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|Section2= |Section3= }} Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, sperm, testicles and retina. It can be synthesized from alpha-linolenic acid or obtained directly from maternal milk or fish oil. DHA's structure is a carboxylic acid (-''oic acid'') with a 22-carbon chain (''docosa-'' is Greek for 22) and six (''hexa-'') ''cis'' double bonds (''-en-'');〔http://www.websters-online-dictionary.org/definitions/Docosahexaenoic%20Acids〕 with the first double bond located at the third carbon from the omega end.〔The omega end is the one furthest from the carboxyl group.〕 Its trivial name is cervonic acid, its systematic name is ''all-cis''-docosa-4,7,10,13,16,19-hexa-enoic acid, and its shorthand name is 22:6(n-3) in the nomenclature of fatty acids. Cold-water oceanic fish oils are rich in DHA. Most of the DHA in fish and multi-cellular organisms with access to cold-water oceanic foods originates from photosynthetic and heterotrophic microalgae, and becomes increasingly concentrated in organisms the further they are 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. Some animals with access to seafood make very little DHA through metabolism, but obtain it in the diet. However, in strict herbivores, and carnivores that do not eat seafood, DHA is manufactured internally from α-linolenic acid, a shorter omega-3 fatty acid manufactured by plants (and also occurring in animal products as obtained from plants). Limited amounts of eicosapentaenoic and docosapentaenoic acids are possible products of α-linolenic acid metabolism in young women and men, and though DHA is difficult to detect above dietary background in males compared with females, this illustrates the importance of DHA production for the developing fetus and healthy breast milk.〔Malone, J. P. (2011, August). Autistogenesis: A systems theory with evolutionary perspective. Poster presented at the American Psychological Association 119th Annual Convention, Washington, D.C. Abstract retrieved from http://forms.apa.org/convention/viewabstract.cfm?id=110999.〕 Rates of conversion are 15% higher for women, with those taking oral contraceptives demonstrating 10% higher DHA levels.〔Giltay, E.J., Gooren, L. J. G., Toorians, A. W. F. T., Katan, M. B., & Zock, P. L. (2004). Docosahexanoic acid concentrations are higher in women than in men because of estrogenic effects. ''American Journal of Clinical Nutrition'', 80(5), 1167-1174. Retrieved from http://www.ajcn.org/cgi/reprint/80/5/1167〕 Administration of testosterone or the aromatase inhibitor anastrozole, which blocks conversion of testosterone to estradiol, reduces DHA conversion.〔 DHA is a major fatty acid in sperm and brain phospholipids and in the retina. A low level of DHA is spotted in patients with retinitis pigmentosa. Below-normal levels of DHA have also been associated with Alzheimer's disease. Dietary DHA may reduce the level of blood triglycerides in humans. Nonetheless, studies of fish oil supplements, which contain DHA, have failed to support claims of preventing heart attacks or strokes. ==Central nervous system constituent== DHA is the most abundant omega-3 fatty acid in the brain and retina. DHA comprises 40% of the polyunsaturated fatty acids (PUFAs) in the brain and 60% of the PUFAs in the retina. Fifty percent of the weight of a neuron's plasma membrane is composed of DHA. DHA is richly supplied during breastfeeding, and DHA levels are high in breastmilk regardless of dietary choices. DHA 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. Phosphatidylserine (PS) controls apoptosis, and low DHA levels lower neural cell PS and increase neural cell death.〔 〕 DHA levels are reduced in the brain tissue of severely depressed patients. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「docosahexaenoic acid」の詳細全文を読む スポンサード リンク
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