated.