Docosahexaenoic Acid (DHA)
Docosahexaenoic acid (DHA) is a major component of fish oil. It is a long-chain polyunsaturated fatty acid (LCPUFA) of the n-3 or omega-3 type. DHA is an all cis polyunsaturated fatty acid containing 22 carbon atoms and 6 double bonds. DHA is a vital component of the phospholipids of human cellular membranes, especially those in the brain and retina. It is necessary for optimal neural development and visual acuity. DHA is the most abundant omega-3 fatty acid in human breast milk. DHA occurs naturally in the form of triacylglycerols (TAGs).
Docosahexaenoic (or docosahexanoic) acid (DHA), one of the omega-3 fatty acids, appears to possess beneficial influences on human visual function and may be important in the infant diet. The triple long-chain polyunsaturated fatty acid DHA is one of the least saturated fatty acids in the human body, and is highly enriched in the membrane lipids of rod photoreceptors in the human eye, but also concentrates in the brain. Docosahexaenoic acid, sometimes referred to by nutritionists as "brain oil," is one of the primary structural components of brain tissues, which are 60 percent fats. DHA's triglyceride-lowering property results from the combined effects of inhibition of lipogenesis and stimulation of fatty acid oxidation. Fatty acid oxidation of eicosapentaenoic (EPA) acid occurs mainly in the mitochondria, while DHA undergoes fatty acid oxidation in the peroxisomes. DHA is taken up by the brain in preference to other fatty acids and is incorporated into the phospholipids of the cell membranes of brain cells and the retina. DHA-containing phospholipids in the cell membranes of the neurons appear to be necessary for neurite elongation and formation of synapses. DHA-containing phospholipids in these cells are believed to be vital for cell signaling. DHA is the prominent structural fatty acid in the gray matter of the brain and retinal tissues of humans, as well as other animals.
The balance of fatty acids in various diets around the world may reflect varying risks of breast cancer. Other health attributes for high docosahexaenoic acid intake include reduced heart disease, reduced blood triglycerides, partial reversals in diabetes mellitus, attention-deficit hyperactivity disorder, depression and schizophrenia treatments, and possible delays in the onset of autoimmune disease (primarily AIDS).
Docosahexaenoic acid (DHA) is essential for the growth and functional development of the brain in infants. DHA is also required for maintenance of normal brain function in adults. The inclusion of plentiful DHA in the diet improves learning ability, whereas deficiencies of DHA are associated with deficits in learning. DHA is taken up by the brain in preference to other fatty acids. The turnover of DHA in the brain is very fast, more so than is generally realized. The visual acuity of healthy, full-term, formula-fed infants is increased when their formula includes DHA. During the last 50 years, many infants have been fed formula diets lacking DHA and other omega-3 fatty acids. DHA deficiencies are associated with foetal alcohol syndrome, attention deficit hyperactivity disorder, cystic fibrosis, phenylketonuria, unipolar depression, aggressive hostility, and adrenoleukodystrophy. Decreases in DHA in the brain are associated with cognitive decline during aging and with onset of sporadic Alzheimer disease. The leading cause of death in western nations is cardiovascular disease. Epidemiological studies have shown a strong correlation between fish consumption and reduction in sudden death from myocardial infarction. The reduction is approximately 50% with 200 mg day(-1)of DHA from fish. DHA is the active component in fish. Not only does fish oil reduce triglycerides in the blood and decrease thrombosis, but it also prevents cardiac arrhythmias. The association of DHA deficiency with depression is the reason for the robust positive correlation between depression and myocardial infarction. Patients with cardiovascular disease or Type II diabetes are often advised to adopt a low-fat diet with a high proportion of carbohydrate. A study with women shows that this type of diet increases plasma triglycerides and the severity of Type II diabetes and coronary heart disease. DHA is present in fatty fish (salmon, tuna, mackerel) and mother's milk. DHA is present at low levels in meat and eggs, but is not usually present in infant formulas. EPA, another long-chain n-3 fatty acid, is also present in fatty fish. The shorter chain n-3 fatty acid, alpha-linolenic acid, is not converted very well to DHA in man. These longchain n-3 fatty acids (also known as omega-3 fatty acids) are now becoming available in some foods, especially infant formula and eggs in Europe and Japan. Fish oil decreases the proliferation of tumour cells, whereas arachidonic acid, a longchain n-6 fatty acid, increases their proliferation. These opposite effects are also seen with inflammation, particularly with rheumatoid arthritis, and with asthma. DHA has a positive effect on diseases such as hypertension, arthritis, atherosclerosis, depression, adult-onset diabetes mellitus, myocardial infarction, thrombosis, and some cancers.