Everything about Docosahexaenoic Acid totally explained
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Docosahexaenoic acid (commonly known as
DHA; 22:6(ω-3),
all-cis-docosa-4,7,10,13,16,19-hexaenoic 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. 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's mounting evidence that DHA supplementation may be effective in combating such diseases (see external links at the end of this article).
Central nervous system constituent
DHA is the most abundant essential fatty acid (
polyunsaturated fatty acids, PUFAs) in the brain and retina. It comprises 40% of the PUFAs in the brain and 60% of the PUFAs in the retina. 50% of the weight of the
neuron's
plasma membrane is composed of DHA.
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.
Metabolic synthesis
In the human body, DHA is either present in the diet or it's derived from
eicosapentaenoic acid (EPA, 20:5, ω-3) via
docosapentaenoic acid (DPA, 22:5 ω-3) as an intermediate. This is done with an elongation step followed by the action of Δ4-
desaturase. Another pathway has also been described in
peroxysomes and
mitochondria. EPA is twice elongated yielding 24:5 ω-3, then desaturated to 24:6 ω-3, then shortened to DHA (22:6 ω-3) via
beta oxidation. This pathway is known as
Sprecher's shunt.
Health
Alzheimer's Disease
A large NIH drug trial is currently recruiting patients for evaluating DHA in Alzheimer's disease. This is the first human trial of DHA. Animal studies in the TG3 transgenic mouse model of Alzheimer's disease linked decreases in amyloid plaques and tau to dietary DHA. Animal studies also show that when combined with
arachidonic acid (also present in fish oil), the effectiveness of DHA for preventing plaques was less than without it.
Cancer
Researchers at the
University of Nevada conducted a study on the effects of DHA supplementation on the growth of human
colon adenocarcinoma in mice. The animals received one of four specialized diets: low-fat with corn oil (
omega-6 linoleic acid), high-fat with corn oil (omega-6 linoleic acid), high-fat with fish oil (
omega-3 EPA and DHA), and high-fat with algae-derived DHA (omega-3 DHA). At completion, the mice receiving a diet supplemented with algae-derived DHA had
tumors that were smaller than those of mice receiving diets supplemented with omega-3 from fish oil as well as those fed both the high- and low-fat corn oil (omega-6) diets. These results indicate that algae-derived DHA possesses greater tumor-suppressing properties than do corn or fish oil.
Pregnancy and lactation
DHA concentrations in
breast milk range from 0.07% to greater than 1.0% of total fatty acids, with a mean of about 0.34%. DHA levels in breast milk are higher if a mother's diet is high in fish.
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 are permitted in infant formula, as both are components of human breast milk. The addition of DHA at dose-effective levels has been shown to improve congitive function in both term and preterm infants.
DHA makes infant formula more like human milk than "conventional" formula containing
Alpha-linolenic acid and
linoleic acid, which are s to DHA. Formula sold in North America uses lipids from microorganisms grown in
bioreactors as sources of DHA.
Nutrition
Promotion as a food additive
DHA is actively promoted by manufacturers as a
food additive. Until recently, sales other than to makers of infant formula have been minimal; however, in 2007, several DHA-fortified dairy items (milk, yogurt) began selling in grocery stores.
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's less in eggs due to factory 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.
Algae-derived DHA in infant nutrition
Studies of vegans and vegetarians
Vegans and
vegetarians have markedly lower stores of DHA. Their bodily DHA levels don't 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.
Further Information
Get more info on 'Docosahexaenoic Acid'.
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