Docosahexaenoic acid/ja: Difference between revisions

'''ドコサヘキサエン酸'''（'''DHA'''）は、ヒトの[[brain/ja|脳]]、[[cerebral cortex/ja|大脳皮質]]、[[skin/ja|皮膚]]、[[retina/ja|網膜]]の主要な構造成分である[[omega-3 fatty acid/ja|オメガ3脂肪酸]]である。22:6(n-3)'''という[[nomenclature of fatty acids/ja|脂肪酸表記法]]が与えられている。DHAは[[α-Linolenic acid/ja|α-リノレン酸]]から合成することもできるし、母乳（母乳）、脂肪分の多い魚、魚油、藻類油から直接摂取することもできる。DHA（例えば、サケ、ニシン、サバ、イワシなどの脂肪魚から）の摂取は、認知を含む多くの生理学的利益に寄与する。脳の神経細胞の主要な構造成分であるDHAの機能は、神経細胞の伝導をサポートし、神経細胞膜タンパク質（受容体や酵素など）の最適な機能を可能にすることである。

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=== Mammals ===

In humans, DHA is either obtained from the diet or may be converted in small amounts from [[eicosapentaenoic acid]] (EPA, 20:5, ω-3). With the identification of [[FADS2]] as a human Δ4-desaturase in 2015, it is now known that humans also follow the whole "aerobic eukaryote" pathway, involving Δ5-elongation to DPA and Δ4-desaturation to DHA.

A "Sprecher's shunt" hypothesis, proposed in 1991, postulates that EPA is twice elongated to 24:5 ω-3, then desaturated to 24:6 ω-3 (via [[delta 6 desaturase]]) in the mitochondria, then shortened to DHA (22:6 ω-3) via [[beta oxidation]] in the [[peroxisome]]. The hypothesis became accepted for a while because scientists have (until 2015) long tried and failed to find a Δ4-desaturase in mammals. However, the shunt model does not match clinical data, specifically as patients with beta oxidation defects do not display issues in DHA synthesis. With the identification of a Δ4-desaturase, it is considered outdated.

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=== Anaerobic pathway ===

Marine bacteria and the microalgae ''[[Schizochytrium]]'' use an anerobic [[polyketide synthase]] pathway to synthesize DHA.

==Metabolism==

DHA can be metabolized into DHA-derived [[specialized pro-resolving mediators]] (SPMs), DHA epoxides, electrophilic oxo-derivatives (EFOX) of DHA, neuroprostanes, ethanolamines, acylglycerols, docosahexaenoyl amides of amino acids or neurotransmitters, and branched DHA esters of hydroxy fatty acids, among others.

The enzyme [[CYP2C9]] metabolizes DHA to [[epoxydocosapentaenoic acid]]s (EDPs; primarily 19,20-epoxy-eicosapentaenoic acid isomers [i.e. 10,11-EDPs]).

==Potential health effects==

{{See also|Omega-3 fatty acid#Health effects}}

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===Cardiovascular===

Though mixed and plagued by methodological inconsistencies, there is now convincing evidence from ecological, RCTs, meta-analyses and animal trials show a benefit for omega-3 dietary intake for cardiovascular health. Of the n-3 FAs, DHA has been argued to be the most beneficial due to its preferential uptake in the myocardium, its strongly anti-inflammatory activity and its metabolism toward neuroprotectins and resolvins, the latter of which directly contribute to cardiac function.

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===Pregnancy and lactation===

Foods high in omega-3 fatty acids may be recommended to women who want to become pregnant or when nursing. A working group from the International Society for the Study of Fatty Acids and Lipids recommended 300&nbsp;mg/day of DHA for pregnant and lactating women, whereas the average consumption was between 45&nbsp;mg and 115&nbsp;mg per day of the women in the study, similar to a Canadian study.

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===Brain and visual functions===

A major structural component of the mammalian central nervous system, DHA is the most abundant omega−3 fatty acid in the brain and retina. Brain and retinal function rely on dietary intake of DHA to support a broad range of [[cell membrane]] and [[cell signaling]] properties, particularly in [[grey matter]] and retinal [[photoreceptor cell]] outer segments, which are rich in membranes.

A [[systematic review]] found that DHA had no significant benefits in improving visual field in individuals with [[retinitis pigmentosa]]. Animal research shows effect of oral intake of [[reinforced lipids|deuterium-reinforced]] DHA (D-DHA) for prevention of [[macular degeneration]].

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=== Asthma ===

==Nutrition==

[[File:DHA pills.jpg|thumb|Algae-based DHA supplements]]

Ordinary types of cooked [[salmon]] contain 500–1500&nbsp;mg DHA and 300–1000&nbsp;mg EPA per 100&nbsp;grams. Additional rich seafood sources of DHA include [[caviar]] (3400&nbsp;mg per 100 grams), [[anchovy|anchovies]] (1292&nbsp;mg per 100 grams), [[mackerel]] (1195&nbsp;mg per 100 grams), and cooked [[herring]] (1105&nbsp;mg per 100 grams).

[[Brain as food|Brains from mammals taken as food]] are also a good direct source. Beef brain, for example, contains approximately 855&nbsp;mg of DHA per 100 grams in a serving. While DHA may be the primary fatty acid found in certain specialized tissues, these tissues, aside from the brain, are typically small in size, such as the seminiferous tubules and the retina. As a result, animal-based foods, excluding the brain, generally offer minimal amounts of preformed DHA.

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===Discovery of algae-based DHA===

In the early 1980s, [[NASA]] sponsored scientific research on a plant-based food source that could generate oxygen and nutrition on long-duration [[space flight]]s. Certain species of marine [[algae]] produced rich nutrients, leading to the development of an algae-based, vegetable-like oil that contains two polyunsaturated fatty acids, DHA and [[arachidonic acid]].

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===Use as a food additive===

DHA is widely used as a [[food supplement]]. It was first used primarily in infant formulas. In 2019, the US Food and Drug Administration published qualified [[health claim]]s for DHA.

Some manufactured DHA is a [[vegetarian]] product extracted from algae, and it competes on the market with fish oil that contains DHA and other omega-3s such as [[Eicosapentaenoic acid|EPA]]. Both fish oil and DHA are odorless and tasteless after processing as a food additive.

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===Studies of vegetarians and vegans===

{{Main|Vegetarian nutrition#Omega-3 fatty acids}}

[[Vegetarian]] diets typically contain limited amounts of DHA, and [[vegan]] diets typically contain no DHA. In preliminary research, algae-based [[dietary supplement|supplements]] increased DHA levels. While there is little evidence of adverse health or cognitive effects due to DHA deficiency in adult vegetarians or vegans, [[breast milk]] levels remain a concern for supplying adequate DHA to the infant.

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===DHA and EPA in fish oils===

Fish oil is widely sold in [[capsule (pharmacy)|capsules]] containing a mixture of omega-3 fatty acids, including EPA and DHA. [[Oxidation|Oxidized]] fish oil in supplement capsules may contain lower levels of EPA and DHA. Light, oxygen exposure, and heat can all contribute to oxidation of fish oil supplements. Buying a quality product that is kept cold in storage and then keeping it in a refrigerator can help minimize oxidation.