Nutrition, deficiency & diseases: Docosahexaenoic acid

Mar 2014 Home › Fats deficiency › Docosahexaenoic acid

Docosahexaenoic acid (DHA) is a polyunsaturated 22-carbon omega-3 conditionally essential fatty acid. In humans, DHA is not an essential fatty acid (EFA) as it can be synthesized from dietary alpha-linolenic acid (ALA).

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However it is essential for many biochemical and metabolic functions of the brain and the body. Docosahexaenoic acid is an important structural fat component of the human brain, cerebral cortex, spermatozoa, dermis, testes and retina. Food sources of DHA are maternal milk, fish oil, algae and krill.

In the absence of sufficient dietary ALA or in an inability of the body to synthesize DHA from ALA due to defective DHA-synthesizing enzyme, dietary sources of docosahexaenoic acid becomes essential for the functions of the organs of the human body, especially brain.

Structure and properties of docosahexaenoic acid

DHA is an organic carboxylic acid characterized by the presence of carboxyl group. It has 22-carbon chain and six cis double bonds. The first double bond is located at the third carbon from the omega end. Its systematic name is all-cis-docosa-4,7,10,13,16,19-hexa-enoic acid. The IUPAC name of docosahexaenoic acid is (4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenoic acid; Doconexent.
Trivial name of DHA is cervonic acid and its shorthand name in the nomenclature of FA is 22:6(n-3).

It is a weak acid with a boiling point of 446.7 °C. Its molecular formula is C₂₂H₃₂O₂.
The chemical structure of DHA is:

Chemical structure of docosahexaenoic acid (DHA)

Docosahexaenoic acid synthesis

DHA is synthesized in the body by ALA metabolism.
It is synthesized from eicosapentaenoic acid (EPA) via docosapentaenoic acid as an intermediate.
By the Sprecher's shunt pathway EPA is elongated twice to yield 24:5 ω-3.
It is then desaturated to 24:6 ω-3.
24:6 ω-3, via beta oxidation is shortened to 22:6 ω-3 (DHA).

DHA for brain

Docosahexaenoic acid is the major fat in the brain phospholipids.
It is required for the healthy development of brain in the infants.
In adults it is very much required for the proper brain functions.
Depression, attention-deficit hyperactivity disorder (ADHD), cognitive decline, dementia, Alzheimer's disease and decline of mental health have been associated with the deficiency of this FA.
In stroke patients, supplementation has been found to decrease the brain damage and speed up recovery.

DHA and pregnancy

Dietary docosahexaenoic acid is important for the developing fetus and for healthy breast milk in nursing mothers.
In United States majority of pregnant women consume between 45 mg and 115 mg of docosahexaenoic acid per day in their diets, whereas the recommended level is 300 mg per day.
Babies of women taking supplements of this FA during pregnancy have been found to have greater resistance against cold.

Low plasma levels of DHA have been associated with poor retinal development, low visual acuity, and poor cognitive development.
The concentration of this FA in the breast milk is around 0.34% of the total fats present.
If the mother's diet is high in fish, the average increases.

DHA health benefits

Docosahexaenoic acid is very essential for all the neurological functions of the brain.
Use of the fish oil supplements during pregnancy improves the neurological development of the fetus as well as ensuring the sufficiency of the omega-3 fat in the breast milk.
Dietary docosahexaenoic acid, by reducing the level of blood triglycerides, reduces the risk of cardiovascular diseases.
It is a major fat component of retina and accounts for 60% of PUFA in retina. Patients with retinitis pigmentosa are found to have very low levels of this FA.
In persons taking the supplements of this FA there is marked decrease in the concentrations of several inflammatory markers in their blood.
Apart from increasing the efficacy of chemotherapy in prostate cancer, it is found to inhibit human colon carcinoma growth.
Considering the benefits to the heart, the American Heart Association recommends eating fatty fish, at least twice a week.
Several studies have indicated that fish oil helps in reducing the pain symptoms and inflammation associated with rheumatoid arthritis.
When the supplement is taken regularly, the pain of menstrual cramps is reduced.

DHA food sources

Cold water fish and fish oils are rich sources of docosahexaenoic acid. According to USDA cooked salmon contain 500–1500 mg DHA per 100 grams. Mackerel, anchovies, lake trout, herring, sardines, tuna, bluefin tuna and swordfish are other rich food sources for this FA. For infants breast milk is the best source. Fish oils, algae-based, vegetable-like oil and fish liver oils are also good food sources.

DHA side effects

In some persons, consuming fish oil, may cause side effects like belching, nausea, upset stomach and diarrhea.
Docosahexaenoic acid can increase the bleeding time and persons taking blood-thinning medication/anticoagulants should take the supplements with caution.
Patients undergoing treatment for hypertension should consult a doctor before taking fish oil supplement as along with BP medication it can cause low blood pressure.
As the fish oil supplements can lower the blood sugar, in persons taking diabetes medicine, blood sugar levels may get too low.

DHA supplements

Major supplements of these omega-3 fats are fish oil, algal oil and krill oil. Docosahexaenoic acid fortified milk, yogurt, cooking oil etc are being made available. Docosahexaenoic acid single-cell oil (DHASCO) is being added in infant feed supplements. Vegan diets do not contain this FA and the product extracted from algae is considered as a vegetarian source. Very low levels of docosahexaenoic acid in fetus and breast milk in vegans is of great concern.

DHA fish oil

Fish oil is sold in gelatin capsules containing a mixture of omega-3 family containing both EPA and docosahexaenoic acid, the later being present in smaller quantities. As the fish caught in the polluted seas can accumulate the heavy metals like mercury their use for fish oil extraction is harmful to the users. There has to be a testing mechanism all over the world for these fish products.

Algal DHA

NASA sponsored scientific research lead to the discovery of algae-based docosahexaenoic acid. This algae-based, vegetable-like oil contains docosahexaenoic acid and ARA. Other Vegetarian sources come from seaweeds. Farm raised algae are sustainable source of the omega-3 fats. These algal products can carry a vegetarian label and also certification as kosher, halal and organic.

DHA in krill

Krill are tiny shrimp-like crustaceans found in the Antarctic Ocean. Krill oil contains long-chain polyunsaturated fats of the omega-3 family, EPA and docosahexaenoic acid. The great advantage of krill oil is that both these omega-3 fats come attached to phospholipids, mostly phosphatidylcholine. This structural difference of the attachment makes their absorption and utilization more efficient. In this aspect krill oil is more preferred supplement of docosahexaenoic acid than fish oil.

Related topics in Nutrition, Deficiency & Diseases:
Eicosapentaenoic acid (EPA).
Arachidonic acid (ARA).
Rickets symptoms.
Pellagra symptoms.
Osteomalacia symptoms.
Scurvy symptoms.
Beriberi symptoms.

Image source: http://en.wikipedia.org/wiki/File:DHA_numbers.svg
Image author: Timlev37
Image license: public domain

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Docosahexaenoic acid - DHA