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Docosahexaenoic acid (DHA) is an omega−3 fatty acid that is an important component of the human brain, cerebral cortex, skin, and retina. It is given the fatty acid notation 22:6(n−3). [1] It can be synthesized from alpha-linolenic acid or obtained directly from maternal milk (breast milk), fatty fish, fish oil, or algae oil.
An omega−3 fatty acid is a fatty acid with multiple double bonds, where the first double bond is between the third and fourth carbon atoms from the end of the carbon atom chain. "Short-chain" omega−3 fatty acids have a chain of 18 carbon atoms or less, while "long-chain" omega−3 fatty acids have a chain of 20 or more.
Refsum disease is an autosomal recessive [5] neurological disease that results in the over-accumulation of phytanic acid in cells and tissues. It is one of several disorders named after Norwegian neurologist Sigvald Bernhard Refsum (1907–1991).
Mammals are unable to synthesize omega−3 fatty acids, but can obtain the shorter-chain omega−3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega−3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds). [2]
Deficiency in omega−3 fatty acids are very common. The average American has a dietary ratio between omega−6 fatty acids and omega−3 fatty acids of 20:1. When the two EFAs were discovered in 1923, they were designated "vitamin F", but in 1929, research on rats showed that the two EFAs are better classified as fats rather than vitamins. [8]
Intake of large doses (2.0 to 4.0 g/day) of long-chain omega−3 fatty acids as prescription drugs or dietary supplements are generally required to achieve significant (> 15%) lowering of triglycerides, and at those doses the effects can be significant (from 20% to 35% and even up to 45% in individuals with levels greater than 500 mg/dL).
This can be caused by age, contact lens use, meibomian gland dysfunction, [7] pregnancy, Sjögren syndrome, vitamin A deficiency, omega-3 fatty acid deficiency, LASIK surgery, and certain medications such as antihistamines, some blood pressure medication, hormone replacement therapy, and antidepressants.
To illustrate the amounts of EPA and DHA in supplements, a softgel capsule containing fish oil derived from pollock might contain a total of 642 mg of total fish oil, of which 584 mg are omega−3 fatty acids, with 377 mg EPA and 158 mg DHA. 3 That same company's salmon oil softgel contains 1008 mg of total fish oil, of which 295 mg are omega ...