Docosahexaenoic acid (commonly known as DHA; 22:6(ω-3), all-cis-docosa-4,7,10,13,16,19-hexa-enoic acid; trivial name cervonic acid) is an omega-3 essential fatty acid. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end.
Fish oils are rich in DHA. Most of the DHA in fish and more complex organisms originates in photosynthetic and heterotrophic microalgae, and becomes increasingly concentrated in organisms as it moves up the food chain. DHA is also commercially manufactured from microalgae; Crypthecodinium cohnii and another of the genus Schizochytrium. DHA manufactured using microalgae is vegetarian . Most animals make very little DHA through metabolism; however small amounts are manufactured internally through the consumption of α-linolenic acid, an omega-3 fatty acid found in chia, flax, and many other seeds and nuts.
DHA is metabolized to form the docosanoids—several families of potent hormones. DHA is a major fatty acid in sperm and brain phospholipids, and especially in the retina. Dietary DHA may reduce the risk of heart disease by reducing the level of blood triglycerides in humans. Low levels of DHA result in reduction of brain serotonin levels and have been associated with ADHD, Alzheimer's disease, and depression, among other diseases, and there is mounting evidence that DHA supplementation may be effective in combating such diseases (see external links at the end of this article).
Of all the fatty acids, DHA has the largest effect on brain PUFA composition. DHA is found in three phospholipids: phosphatidylethanolamine, ethanolamine plasmalogens, and phosphatidylserine (PS). It modulates the carrier-mediated transport of choline, glycine, and taurine, the function of delayed rectifier potassium channels, and the response of rhodopsin contained in the synaptic vesicles, among many other functions.
DHA deficiency is associated with cognitive decline. PS controls apoptosis, and low DHA levels lower neural cell PS and increase neural cell death. DHA is depleted in the cerebral cortex of severely depressed patients.
DHA has recently gained attention as a supplement for pregnant women, noting studies of improved attention and visual acuity. One recent study indicates that low levels of plasma and erythrocyte DHA were associated with poor retinal development, low visual acuity, and poor cognitive development. In that same study, alpha-linolenic acid was shown as a source of fetal DHA, but that performed DHA was more readily accredited. A working group from the ISSFAL (International Society for the Study of Fatty Acids and Lipids) recommended 300 mg/day of DHA for pregnant and lactating women, whereas the average consumption was between 45 mg and 115 mg per day of the women in the study. Other requirements are available from other sources.
DHA has been an ingredient in several brands of premium infant formula sold in North America since 2001 after Mead Johnson, the first infant formula manufacturer to add DHA and ARA (arachidonic acid) to its Enfamil Lipil product, received approval by the Food and Drug Administration and Health Canada. Both DHA and ARA, manufactured by Martek Biosciences Corporation, are permitted in infant formula. The addition of DHA at dose-effective levels has been shown to improve cognitive function in both term and preterm infants.
DHA makes infant formulas more like human milk than "conventional" formula containing Alpha-linolenic acid and linoleic acid, which are Precursors to DHA. Formula sold in North America uses lipids from microorganisms grown in bioreactors as sources of DHA.
There is less DHA available in the average diet than formerly, due to cattle being taken off grass and fed grain before butchering; likewise, there is less in eggs due to intensive farming. DHA is widely believed to be helpful to people with a history of heart disease, for premature infants, and to support healthy brain development especially in young children. Some manufactured DHA is a vegetarian product extracted from algae. Both types are odorless and tasteless after processing.
A study found that preterm infants fed baby formulas fortified with DHA derived directly from algae gained weight faster than infants fed formula fortified with DHA from fish oil. In addition, there are no risks of harmful contaminants such as methyl mercury or dioxins, which may be present in fish and fish oils. This is especially important for pregnant and nursing women and young children.
Vegans and vegetarians have markedly lower stores of DHA. Their bodily DHA levels do not rise much even with high dietary levels of linolenic acid. This, and features of the production and distribution of DHA in pregnant and lactating women, indicates that DHA per se is an essential nutrient. Since DHA is made by algae, there are vegan DHA supplements available.