B vitamins/ja

サプリメント > B vitamins/ja

ビタミンB群は、細胞代謝や赤血球の合成において重要な役割を果たす水溶性のビタミンの一種である。それらは化学的に多様な化合物のクラスであるが、食事では関連しており、しばしば同じ食品に一緒に含まれている。8種類すべてを含む栄養補助食品はビタミンB複合体と呼ばれる。個々のビタミンB群は、チアミンはB₁、リボフラビンはB₂、ナイアシンはB₃のように、B番号または化学名で呼ばれ、パントテン酸（B₅）、ビオチン（B₇）、葉酸（B₉）のように、番号よりも名前で認識されるものもある。

各ビタミンB群は、主要な代謝過程の補酵素（一般的には補酵素）であるか、あるいはビタミンを作るのに必要な前駆体である。

ビタミンB群のリスト

ビタミンB群のリスト

Vitamin	名称	説明
ビタミンB1	チアミン	糖やアミノ酸の異化における補酵素。
ビタミンB2	リボフラビン	FADやFMNと呼ばれる補酵素の前駆体であり、他のビタミンの活性化を含むフラボタンパク質の酵素反応に必要である。
ビタミンB3	ナイアシン (ニコチン酸)	NADとNADPと呼ばれる補酵素の前駆体であり、多くの代謝過程で必要とされる。
	Niacinamide/ja
	ニコチンアミドリボシド
ビタミンB5	パントテン酸	コエンザイムAの前駆体であるため、多くの分子の代謝に必要である。
ビタミンB6	ピリドキシン	代謝における多くの酵素反応における補酵素である。
	ピリドキサール
	ピリドキサミン
ビタミンB7	ビオチン	カルボキシラーゼ酵素の補酵素で、脂肪酸の合成や糖新生に必要である。
ビタミンB9	葉酸	DNAの生成、修復、メチル化に必要な前駆体。DNA；様々な反応の補因子；乳児期や妊娠中など、急速な細胞分裂や成長を助ける際に特に重要である。
ビタミンB12	Cobalamin/ja	ビタミンサプリメントではシアノコバラミンまたはメチルコバラミンが一般的である。すべての動物細胞の代謝に関与する補酵素で、特にDNA合成と調節に影響するが、脂肪酸代謝やアミノ酸代謝にも影響する。

注:かつてビタミンと考えられていた他の物質にもBナンバーが与えられたが、体内で製造されるか、生命維持に必須でないことが判明した時点で失格となった。4番、8、10、11番などは関連化合物を参照のこと。

摂取源

ビタミンB群は肉、卵、乳製品に豊富に含まれている。砂糖や白い小麦粉などの加工炭水化物は、加工されていないものに比べてビタミンB群が少ない傾向がある。このため、多くの国（米国を含む）では、加工後の白小麦粉にビタミンB群のチアミン、リボフラビン、ナイアシン、葉酸を戻すのが一般的である。これは、食品表示では"強化小麦粉"と呼ばれている。ビタミンB群は、七面鳥、マグロ、レバーなどの肉類に特に多く含まれている。

ビタミンB群の供給源としては、ほうれん草、豆類（豆または豆類）、全粒穀物、アスパラガス、ジャガイモ、バナナ、唐辛子、朝食用シリアルも挙げられる。 ビタミンB₁₂は植物製品からは豊富に摂取できない（ただし、発酵野菜製品、ある種の海藻、ある種のキノコには中程度の量が含まれており、これらの場合のビタミンの生物学的利用能は不明である）ため、菜食主義者にとってビタミンB₁₂欠乏は正当な懸念事項である。植物性食品の製造業者は、B₁₂の含有量を報告することがあり、どのような供給源からB₁₂が得られるかについて混乱を招いている。この混乱は、B₁₂含有量を測定するための標準的な米国薬局方（USP）法がB₁₂を直接測定しないために生じる。その代わりに、食品に対する細菌の反応を測定する。植物由来のビタミンB₁₂の化学的変異体は、細菌にとっては活性であるが、人体では利用できない。これと同じ現象が、他の種類の食品でもB₁₂含有量の著しい過大申告を引き起こすことがある。

ビタミンBの摂取量を増やす一般的な方法は、栄養補助食品を利用することである。ビタミンB群はエナジードリンクに添加されるのが一般的で、その多くは大量のビタミンB群を含んで販売されている。

ビタミンB群は水に溶けやすいため、過剰なビタミンB群は一般に容易に排泄されるが、吸収、利用、代謝には個人差がある。高齢者や運動選手は、吸収に問題があり、エネルギー産生の必要性が高まるため、ビタミンB₁₂やその他のビタミンB群の摂取量を補う必要があるかもしれない。重度の欠乏症の場合は、ビタミンB群、特にB₁₂を注射で投与して欠乏を回復させることもある。糖尿病に伴う血漿中チアミン濃度の低下とチアミンクリアランスの亢進が多いことから、1型糖尿病患者も2型糖尿病患者も、チアミンの補給を勧められることがある。また、初期胚発生における葉酸欠乏は、神経管欠損症に関連している。したがって、妊娠を計画している女性は、通常、毎日の食事からの葉酸摂取量を増やすか、サプリメントを摂取するように勧められる。

Molecular functions

Vitamin	Name	Structure	Molecular function
Vitamin B1	Thiamine		Thiamine plays a central role in the release of energy from carbohydrates. It is involved in RNA and DNA production, as well as nerve function. Its active form is a coenzyme called thiamine pyrophosphate (TPP), which takes part in the conversion of pyruvate to acetyl coenzyme A in metabolism.
Vitamin B2	Riboflavin		Riboflavin is involved in release of energy in the electron transport chain, the citric acid cycle, as well as the catabolism of fatty acids (beta oxidation).
Vitamin B3	Niacin		Niacin is composed of two structures: nicotinic acid and nicotinamide. There are two co-enzyme forms of niacin: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Both play an important role in energy transfer reactions in the metabolism of glucose, fat and alcohol. NAD carries hydrogens and their electrons during metabolic reactions, including the pathway from the citric acid cycle to the electron transport chain. NADP is a coenzyme in lipid and nucleic acid synthesis.
Vitamin B5	Pantothenic acid		Pantothenic acid is involved in the oxidation of fatty acids and carbohydrates. Coenzyme A, which can be synthesised from pantothenic acid, is involved in the synthesis of amino acids, fatty acids, ketone bodies, cholesterol, phospholipids, steroid hormones, neurotransmitters (such as acetylcholine), and antibodies.
Vitamin B6	Pyridoxine, pyridoxal, pyridoxamine		The active form pyridoxal 5'-phosphate (PLP) (depicted) serves as a cofactor in many enzyme reactions mainly in amino acid metabolism including biosynthesis of neurotransmitters.
Vitamin B7	Biotin		Biotin plays a key role in the metabolism of lipids, proteins and carbohydrates. It is a critical co-enzyme of four carboxylases: acetyl CoA carboxylase, which is involved in the synthesis of fatty acids from acetate; pyruvate CoA carboxylase, involved in gluconeogenesis; β-methylcrotonyl CoA carboxylase, involved in the metabolism of leucine; and propionyl CoA carboxylase, which is involved in the metabolism of energy, amino acids and cholesterol.
Vitamin B9	Folate		Folate acts as a co-enzyme in the form of tetrahydrofolate (THF), which is involved in the transfer of single-carbon units in the metabolism of nucleic acids and amino acids. THF is involved in purine and pyrimidine nucleotide synthesis, so is needed for normal cell division, especially during pregnancy and infancy, which are times of rapid growth. Folate also aids in erythropoiesis, the production of red blood cells.
Vitamin B12	Cobalamin		Vitamin B12 is involved in the cellular metabolism of carbohydrates, proteins and lipids. It is essential in the production of blood cells in bone marrow, and for nerve sheaths and proteins. Vitamin B12 functions as a co-enzyme in intermediary metabolism for the methionine synthase reaction with methylcobalamin, and the methylmalonyl CoA mutase reaction with adenosylcobalamin.

Deficiencies

See also: Vitamin deficiency § Water-soluble vitamins

Several named vitamin deficiency diseases may result from the lack of sufficient B vitamins. Deficiencies of other B vitamins result in symptoms that are not part of a named deficiency disease.

Vitamin	Name	Deficiency effects
Vitamin B1	Thiamine	Thiamine deficiency causes beriberi. Symptoms of this disease of the nervous system include weight loss, emotional disturbances, Wernicke encephalopathy (impaired sensory perception), weakness and pain in the limbs, periods of irregular heartbeat, and edema (swelling of bodily tissues). Heart failure and death may occur in advanced cases. Chronic thiamine deficiency can also cause alcoholic Korsakoff syndrome, an irreversible dementia characterized by amnesia and compensatory confabulation.
Vitamin B2	Riboflavin	Riboflavin deficiency can cause ariboflavinosis, which may result in cheilosis (cracks in the lips), high sensitivity to sunlight, angular cheilitis, glossitis (inflammation of the tongue), seborrheic dermatitis or pseudo-syphilis (particularly affecting the scrotum or labia majora and the mouth), pharyngitis (sore throat), hyperemia, and edema of the pharyngeal and oral mucosa.
Vitamin B3	Niacin	Niacin deficiency, along with a deficiency of tryptophan, causes pellagra. Symptoms include aggression, dermatitis, insomnia, weakness, mental confusion, and diarrhea. In advanced cases, pellagra may lead to dementia and death (the 3(+1) D's: dermatitis, diarrhea, dementia, and death).
Vitamin B5	Pantothenic acid	Pantothenic acid deficiency can result in acne and paresthesia, although it is uncommon.
Vitamin B6	Pyridoxine, pyridoxal, pyridoxamine	Vitamin B6 deficiency causes seborrhoeic dermatitis-like eruptions, pink eye and neurological symptoms (e.g. epilepsy).
Vitamin B7	Biotin	Biotin deficiency does not typically cause symptoms in adults, other than cosmetic issues such as decreased hair and nail growth, but may lead to impaired growth and neurological disorders in infants. Multiple carboxylase deficiency, an inborn error of metabolism, can lead to biotin deficiency even when dietary biotin intake is normal.
Folate	Folic acid	Folic acid deficiency results in a macrocytic anemia, and elevated levels of homocysteine. Deficiency in pregnant women can lead to birth defects, particularly neural tube defects such as spina bifida and anencephaly.
Vitamin B12	Cobalamins	Vitamin B12 deficiency results in a macrocytic anemia, elevated methylmalonic acid and homocysteine, peripheral neuropathy, sense loss, change in mobility, memory loss and other cognitive deficits. It is most likely to occur among elderly people, as absorption through the gut declines with age; the autoimmune disease pernicious anemia is another common cause. It can also cause symptoms of mania and psychosis. Untreated, it is possible to cause irreversible damage to the brain and nerve system — In rare extreme cases, paralysis can result.

Side effects

Because water-soluble B vitamins are eliminated in the urine, taking large doses of certain B vitamins usually only produces transient side effects (only exception is pyridoxine). General side effects may include restlessness, nausea and insomnia. These side effects are almost always caused by dietary supplements and not foodstuffs.

Vitamin	Tolerable Upper Intake Level (UL)	Harmful effects
Vitamin B1	None	No known toxicity from oral intake. There are some reports of anaphylaxis caused by high-dose thiamin injections into the vein or muscle. However, the doses were greater than the quantity humans can physically absorb from oral intake.
Vitamin B2	None	No evidence of toxicity based on limited human and animal studies. The only evidence of adverse effects associated with riboflavin comes from in vitro studies showing the production of reactive oxygen species (free radicals) when riboflavin was exposed to intense visible and UV light.
Vitamin B3	US UL = 35 mg as a dietary supplement	Intake of 3000 mg/day of nicotinamide and 1500 mg/day of nicotinic acid are associated with nausea, vomiting, and signs and symptoms of liver toxicity. Other effects may include glucose intolerance, and (reversible) ocular effects. Additionally, the nicotinic acid form may cause vasodilatory effects, also known as flushing, including redness of the skin, often accompanied by an itching, tingling, or mild burning sensation, which is also often accompanied by pruritus, headaches, and increased intracranial blood flow, and occasionally accompanied by pain. Medical practitioners prescribe recommended doses up to 2000 mg per day of niacin in either immediate-release or slow-release formats, to lower plasma triglycerides and low-density lipiprotein cholesterol.
Vitamin B5	None	No toxicity known.
Vitamin B6	US UL = 100 mg/day; EU UL = 25 mg/day	See Megavitamin-B6 syndrome for more information.
Vitamin B7	None	No toxicity known.
Folate	1 mg/day	Masks B12 deficiency, which can lead to permanent neurological damage.
Vitamin B12	None established	Skin and spinal lesions. Acne-like rash [causality is not conclusively established].

Discovery

Vitamin	Name	Discoverer	Date	Notes
Vitamin B1	Thiamine	Umetaro Suzuki	1910	Failed to gain publicity.
		Casimir Funk	1912
Vitamin B2	Riboflavin	D.T Smith and E.G Hendrick	1926	Max Tishler invented methods for synthesizing it.
Vitamin B3	Niacin	Conrad Elvehjem	1937
Vitamin B5	Pantothenic acid	Roger J. Williams	1933
Vitamin B6	Pyridoxine etc.	Paul Gyorgy	1934
Vitamin B7	Biotin	Research by multiple independent groups in the early 1900s; credits for discovery include Margaret Averil Boas (1927), and Dean Burk.
Vitamin B9	Folic acid	Lucy Wills	1933
Vitamin B12	Cobalamins	Five people have been awarded Nobel Prizes for direct and indirect studies of vitamin B12: George Whipple, George Minot and William Murphy (1934), Alexander R. Todd (1957), and Dorothy Hodgkin (1964).

Related compounds

Many of the following substances have been referred to as vitamins as they were once believed to be vitamins. They are no longer considered as such, and the numbers that were assigned to them now form the "gaps" in the true series of B-complex vitamins described above (for example, there is no vitamin B₄). Some of them, though not essential to humans, are essential in the diets of other organisms; others have no known nutritional value and may even be toxic under certain conditions.

• Vitamin B₄: can refer to the distinct chemicals choline, adenine, or carnitine.
  • Choline is synthesized by the human body, but not sufficiently to maintain good health, and is now considered an essential dietary nutrient.
  • Adenine is a nucleobase synthesized by the human body.
  • Carnitine is an essential dietary nutrient for certain worms, but not for humans.
• Vitamin B₈: adenosine monophosphate (AMP), also known as adenylic acid. Vitamin B₈ may also refer to inositol.
• Vitamin B₁₀: para-aminobenzoic acid (pABA or PABA), a chemical component of the folate molecule produced by plants and bacteria, and found in many foods. It is best known as a UV-blocking sunscreen applied to the skin, and is sometimes taken orally for certain medical conditions.
• Vitamin B₁₁: pteroylheptaglutamic acid (PHGA; chick growth factor). Vitamin Bc-conjugate was also found to be identical to PHGA. Derivative of folate ("pteroylmonoglutamic acid" in this nomenclature).
• Vitamin B₁₃: orotic acid.
• Vitamin B₁₄: cell proliferant, anti-anemia, rat growth factor, and antitumor pterin phosphate, named by Earl R. Norris. Isolated from human urine at 0.33ppm (later in blood), but later abandoned by him as further evidence did not confirm this. He also claimed this was not xanthopterin.
• Vitamin B₁₅: pangamic acid, also known as pangamate. Promoted in various forms as a dietary supplement and drug; considered unsafe and subject to seizure by the US Food and Drug Administration.
• Vitamin B₁₆: dimethylglycine (DMG) is synthesized by the human body from choline.
• Vitamin B₁₇: pseudoscientific name for the poisonous compound amygdalin, also known as the equally pseudoscientific name "nitrilosides" despite the fact that it is a single compound. Amygdalin can be found in various plants, but is most commonly extracted from apricot pits and other similar fruit kernels. Amygdalin is hydrolyzed by various intestinal enzymes to form, among other things, hydrogen cyanide, which is toxic to human beings when exposed to a high enough dosage. Some proponents claim that amygdalin is effective in cancer treatment and prevention, despite its toxicity and a lack of scientific evidence.
• Vitamin B₂₀: L-carnitine.
• Vitamin B_f: carnitine.
• Vitamin B_m: myo-inositol, also called "mouse antialopaecia factor".
• Vitamin B_p: "antiperosis factor", which prevents perosis, a leg disorder, in chicks; can be replaced by choline and manganese salts.
• Vitamin B_T: carnitine.
• Vitamin B_v: a type of B₆ other than pyridoxine.
• Vitamin B_W: a type of biotin other than d-biotin.
• Vitamin B_x: an alternative name for both pABA (see vitamin B₁₀) and pantothenic acid.