Omega-3 fatty acid/ja

ω-3脂肪酸（Omega-3 fatty acids）は、オメガ3油、オメガ3脂肪酸またはn-3脂肪酸とも呼ばれ、その化学構造において末端のメチル基から3原子離れたところに二重結合が存在することを特徴とする多価不飽和脂肪酸（PUFA）である。オメガ3脂肪酸は自然界に広く分布し、動物の脂質代謝の重要な構成成分である。ヒトの生理学に関与するオメガ3脂肪酸は、α-リノレン酸（ALA）、エイコサペンタエン酸（EPA）、ドコサヘキサエン酸（DHA）の3種類である。ALAは植物に含まれ、DHAとEPAは藻類や魚類に含まれる。海藻や物プランクトンはオメガ3脂肪酸の主な供給源である。DHAとEPAは、これらの藻類を食べる魚に蓄積される。ALAを含む植物油の一般的な供給源としては、クルミ、食用種子、フラックスシード、および麻実油があり、EPAとDHAの供給源としては、魚および魚油、および藻類油がある。

哺乳類は必須オメガ3脂肪酸であるALAを合成することができず、食事を通じてのみ摂取することができる。しかし、ALAが入手可能な場合は、その炭素鎖に沿って二重結合をさらに作り（脱飽和）、それを伸ばす（伸長）ことによって、EPAとDHAを形成するためにALAを使用することができる。すなわち、ALA（炭素数18、二重結合3個）を使ってEPA（炭素数20、二重結合5個）を作り、それを使ってDHA（炭素数22、二重結合6個）を作る。加齢により、ALAから長鎖オメガ3脂肪酸を作る能力が低下する可能性がある。空気に触れる食品では、不飽和脂肪酸は酸化や腐敗を起こしやすい。

オメガ3脂肪酸の栄養補助食品摂取ががんや心血管系疾患のリスクを低減するという質の高い証拠はない。魚油サプリメントの研究では、心筋梗塞や脳卒中、あるいは血管疾患の転帰を予防するという主張を支持することはできなかった。

歴史

1929年、ジョージ・バーとミルドレッド・バーは、脂肪酸が健康に不可欠であることを発見した。食事から脂肪酸が欠乏すると、生命を脅かす欠乏症が起こる。バー夫妻は「必須脂肪酸」という言葉を生み出した。それ以来、生物の細胞膜の骨格を形成する不飽和必須脂肪酸への関心が研究者の間で高まっている。その後、1980年代以降、必須脂肪酸の健康効果に対する認識が飛躍的に高まった。

2004年9月8日、米国食品医薬品局は、EPAとDHAのオメガ3脂肪酸に「適格健康強調表示」のステータスを与え、「決定的な研究ではないが、EPAとDHA（オメガ3）脂肪酸の摂取が冠動脈性心臓病のリスクを減らす可能性があることを示している」と述べた。これは、2001年の健康リスクアドバイスレター（下記参照）を更新し、変更した。

カナダ食品検査庁は、DHAオメガ3の重要性を認識し、DHAについて次のような表示を許可している。"オメガ3脂肪酸であるDHAは、主に2歳未満の子供の脳、目、神経の正常な身体発達をサポートする"。

歴史的には、ホールフードの食事には十分な量のオメガ3が含まれていたが、オメガ3は酸化されやすいため、保存のきく加工食品への傾向が、製造された食品におけるオメガ3の欠乏につながっている。

命名法

詳細は「脂肪酸」を参照

α-リノレン酸（ALA）の化学構造。炭素数9、12、15の3つの二重結合を持つ炭素数18の鎖を持つ脂肪酸である。鎖のオメガ（ω）末端は炭素18にあり、オメガ炭素に最も近い二重結合は炭素15＝18-3から始まる。したがって、ALAはω=18のω-3脂肪酸である。

用語ω-3脂肪酸とn-3脂肪酸は有機化学の命名法に由来する。不飽和脂肪酸が命名される1つの方法は、その炭素鎖において、分子のメチル末端に最も近い二重結合の位置によって決定される。一般的な用語では、n（またはω）は分子のメチル末端の位置を表し、数n-x（またはω-x）は最も近い二重結合の位置を指す。したがって、特にω-3脂肪酸では、脂肪酸鎖のメチル末端から始まる炭素番号3の位置に二重結合がある。ほとんどの化学変化は分子のカルボキシル末端で起こるが、メチル基とそれに最も近い二重結合はほとんどの化学反応や酵素反応において変化しないので、この分類法は有用である。

n-xまたはω-xという表現では、記号はハイフン（またはダッシュ）ではなくマイナス記号であるが、そのように読まれることはない。また、記号n（またはω）は、脂肪酸の炭素鎖のカルボキシル末端から数えて、メチル末端の位置を表す。例えば、メチル末端がカルボキシル末端から18番目の位置にある18個の炭素原子を持つオメガ3脂肪酸（図を参照）では、n（またはω）は18という数を表し、n-3（またはω-3）という表記は18-3＝15という減算を表し、ここで15は鎖のカルボキシル末端から数えてメチル末端に最も近い二重結合の位置である。

nとω（オメガ）は同義語であるが、IUPACは脂肪酸の最高炭素数を特定するためにnを使用することを推奨している。とはいえ、より一般的な名称であるオメガ3脂肪酸は、一般メディアでも科学文献でも使用されている。

例

例えば、α-リノレン酸（ALA；図）は、3つの二重結合を持つ18個の炭素鎖であり、最初の二重結合は脂肪酸鎖のメチル末端から3番目の炭素に位置している。したがって、オメガ3脂肪酸である。鎖のもう一方の端、つまりカルボキシル端から数えると、3つの二重結合は炭素9、12、15に位置する。これらの3つの位置は通常、Δ9c、Δ12c、Δ15c、またはシスΔ⁹、シスΔ¹²、シスΔ¹⁵と示される、 またはcis-cis-cis-Δ^9,12,15であり、cまたはcisは二重結合がシス配置であることを意味する。

α-リノレン酸は多価不飽和（二重結合を2つ以上含む）であり、脂質番号、18:3で表される。

化学=

エイコサペンタエン酸（EPA）の化学構造

ドコサヘキサエン酸（DHA）の化学構造

オメガ3脂肪酸は複数の二重結合を持つ脂肪酸であり、最初の二重結合は炭素原子鎖の末端から3番目と4番目の炭素原子の間にある。"短鎖"オメガ3脂肪酸は18個以下の炭素原子の鎖を持ち、"長鎖"オメガ3脂肪酸は20個以上の鎖を持つ。

α-リノレン酸（18:3、n-3、ALA）、エイコサペンタエン酸（20:5、n-3、EPA）、ドコサヘキサエン酸（22:6、n-3、DHA）である。これら3つの多価不飽和は、それぞれ18、20、22個の炭素原子の炭素鎖に3、5、または6個の二重結合を持っている。ほとんどの天然脂肪酸がそうであるように、全ての二重結合はシス構成であり、言い換えれば、2つの水素原子は二重結合の同じ側にあり、二重結合はメチレン架橋（-CH
₂-）によって中断されているので、隣接する二重結合の各対の間には2つの単結合がある。

ビスアリル（二重結合の間）にある原子はフリーラジカルによって酸化されやすい。この部位の水素原子を重水素原子で置換することで、オメガ3脂肪酸は脂質過酸化やフェロプターシスから保護される。

オメガ3脂肪酸の一覧表

この表は、自然界に存在する最も一般的なオメガ3脂肪酸のいくつかの異なる名前をリストアップしたものである。

一般名	Lipid number/ja	化学名
ヘキサデカトリエン酸 (HTA)	16:3 (n−3)	all-cis-7,10,13-hexadecatrienoic acid
α-リノレン酸 (ALA)	18:3 (n−3)	all-cis-9,12,15-octadecatrienoic acid
Stearidonic acid/ja (SDA)	18:4 (n−3)	all-cis-6,9,12,15-octadecatetraenoic acid
エイコサトリエン酸 (ETE)	20:3 (n−3)	all-cis-11,14,17-eicosatrienoic acid
Eicosatetraenoic acid/ja (ETA)	20:4 (n−3)	all-cis-8,11,14,17-eicosatetraenoic acid
エイコサペンタエン酸 (EPA)	20:5 (n−3)	all-cis-5,8,11,14,17-eicosapentaenoic acid
ヘネイコサペンタエン酸 (HPA)	21:5 (n−3)	all-cis-6,9,12,15,18-heneicosapentaenoic acid
Docosapentaenoic acid/ja (DPA), クルパノドン酸	22:5 (n−3)	all-cis-7,10,13,16,19-docosapentaenoic acid
ドコサヘキサエン酸 (DHA)	22:6 (n−3)	all-cis-4,7,10,13,16,19-docosahexaenoic acid
テトラコサペンタエン酸	24:5 (n−3)	all-cis-9,12,15,18,21-tetracosapentaenoic acid
Tetracosahexaenoic acid/ja (ニシン酸)	24:6 (n−3)	all-cis-6,9,12,15,18,21-tetracosahexaenoic acid

形状

オメガ3脂肪酸は、トリグリセリドとリン脂質の2つの形態で天然に存在する。トリグリセリドでは、他の脂肪酸とともにグリセロールに結合しており、3つの脂肪酸がグリセロールに結合している。リン脂質オメガ3は、グリセロールを介してリン酸基に結合した2つの脂肪酸で構成されている。

トリグリセリドは遊離脂肪酸、またはメチルエステルやエチルエステルに変換することができ、オメガ3脂肪酸の個々のエステルを利用できる。

作用機序

必須」脂肪酸は、幼児や動物の正常な成長に不可欠であることを研究者が発見したことから、その名が付けられた。オメガ3脂肪酸のDHAはドコサヘキサエン酸とも呼ばれ、ヒトの脳に多く存在する。DHAは脱飽和プロセスによって生成されるが、ヒトはω₆とω₃の位置に二重結合を挿入する働きをする脱飽和酵素を欠いている。したがって、ω₆およびω₃多価不飽和脂肪酸は合成できず、必須脂肪酸と呼ばれるのが適切であり、食事から摂取しなければならない。

1964年、羊の組織に存在する酵素が、オメガ6アラキドン酸を炎症化物質であるプロスタグランジンに変換することが発見された。E₂は外傷や感染組織の免疫反応に関与している。1979年までに、トロンボキサン、プロスタサイクリン、ロイコトリエンを含むエイコサノイドがさらに同定された。エイコサノイドは通常、体内での活性期間が短く、脂肪酸からの合成に始まり、酵素による代謝で終わる。合成速度が代謝速度を上回ると、過剰なエイコサノイドが有害な影響を及ぼす可能性がある。オメガ-3脂肪酸とオメガ-6脂肪酸の両方が存在する場合、それらは変換されるために「競合」するので、長鎖オメガ-3：オメガ-6脂肪酸の比率は、生成されるエイコサノイドの種類に直接影響する。

相互変換

ALAからEPAとDHAへの変換効率

ヒトは短鎖オメガ3脂肪酸を5％以下の効率で長鎖型（EPA、DHA）に変換できる。オメガ3の変換効率は男性よりも女性の方が高いが、あまり研究されていない。女性の血漿リン脂質に見られるALAとDHAの値が高いのは、デサチュラーゼ、特にδ-6-デサチュラーゼの活性が高いためかもしれない。

これらの変換は、リノール酸から誘導される必須の密接に関連した化学類似体であるオメガ6脂肪酸と競合的に起こる。両者とも炎症制御タンパク質を合成するために、同じデサチュラーゼとエロンガーゼタンパク質を利用している。オメガ3系とオメガ6系をバランスよく摂取することは、個人の健康にとって重要である。タンパク質が両方の経路を十分に合成できるようにするためには、1：1のバランスのとれた摂取比率が理想的だと考えられていたが、最近の研究では、これには賛否両論がある。

ヒトにおけるALAからEPA、さらにDHAへの変換は限定的であると報告されているが、個人差がある。女性の方が男性よりもALAからDHAへの変換効率が高いが、これは食事性ALAがβ酸化に利用される割合が低いためと推定される。ある予備研究では、食事性リノール酸の摂取量を減らすことでEPAを増加させることができ、食事性ALAの摂取量を増やすことでDHAを増加させることができることが示された。

オメガ6とオメガ3の比率

詳細は「Essential fatty acid interactions/ja」を参照

ヒトの食生活はここ数世紀で急速に変化し、その結果、オメガ3に比べてオメガ6の摂取量が増加したと報告されている。新石器時代の農業革命のような、オメガ3とオメガ6の比率が1:1であった時代からヒトの食事が急速に進化したことは、オメガ3とオメガ6の比率が1:1であった時代のような、オメガ3とオメガ6の比率が1:1であった時代に適応した生物学的プロファイルを持つには、ヒトの進化が早すぎたと考えられる。これが、現代の食生活が多くの炎症性疾患と関連している理由であると一般的に考えられている。オメガ3系多価不飽和脂肪酸はヒトの心臓病予防に有益かもしれないが、オメガ6系多価不飽和脂肪酸のレベル（つまり比率）は問題ではない。

オメガ6脂肪酸もオメガ3脂肪酸も必須脂肪酸であり、ヒトは食事から摂取しなければならない。オメガ6脂肪酸とオメガ3脂肪酸の炭素数18の多価不飽和脂肪酸は、同じ代謝酵素を取り合うため、摂取する脂肪酸のオメガ6：オメガ3の比率は、特にプロスタグランジン、ロイコトリエン、トロンボキサンなどを含む、身体の炎症と恒常性維持過程に深く関与するホルモン群であるエイコサノイドの比率と産生速度に大きな影響を及ぼす。この比率を変えることで、身体の代謝状態や炎症状態を変化させることができる。

オメガ6の代謝産物（特にアラキドン酸）は、オメガ3の代謝産物よりも炎症を起こしやすい。しかし、心臓の健康という点では、オメガ6脂肪酸は考えられているよりも害が少ない。6つの無作為化試験のメタ分析によると、飽和脂肪をオメガ6脂肪に置き換えると、冠動脈イベントのリスクが24％減少した。

オメガ6とオメガ3の健康的な比率が必要である。ある著者によると、健康的な比率は1：1から1：4である。他の著者は、4：1（オメガ6がオメガ3の4倍）がすでに健康的であると考えている。

一般的な西洋の食生活では、オメガ6脂肪酸とオメガ3脂肪酸の比率は10：1から30：1（つまり、オメガ3脂肪酸よりもオメガ6脂肪酸の方が劇的に多い）である。一般的な植物油に含まれるオメガ6系脂肪酸とオメガ3系脂肪酸の比率は以下の通りである： キャノーラ 2:1、 麻 2-3:1、大豆 7:1、オリーブ 3-13:1、ひまわり（オメガ3は含まない）、亜麻 1：3、綿実油（オメガ3なし）、ピーナッツ（オメガ3なし）、グレープシードオイル（オメガ3なし）、コーン油である。46:1.

生化学

輸送体

リゾホスファチジルコリンの形をしたDHAは、血液脳関門の内皮にのみ発現する膜輸送タンパク質、MFSD2Aによって脳内に輸送される。

食事源

3オンス（85g）あたりオメガ3グラム

一般名	グラム オメガ3
Herring/ja, sardines/ja	1.3–2
Mackerel/ja: サワラ/大西洋/太平洋	1.1–1.7
Salmon/ja	1.1–1.9
Halibut/ja	0.60–1.12
Tuna/ja	0.21–1.1
Swordfish/ja	0.97
ムール貝	0.95
Tilefish/ja	0.9
ツナ（缶詰、ライト）	0.17–0.24
Pollock/ja	0.45
Cod/ja	0.15–0.24
Catfish/ja	0.22–0.3
Flounder/ja	0.48
Grouper/ja	0.23
Mahi mahi/ja	0.13
マダイ	0.29
Shark/ja	0.83
King mackerel/ja	0.36
ホキ（ブルー・グレナディア）	0.41
マンボウ	0.40
ブルー・アイ・コッド	0.31
Sydney rock oysters/ja	0.30
ツナ、缶詰	0.23
タイ	0.22
卵、レギュラー大	0.109
Strawberry/jaあるいはKiwifruit/ja	0.10–0.20
Broccoli/ja	0.10–0.20
バラマンディ、海水魚	0.100
Giant tiger prawn/ja	0.100
赤身の肉	0.031
ターキー	0.030
ミルク、レギュラー	0.00

食事摂取基準

米国では、医学研究所が食事摂取基準の体系を発表しており、個々の栄養素については推奨食事摂取量（RDA）、脂肪など特定の栄養素群については許容可能大栄養素分布範囲（AMDR）が含まれている。RDAを決定するのに十分な証拠がない場合、研究所は代わりに十分な摂取量（AI）を公表することがある。α-リノレン酸のAIは男性で1.6 グラム/日、女性で1.1 グラム/日であり、AMDRは総エネルギーの0.6%から1.2%である。EPAとDHAの生理的効力はALAよりもはるかに大きいため、すべてのオメガ3脂肪酸について1つのAMDRを推定することはできない。AMDRの約10％は、EPAおよび/またはDHAとして消費することができる。医学研究所は、EPA、DHAまたはその組み合わせについてRDAまたはAIを設定していないため、1日当たりの摂取量（DVはRDAから派生）、1食あたりこれらの脂肪酸のDVパーセンテージを提供する食品やサプリメントの表示、および食品やサプリメントに優れた供給源、または "High in... "と表示することはない。安全性に関しては、2005年の時点では、オメガ3脂肪酸の耐容上限量を設定するには十分な証拠がなかったが、FDAは、成人はDHAとEPAを合わせて1日あたり合計3 gまでなら安全に摂取できるが、栄養補助食品からの摂取は2 gまでと勧告している。

欧州委員会は、妊娠中および授乳期の食事脂肪摂取に関する勧告を作成するワーキンググループを後援した。2008年、作業部会は以下のようなコンセンサス勧告を発表した：

• "pregnant and lactating women should aim to achieve an average dietary intake of at least 200 mg DHA/day"
• "women of childbearing age should aim to consume one to two portions of sea fish per week, including oily fish"
• "intake of the DHA precursor, α-linolenic acid, is far less effective with regard to DHA deposition in fetal brain than preformed DHA"

However, the seafood supply to meet these recommendations is currently too low in most European countries and if met would be unsustainable.

In the EU, the EFSA publishes the Dietary Reference Values (DRVs), recommending Adequate Intake values for EPA+DHA and DHA:

Dietary Reference Values (DRVs) for EPA+DHA and DHA

Age group (years)	EPA+DHA (mg/day)	DHA (mg/day)
7–11 months		100
1		100
2-3	250
4-6	250
7-10	250
11-14	250
15-17	250
≥18	250
Pregnancy	250	+ 100—200
Lactation	250	+ 100—200

^1 AI, Adequate Intake

^2 i.e. the second half of the first year of life (from the beginning of the 7th month to the 1st birthday)

^3 in addition to combined intakes of EPA and DHA of 250 mg/day

The American Heart Association (AHA) has made recommendations for EPA and DHA due to their cardiovascular benefits: individuals with no history of coronary heart disease or myocardial infarction should consume oily fish two times per week; and "Treatment is reasonable" for those having been diagnosed with coronary heart disease. For the latter the AHA does not recommend a specific amount of EPA + DHA, although it notes that most trials were at or close to 1000 mg/day. The benefit appears to be on the order of a 9% decrease in relative risk. The European Food Safety Authority (EFSA) approved a claim "EPA and DHA contributes to the normal function of the heart" for products that contain at least 250 mg EPA + DHA. The report did not address the issue of people with pre-existing heart disease. The World Health Organization recommends regular fish consumption (1-2 servings per week, equivalent to 200 to 500 mg/day EPA + DHA) as protective against coronary heart disease and ischaemic stroke.

Contamination

Heavy metal poisoning from consuming fish oil supplements is highly unlikely, because heavy metals (mercury, lead, nickel, arsenic, and cadmium) selectively bind with protein in the fish flesh rather than accumulate in the oil.

However, other contaminants (PCBs, furans, dioxins, and PBDEs) might be found, especially in less-refined fish oil supplements.

Throughout their history, the Council for Responsible Nutrition and the World Health Organization have published acceptability standards regarding contaminants in fish oil. The most stringent current standard is the International Fish Oils Standard. Fish oils that are molecularly distilled under vacuum typically make this highest-grade; levels of contaminants are stated in parts per billion per trillion.

Rancidity

A 2022 study found that a number of products on the market used oxidised oils, with the rancidity often masked by flavourings. Another study in 2015 found that an average of 20% of products had excess oxidation. Whether rancid fish oil is harmful remains unclear. Some studies show that highly oxidised fish oil can have a negative impact on cholesterol levels. Animal testing showed that high doses have toxic effects. Furthermore, rancid oil is likely to be less effective than fresh fish oil.

Fish

The most widely available dietary source of EPA and DHA is oily fish, such as salmon, herring, mackerel, anchovies, and sardines. Oils from these fishes have around seven times as much omega−3 as omega−6. Other oily fish, such as tuna, also contain n-3 in somewhat lesser amounts. Although fish are a dietary source of omega−3 fatty acids, fish do not synthesize omega−3 fatty acids, but rather obtain them via their food supply, including algae or plankton.

In order for farmed marine fish to have amounts of EPA and DHA comparable to those of wild-caught fish, their feed must be supplemented with EPA and DHA, most commonly in the form of fish oil. For this reason, 81% of the global fish oil supply in 2009 was consumed by aquaculture. By 2019, two alternative sources of EPA and DHA for fish have been partially commercialized: genetically-modified canola oil and Schizochytrium algal oil.

Fish oil

See also: Fish oil and Cod liver oil

Fish oil capsules

Marine and freshwater fish oil vary in content of arachidonic acid, EPA and DHA. They also differ in their effects on organ lipids.

Not all forms of fish oil may be equally digestible. Of four studies that compare bioavailability of the glyceryl ester form of fish oil vs. the ethyl ester form, two have concluded the natural glyceryl ester form is better, and the other two studies did not find a significant difference. No studies have shown the ethyl ester form to be superior, although it is cheaper to manufacture.

Krill

Krill oil is a source of omega−3 fatty acids. The effect of krill oil, at a lower dose of EPA + DHA (62.8%), was demonstrated to be similar to that of fish oil on blood lipid levels and markers of inflammation in healthy humans. While not an endangered species, krill are a mainstay of the diets of many ocean-based species including whales, causing environmental and scientific concerns about their sustainability. Preliminary studies appear to indicate that the DHA and EPA omega−3 fatty acids found in krill oil may be more bio-available than in fish oil. Additionally, krill oil contains astaxanthin, a marine-source keto-carotenoid antioxidant that may act synergistically with EPA and DHA.

Plant sources

See also: Algal oil

Chia is grown commercially for its seeds rich in ALA

Flax seeds contain linseed oil which has high ALA content

Capsules of omega-3 oil derived from marine algae (Schizochytrium sp.), 96.3% of total content

Table 1. ALA content as the percentage of the seed oil.

Common name	Alternative name	Linnaean name	% ALA
kiwifruit (fruit)	Chinese gooseberry	Actinidia deliciosa	63
perilla	shiso	Perilla frutescens	61
chia	chia sage	Salvia hispanica	58
linseed	flax	Linum usitatissimum	53 – 59
lingonberry	cowberry	Vaccinium vitis-idaea	49
fig	common fig	Ficus carica	47.7
camelina	gold-of-pleasure	Camelina sativa	36
purslane	portulaca	Portulaca oleracea	35
black raspberry		Rubus occidentalis	33
hempseed		Cannabis sativa	19
canola	rapeseed	mostly Brassica napus	9 – 11

Table 2. ALA content as the percentage of the whole food.

Common name	Linnaean name	% ALA
linseed	Linum usitatissimum	18.1
hempseed	Cannabis sativa	8.7
butternut	Juglans cinerea	8.7
Persian walnut	Juglans regia	6.3
pecan	Carya illinoinensis	0.6
hazelnut	Corylus avellana	0.1

Linseed (or flaxseed) (Linum usitatissimum) and its oil are perhaps the most widely available botanical source of the omega−3 fatty acid ALA. Flaxseed oil consists of approximately 55% ALA, which makes it six times richer than most fish oils in omega−3 fatty acids. A portion of this is converted by the body to EPA and DHA, though the actual converted percentage may differ between men and women.

The longer-chain EPA and DHA are only naturally made by marine algae and phytoplankton. The microalgae Crypthecodinium cohnii and Schizochytrium are rich sources of DHA, but not EPA, and can be produced commercially in bioreactors for use as food additives. Oil from brown algae (kelp) is a source of EPA. The alga Nannochloropsis also has high levels of EPA.

Some transgenic initiatives have transferred the ability to make EPA and DHA into existing high-yielding crop species of land plants:

• Camelina sativa: In 2013, Rothamsted Research reported two genetically modified forms of this plant. Oil from the seeds of this plant contained on average 15% ALA, 11% EPA, and 8% DHA in one development and 11% ALA and 24% EPA in another.
• Canola: In 2011, CSIRO, GRDC, and Nufarm developed a version of canola that produces DHA in seeds; the oil contains 10% DHA and almost no EPA. In 2018, it was approved as an animal feed additive in Australia. In 2021, the US FDA acknowledged it as a New Dietary Ingredient for humans. Separately, Cargill has commercialized a different strain of canola that produces EPA and DHA for fish feed. The oil contains 8.1% EPA and 0.8% DHA.

Eggs

Eggs produced by hens fed a diet of greens and insects contain higher levels of omega−3 fatty acids than those produced by chickens fed corn or soybeans. In addition to feeding chickens insects and greens, fish oils may be added to their diets to increase the omega−3 fatty acid concentrations in eggs.

The addition of flax and canola seeds, both good sources of alpha-linolenic acid, to the diets of laying chickens, increases the omega−3 content of the eggs, predominantly DHA. However, this enrichment could lead to an increment of lipid oxidation in the eggs if the seeds are used in higher doses, without using an appropriate antioxidant.

The addition of green algae or seaweed to the diets boosts the content of DHA and EPA, which are the forms of omega−3 approved by the FDA for medical claims. A common consumer complaint is "Omega−3 eggs can sometimes have a fishy taste if the hens are fed marine oils".

Meat

Omega−3 fatty acids are formed in the chloroplasts of green leaves and algae. While seaweeds and algae are the sources of omega−3 fatty acids present in fish, grass is the source of omega−3 fatty acids present in grass-fed animals. When cattle are taken off omega−3 fatty acid-rich grass and shipped to a feedlot to be fattened on omega−3 fatty acid deficient grain, they begin losing their store of this beneficial fat. Each day that an animal spends in the feedlot, the amount of omega−3 fatty acids in its meat is diminished.

The omega−6:omega−3 ratio of grass-fed beef is about 2:1, making it a more useful source of omega−3 than grain-fed beef, which usually has a ratio of 4:1.

In a 2009 joint study by the USDA and researchers at Clemson University in South Carolina, grass-fed beef was compared with grain-finished beef. The researchers found that grass-finished beef is higher in moisture content, 42.5% lower total lipid content, 54% lower in total fatty acids, 54% higher in beta-carotene, 288% higher in vitamin E (alpha-tocopherol), higher in the B-vitamins thiamin and riboflavin, higher in the minerals calcium, magnesium, and potassium, 193% higher in total omega−3s, 117% higher in CLA (cis-9, trans-11 octadecenoic acid, a conjugated linoleic acid, which is a potential cancer fighter), 90% higher in vaccenic acid (which can be transformed into CLA), lower in the saturated fats, and has a healthier ratio of omega−6 to omega−3 fatty acids (1.65 vs 4.84). Protein and cholesterol content were equal.

The omega−3 content of chicken meat may be enhanced by increasing the animals' dietary intake of grains high in omega−3, such as flax, chia, and canola.

Kangaroo meat is also a source of omega−3, with fillet and steak containing 74 mg per 100 g of raw meat.

Seal oil

Seal oil is a source of EPA, DPA, and DHA, and is commonly used in Arctic regions. According to Health Canada, it helps to support the development of the brain, eyes, and nerves in children up to 12 years of age. Like all seal products, it is not allowed to be imported into the European Union.

A Canadian company, FeelGood Natural Health, pleaded guilty in 2023 to illegally selling seal oil capsules to American consumers. The company sold over 900 bottles of the capsules, worth over $10,000. Seal oil is made from the blubber of dead seals, and is illegal to sell in the United States under the Marine Mammal Protection Act. The global population of harp seals stands at around 7 million, and they have been hunted in Canada for thousands of years. FeelGood was sentenced to pay a fine of $20,000 and three years of probation.

Other sources

A trend in the early 21st century was to fortify food with omega−3 fatty acids.

Health effects of omega-3 supplementation

The association between supplementation and a lower risk of all-cause mortality is inconclusive.

Cancer

There is insufficient evidence that supplementation with omega−3 fatty acids has an effect on different cancers. Omega-3 supplements do not improve body weight, muscle maintenance or quality of life in cancer patients.

Cardiovascular disease

Moderate and high quality evidence from a 2020 review showed that EPA and DHA, such as that found in omega−3 polyunsaturated fatty acid supplements, does not appear to improve mortality or cardiovascular health. There is weak evidence indicating that α-linolenic acid may be associated with a small reduction in the risk of a cardiovascular event or the risk of arrhythmia.

A 2018 meta-analysis found no support that daily intake of one gram of omega−3 fatty acid in individuals with a history of coronary heart disease prevents fatal coronary heart disease, nonfatal myocardial infarction or any other vascular event. However, omega−3 fatty acid supplementation greater than one gram daily for at least a year may be protective against cardiac death, sudden death, and myocardial infarction in people who have a history of cardiovascular disease. No protective effect against the development of stroke or all-cause mortality was seen in this population. A 2021 meta-analysis found that supplementation was associated with a reduced risk of myocardial infarction and coronary heart disease.

Fish oil supplementation has not been shown to benefit revascularization or abnormal heart rhythms and has no effect on heart failure hospital admission rates. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes. In the EU, a review by the European Medicines Agency of omega−3 fatty acid medicines containing a combination of an ethyl ester of eicosapentaenoic acid and docosahexaenoic acid at a dose of 1 g per day concluded that these medicines are not effective in secondary prevention of heart problems in people who have had a myocardial infarction.

Evidence suggests that omega−3 fatty acids modestly lower blood pressure (systolic and diastolic) in people with hypertension and in people with normal blood pressure. Omega−3 fatty acids can also reduce heart rate, an emerging risk factor. Some evidence suggests that people with certain circulatory problems, such as varicose veins, may benefit from the consumption of EPA and DHA, which may stimulate blood circulation and increase the breakdown of fibrin, a protein involved in blood clotting and scar formation. Omega−3 fatty acids reduce blood triglyceride levels, but do not significantly change the level of LDL cholesterol or HDL cholesterol. The American Heart Association position (2011) is that borderline elevated triglycerides, defined as 150–199 mg/dL, can be lowered by 0.5–1.0 grams of EPA and DHA per day; high triglycerides 200–499 mg/dL benefit from 1–2 g/day; and >500 mg/dL be treated under a physician's supervision with 2–4 g/day using a prescription product. In this population, omega−3 fatty acid supplementation decreases the risk of heart disease by about 25%.

A 2019 review found that omega-3 fatty acid supplements make little or no difference to cardiovascular mortality and that people with myocardial infarction have no benefit in taking the supplements. A 2021 review found that omega-3 supplementation did not affect cardiovascular disease outcomes.

A 2021 review concluded that use of omega-3 supplements was associated with an increased risk of atrial fibrillation in people having high blood triglycerides. A meta-analysis showed that use of marine omega-3 supplementation was associated with an increased risk of atrial fibrillation, with the risk appearing to increase for doses greater than one gram per day.

Chronic kidney disease

In people with chronic kidney disease (CKD) who require hemodialysis, there is a risk that vascular blockage due to clotting, may prevent dialysis therapy from being possible. Omega-3 fatty acids contribute to the production of eicosanoid molecules that reduce clotting. However, a Cochrane review in 2018 did not find clear evidence that omega-3 supplementation has any impact on the prevention of vascular blockage in people with CKD. There was also moderate certainty that supplementation did not prevent hospitalisation or death within a 12-month period.

Stroke

A 2022 Cochrane review of controlled trials did not find clear evidence that marine-derived omega-3 supplementation improves cognitive and physical recovery or social, and emotional wellbeing following stroke diagnosis, nor prevents stroke recurrence and mortality. In this review, mood appeared to worsen slightly among those receiving 3g fish oil supplementation for 12 weeks; psychometric scores changed by 1.41 (0.07 to 2.75) points less than those receiving palm and soy oil. However, this represented only a single small study and was not observed in a study lasting more than 3 months. Overall, the review was limited by the low number of high-quality evidence available.

Inflammation

A 2013 systematic review found tentative evidence of benefit for lowering inflammation levels in healthy adults and in people with one or more biomarkers of metabolic syndrome. Consumption of omega−3 fatty acids from marine sources lowers blood markers of inflammation such as C-reactive protein, interleukin 6, and TNF alpha.

For rheumatoid arthritis, one systematic review found consistent but modest evidence for the effect of marine n−3 PUFAs on symptoms such as "joint swelling and pain, duration of morning stiffness, global assessments of pain and disease activity" as well as the use of non-steroidal anti-inflammatory drugs. The American College of Rheumatology has stated that there may be modest benefit from the use of fish oils, but that it may take months for effects to be seen, and cautions for possible gastrointestinal side effects and the possibility of the supplements containing mercury or vitamin A at toxic levels. The National Center for Complementary and Integrative Health has concluded that "supplements containing omega−3 fatty acids ... may help relieve rheumatoid arthritis symptoms" but warns that such supplements "may interact with drugs that affect blood clotting".

Developmental disabilities

One meta-analysis concluded that omega−3 fatty acid supplementation demonstrated a modest effect for improving ADHD symptoms. A Cochrane review of PUFA (not necessarily omega−3) supplementation found "there is little evidence that PUFA supplementation provides any benefit for the symptoms of ADHD in children and adolescents", while a different review found "insufficient evidence to draw any conclusion about the use of PUFAs for children with specific learning disorders". Another review concluded that the evidence is inconclusive for the use of omega−3 fatty acids in behavior and non-neurodegenerative neuropsychiatric disorders such as ADHD and depression.

A 2015 meta-analysis of the effect of omega−3 supplementation during pregnancy did not demonstrate a decrease in the rate of preterm birth or improve outcomes in women with singleton pregnancies with no prior preterm births. A 2018 Cochrane systematic review with moderate to high quality of evidence suggested that omega−3 fatty acids may reduce risk of perinatal death, risk of low body weight babies; and possibly mildly increased LGA babies.

A 2021 umbrella review with moderate to high quality of evidence suggested that "omega-3 supplementation during pregnancy can exert favorable effects against pre-eclampsia, low-birth weight, pre-term delivery, and post-partum depression, and can improve anthropometric measures, immune system, and visual activity in infants and cardiometabolic risk factors in pregnant mothers."

Mental health

Omega-3 supplementation has not been shown to significantly affect symptoms of anxiety, major depressive disorder or schizophrenia. A 2021 Cochrane review concluded that there is not "sufficient high‐certainty evidence to determine the effects of n‐3PUFAs as a treatment for MDD". Omega−3 fatty acids have also been investigated as an add-on for the treatment of depression associated with bipolar disorder although there is limited data available. Two reviews have suggested that omega-3 fatty acid supplementation significantly improves depressive symptoms in perinatal women.

A 2015 study concluded that there are multiple factors responsible for depression and deficiency of omega 3 fatty acids can be one of them. It further stated that only those patients who have depression due to insufficient omega-3 fatty acids can respond well to the omega 3 supplements while others are unlikely to get any positive effects. Meta-analysis suggest that supplements with higher concentration of EPA than DHA are more likely to act as anti-depressants.

In contrast to dietary supplementation studies, there is significant difficulty in interpreting the literature regarding dietary intake of omega−3 fatty acids (e.g. from fish) due to participant recall and systematic differences in diets. There is also controversy as to the efficacy of omega−3, with many meta-analysis papers finding heterogeneity among results which can be explained mostly by publication bias. A significant correlation between shorter treatment trials was associated with increased omega−3 efficacy for treating depressed symptoms further implicating bias in publication.

Cognitive aging

A 2016 Cochrane review found no convincing evidence for the use of omega‐3 PUFA supplements in treatment of Alzheimer's disease or dementia. There is preliminary evidence of effect on mild cognitive problems, but none supporting an effect in healthy people or those with dementia. A 2020 review suggested that omega 3 supplementation has no effect on global cognitive function but has a mild benefit in improving memory in non-demented adults.

A 2022 review found promising evidence for prevention of cognitive decline in people who regularly eat long-chain omega 3 rich foods. Conversely, clinical trials with participants already diagnosed with Alzheimer's show no effect. A 2020 review concluded that long-chain omega-3 supplements do not deter cognitive decline in older adults.

Brain and visual functions

Brain function and vision rely on dietary intake of DHA to support a broad range of cell membrane properties, particularly in grey matter, which is rich in membranes. A major structural component of the mammalian brain, DHA is the most abundant omega−3 fatty acid in the brain. Omega 3 PUFA supplementation has no effect on macular degeneration or development of visual loss.

Atopic diseases

Results of studies investigating the role of LCPUFA supplementation and LCPUFA status in the prevention and therapy of atopic diseases (allergic rhinoconjunctivitis, atopic dermatitis, and allergic asthma) are controversial; therefore, 2013年現在 it could not be stated either that the nutritional intake of n−3 fatty acids has a clear preventive or therapeutic role, or that the intake of n-6 fatty acids has a promoting role in the context of atopic diseases.

Phenylketonuria

People with PKU often have low intake of omega−3 fatty acids, because nutrients rich in omega−3 fatty acids are excluded from their diet due to high protein content.

Asthma

As of 2015, there was no evidence that taking omega−3 supplements can prevent asthma attacks in children.

糖尿病

2019年のレビューでは、オメガ3サプリメントは2型糖尿病の予防と治療に効果がないことがわかった。2021年のメタアナリシスでは、オメガ3のサプリメントは糖尿病のバイオマーカー、例えば空腹時血糖値やインスリン抵抗性にプラスの効果があることがわかった。

こちらも参照

• オメガ-3脂肪酸エチルエステル
• Essential fatty acid interactions/ja
• Essential nutrients/ja
• Inflammation/ja
• Olive oil regulation and adulteration/ja
• Omega-6 fatty acid/ja
• Omega-7 fatty acid/ja
• Omega-9 fatty acid/ja
• Ratio of fatty acids in different foods/ja
• Reinforced lipids/ja

さらに読む

• Allport S (September 2006). The Queen of Fats: Why Omega−3s Were Removed from the Western Diet and What We Can Do to Replace Them. University of California Press. ISBN 978-0-520-24282-1. OCLC 801139991.
• Chow CK (2001). Fatty Acids in Foods and Their Health Implications. New York: Routledge Publishing. OCLC 25508943.
• Clover C (2004). The End of the Line: How overfishing is changing the world and what we eat. London: Ebury Press. ISBN 0-09-189780-7. OCLC 67383509.
• Greenberg P (2018). The Omega Principle: Seafood and the Quest for a Long Life and a Healthier Planet. New York: Penguin Press. ISBN 9781594206344. OCLC 1007552654. Archived from the original on 2023-09-18. Retrieved 2018-07-13.
• Stoll AL (2001). The Omega−3 Connection: how you can restore your body's natural balance and treat depression. Simon & Schuster. ISBN 0-684-87138-6. OCLC 670441405.

外部リンク

• Media related to Omega-3 fatty acids at Wikimedia Commons