Vitamin B6/ja

この記事は、 ビタマーのグループについての説明である。栄養補助食品については、 ピリドキシンを参照してください。

Vitamin B6
Drug class
|ピリドキサール5'-リン酸は、ビタミンB6の代謝活性型である。
Class identifiers
Use	ビタミンB6欠乏症
ATC code	A11H
Biological target	enzyme cofactor
Clinical data
Drugs.com	International Drug Names
External links
MeSH	D025101
Legal status

ビタミンB₆はビタミンB群の一つであり、必須栄養素の一つである。この用語は、化学的に類似した6つの化合物、すなわち「ビタマー」のグループを指し、生物学的系において相互変換することができる。その活性型であるピリドキサール5′-リン酸は、アミノ酸、グルコース、脂質代謝における140以上の酵素反応において補酵素として機能する。

植物は、太陽光に含まれるUV-B放射から身を守る手段として、またクロロフィルの合成に果たす役割のために、ピリドキシンを合成する。動物は様々な形のビタミンを合成することができないため、植物や他の動物の食事から摂取しなければならない。腸内細菌]]によって産生されるビタミンの吸収も多少はあるが、食事による必要量を満たすには十分ではない。成人の場合、各国の食品規制機関が推奨する摂取量は1日あたり1.0～2.0ミリグラム（mg）である。これらの機関はまた、摂取量が多すぎることによる悪影響も認識しているため、国によって25 mg/日の低いものから100 mg/日の高いものまで、安全上限値を設定している。乳製品、卵、軟体動物、甲殻類もビタミンB₆を含むが、その量は少ない。多種多様な植物性食品には十分な量が含まれているので、ベジタリアンやビーガンの食生活を送っている消費者が欠乏症に陥る危険性はない。

食事による欠乏症はまれである。古典的な臨床症状には、口や目の周りの発疹や炎症があり、さらに眠気や手足の感覚神経や運動神経に影響を及ぼす末梢神経障害を含む神経学的影響がある。食事による不足に加えて、抗ビタミン薬物による欠乏もある。また、ビタミンB₆欠乏依存性の癲癇発作を誘発するまれな遺伝子異常が乳児に存在する。これらはピリドキサール5'-リン酸療法に反応する。

定義

ピリドキシン (PN)

ピリドキサミン (PM)

ピリドキサール (PL)

ビタミンB₆は水溶性のビタミンで、ビタミンB群の一つである。このビタミンは、実際には6つの化学的に関連した化合物、すなわちビタマーのグループから構成されており、それらはすべてそのコアとしてピリジン環を含んでいる。これらはピリドキシン、ピリドキサール、ピリドキサミン、およびそれぞれのリン酸化誘導体であるピリドキシン5'-リン酸、ピリドキサール5'-リン酸、ピリドキサミン5'-リン酸である。ピリドキサール5'-リン酸が最も高い生物学的活性を持つが、他のものはその形に変換可能である。ビタミンB₆は140以上の細胞反応において/ja|補要素として機能し、そのほとんどはアミノ酸の生合成と異化に関連するが、脂肪酸の生合成や他の生理機能にも関与する。

Forms

Because of its chemical stability, pyridoxine hydrochloride is the form most commonly given as vitamin B₆ dietary supplement. Absorbed pyridoxine (PN) is converted to pyridoxamine 5'-phosphate (PMP) by the enzyme pyridoxal kinase, with PMP further converted to pyridoxal 5'-phosphate (PLP), the metabolically active form, by the enzymes pyridoxamine-phosphate transaminase or pyridoxine 5'-phosphate oxidase, the latter of which also catalyzes the conversion of pyridoxine 5′-phosphate (PNP) to PLP. Pyridoxine 5'-phosphate oxidase is dependent on flavin mononucleotide (FMN) as a cofactor produced from riboflavin (vitamin B₂). For degradation, in a non-reversible reaction, PLP is catabolized to 4-pyridoxic acid, which is excreted in urine.

Synthesis

Biosynthesis

Main article: Pyridoxal phosphate § Biosynthesis

Two pathways for PLP are currently known: one requires deoxyxylulose 5-phosphate (DXP), while the other does not, hence they are known as DXP-dependent and DXP-independent. These pathways have been studied extensively in Escherichia coli and Bacillus subtilis, respectively. Despite the disparity in the starting compounds and the different number of steps required, the two pathways possess many commonalities. The DXP-dependent pathway:

Commercial synthesis

The starting material is either the amino acid alanine, or propionic acid converted into alanine via halogenation and amination. Then, the procedure accomplishes the conversion of the amino acid into pyridoxine through the formation of an oxazole intermediate followed by a Diels–Alder reaction, with the entire process referred to as the "oxazole method". The product used in dietary supplements and food fortification is pyridoxine hydrochloride, the chemically stable hydrochloride salt of pyridoxine. Pyridoxine is converted in the liver into the metabolically active coenzyme form pyridoxal 5'-phosphate. At present, while the industry mainly utilizes the oxazole method, there is research exploring means of using less toxic and dangerous reagents in the process. Fermentative bacterial biosynthesis methods are also being explored, but are not yet scaled up for commercial production.

Functions

PLP is involved in many aspects of macronutrient metabolism, neurotransmitter synthesis, histamine synthesis, hemoglobin synthesis and function, and gene expression. PLP generally serves as a coenzyme (cofactor) for many reactions including decarboxylation, transamination, racemization, elimination, replacement, and beta-group interconversion.

Amino acid metabolism

1. Transaminases break down amino acids with PLP as a cofactor. The proper activity of these enzymes is crucial for the process of moving amine groups from one amino acid to another. To function as a transaminase coenzyme, PLP bound to a lysine of the enzyme then binds to a free amino acid via formation of a Schiff's base. The process then dissociates the amine group from the amino acid, releasing a keto acid, then transfers the amine group to a different keto acid to create a new amino acid.
2. Serine racemase which synthesizes the neuromodulator D-serine from its enantiomer is a PLP-dependent enzyme.
3. PLP is a coenzyme needed for the proper function of the enzymes cystathionine synthase and cystathionase. These enzymes catalyze reactions in the catabolism of methionine. Part of this pathway (the reaction catalyzed by cystathionase) also produces cysteine.
4. Selenomethionine is the primary dietary form of selenium. PLP is needed as a cofactor for the enzymes that allow selenium to be used from the dietary form. PLP also plays a cofactor role in releasing selenium from selenohomocysteine to produce hydrogen selenide, which can then be used to incorporate selenium into selenoproteins.
5. PLP is required for the conversion of tryptophan to niacin, so low vitamin B₆ status impairs this conversion.

Neurotransmitters

1. PLP is a cofactor in the biosynthesis of five important neurotransmitters: serotonin, dopamine, epinephrine, norepinephrine, and gamma-aminobutyric acid.

Glucose metabolism

PLP is a required coenzyme of glycogen phosphorylase, the enzyme necessary for glycogenolysis. Glycogen serves as a carbohydrate storage molecule, primarily found in muscle, liver and brain. Its breakdown frees up glucose for energy. PLP also catalyzes transamination reactions that are essential for providing amino acids as a substrate for gluconeogenesis, the biosynthesis of glucose.

Lipid metabolism

PLP is an essential component of enzymes that facilitate the biosynthesis of sphingolipids. Particularly, the synthesis of ceramide requires PLP. In this reaction, serine is decarboxylated and combined with palmitoyl-CoA to form sphinganine, which is combined with a fatty acyl-CoA to form dihydroceramide. This compound is then further desaturated to form ceramide. In addition, the breakdown of sphingolipids is also dependent on vitamin B₆ because sphingosine-1-phosphate lyase, the enzyme responsible for breaking down sphingosine-1-phosphate, is also PLP-dependent.

Hemoglobin synthesis and function

PLP aids in the synthesis of hemoglobin, by serving as a coenzyme for the enzyme aminolevulinic acid synthase. It also binds to two sites on hemoglobin to enhance the oxygen binding of hemoglobin.

Gene expression

PLP has been implicated in increasing or decreasing the expression of certain genes. Increased intracellular levels of the vitamin lead to a decrease in the transcription of glucocorticoids. Vitamin B₆ deficiency leads to the increased gene expression of albumin mRNA. Also, PLP influences expression of glycoprotein IIb by interacting with various transcription factors; the result is inhibition of platelet aggregation.

In plants

Plant synthesis of vitamin B₆ contributes to protection from sunlight. Ultraviolet-B radiation (UV-B) from sunlight stimulates plant growth, but in high amounts can increase production of tissue-damaging reactive oxygen species (ROS), i.e., oxidants. Using Arabidopsis thaliana (common name: thale cress), researchers demonstrated that UV-B exposure increased pyridoxine biosynthesis, but in a mutant variety, pyridoxine biosynthesis capacity was not inducible, and as a consequence, ROS levels, lipid peroxidation, and cell proteins associated with tissue damage were all elevated.Biosynthesis of chlorophyll depends on aminolevulinic acid synthase, a PLP-dependent enzyme that uses succinyl-CoA and glycine to generate aminolevulinic acid, a chlorophyll precursor. In addition, plant mutants with severely limited capacity to synthesize vitamin B₆ have stunted root growth, because synthesis of plant hormones such as auxin require the vitamin as an enzyme cofactor.

Medical uses

「Pyridoxine」を参照

Isoniazid is an antibiotic used for the treatment of tuberculosis. Common side effect include numbness in the hands and feet, also known as peripheral neuropathy. Co-treatment with vitamin B₆ alleviates the numbness.

Overconsumption of seeds from Ginkgo biloba can deplete vitamin B₆, because the ginkgotoxin is an anti-vitamin (vitamin antagonist). Symptoms include vomiting and generalized convulsions. Ginkgo seed poisoning can be treated with vitamin B₆.

Dietary recommendations

The US National Academy of Medicine updated Dietary Reference Intakes for many vitamins in 1998. Recommended Dietary Allowances (RDAs), expressed as milligrams per day, increase with age from 1.2 to 1.5 mg/day for women and from 1.3 to 1.7 mg/day for men. The RDA for pregnancy is 1.9 mg/day, for lactation, 2.0 mg/day. For children ages 1–13 years the RDA increases with age from 0.5 to 1.0 mg/day. As for safety, Tolerable upper intake levels (ULs) for vitamins and minerals are identified when evidence is sufficient. In the case of vitamin B₆ the adult UL is set at 100 mg/day.

The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA. For women and men ages 15 and older the PRI is set at 1.6 and 1.7 mg/day, respectively; for pregnancy 1.8 mg/day, for lactation 1.7 mg/day. For children ages 1–14 years the PRIs increase with age from 0.6 to 1.4 mg/day. The EFSA also reviewed the safety question and set its UL at 25 mg/day.

The Japanese Ministry of Health, Labour and Welfare updated its vitamin and mineral recommendations in 2015. The adult RDAs are at 1.2 mg/day for women 1.4 mg/day for men. The RDA for pregnancy is 1.4 mg/day, for lactation is 1.5 mg/day. For children ages 1–17 years the RDA increases with age from 0.5 to 1.5 mg/day. The adult UL was set at 40–45 mg/day for women and 50–60 mg/day for men, with the lower values in those ranges for adults over 70 years of age.

Safety

Main article: Megavitamin-B6 syndrome

Adverse effects have been documented from vitamin B₆ dietary supplements, but never from food sources. Even though it is a water-soluble vitamin and is excreted in the urine, doses of pyridoxine in excess of the dietary upper limit (UL) over long periods cause painful and ultimately irreversible neurological problems. The primary symptoms are pain and numbness of the extremities. In severe cases, motor neuropathy may occur with "slowing of motor conduction velocities, prolonged F wave latencies, and prolonged sensory latencies in both lower extremities", causing difficulty in walking. Sensory neuropathy typically develops at doses of pyridoxine in excess of 1,000 mg per day, but adverse effects can occur with much less, so intakes over 200 mg/day are not considered safe. Trials with amounts equal to or less than 200 mg/day established that as a "No-observed-adverse-effect level", meaning the highest amount at which no adverse effects were observed. This was divided by two to allow for people who might be extra sensitive to the vitamin, referred to as an "uncertainty factor", resulting in the aforementioned adult UL of 100 mg/day.

Labeling

For US food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value. For vitamin B₆ labeling purposes 100% of the Daily Value was 2.0 mg, but as of May 27, 2016, it was revised to 1.7 mg to bring it into agreement with the adult RDA. A table of the old and new adult daily values is provided at Reference Daily Intake.

Sources

Bacteria residing in the large intestine are known to synthesize B-vitamins, including B₆, but the amounts are not sufficient to meet host requirements, in part because the vitamins are competitively taken up by non-synthesizing bacteria.

Vitamin B₆ is found in a wide variety of foods. In general, meat, fish and fowl are good sources, but dairy foods and eggs are not (table). Crustaceans and mollusks contain about 0.1 mg/100 grams. Fruit (apples, oranges, pears) contain less than 0.1 mg/100g.

Bioavailability from a mixed diet (containing animal- and plant-sourced foods) is estimated at being 75% – higher for PLP from meat, fish and fowl, lower from plants, as those are mostly in the form of pyridoxine glucoside, which has approximately half the bioavailability of animal-sourced B₆ because removal of the glucoside by intestinal cells is not 100% efficient. Given lower amounts and lower bioavailability of the vitamin from plants there was a concern that a vegetarian or vegan diet could cause a vitamin deficiency state. However, the results from a population-based survey conducted in the U.S. demonstrated that despite a lower vitamin intake, serum PLP was not significantly different between meat-eaters and vegetarians, suggesting that a vegetarian diet does not pose a risk for vitamin B₆ deficiency.

Cooking, storage, and processing losses vary, and in some foods may be more than 50% depending on the form of vitamin present in the food. Plant foods lose less during processing, as they contain pyridoxine, which is more stable than the pyridoxal or pyridoxamine forms found in animal-sourced foods. For example, milk can lose 30–70% of its vitamin B₆ content when dried. The vitamin is found in the germ and aleurone layer of grains, so there is more in whole wheat bread compared to white bread wheat, and more in brown rice compared to white rice.

Most values shown in the table are rounded to nearest tenth of a milligram:

Source	Amount (mg per 100 grams)
Whey protein concentrate	1.2
Beef liver, pan-fried	1.0
Tuna, skipjack, cooked	1.0
Beef steak, grilled	0.9
Salmon, Atlantic, cooked	0.9
Chicken breast, grilled	0.7
Pork chop, cooked	0.6
Turkey, ground, cooked	0.6
Banana	0.4

Source	Amount (mg per 100 grams)
Mushroom, Shiitake, raw	0.3
Potato, baked, with skin	0.3
Sweet potato baked	0.3
Bell pepper, red	0.3
Peanuts	0.3
Avocado	0.25
Spinach	0.2
Chickpeas	0.1
Tofu, firm	0.1

Source	Amount (mg per 100 grams)
Corn grits	0.1
Milk, whole	0.1 (one cup)
Yogurt	0.1 (one cup)
Almonds	0.1
Bread, whole wheat/white	0.2/0.1
Rice, cooked, brown/white	0.15/0.02
Beans, baked	0.1
Beans, green	0.1
Chicken egg	0.1

Fortification

As of 2019, fourteen countries require food fortification of wheat flour, maize flour or rice with vitamin B₆ as pyridoxine hydrochloride. Most of these are in southeast Africa or Central America. The amounts stipulated range from 3.0 to 6.5 mg/kg. An additional seven countries, including India, have a voluntary fortification program. India stipulates 2.0 mg/kg.

Dietary supplements

In the US, multi-vitamin/mineral products typically contain 2 to 4 mg of vitamin B₆ per daily serving as pyridoxine hydrochloride, but a few contain more than 25 mg. Many US dietary supplement companies also market a B₆-only dietary supplement with 100 mg per daily serving. While the US National Academy of Medicine sets an adult safety UL at 100 mg/day, the European Food Safety Authority sets its UL at 25 mg/day.

Health claims

The Japanese Ministry of Health, Labor, and Welfare (MHLW) set up the 'Foods for Specified Health Uses' (特定保健用食品; FOSHU) regulatory system in 1991 to individually approve the statements made on food labels concerning the effects of foods on the human body. The regulatory range of FOSHU was later broadened to allow for the certification of capsules and tablets. In 2001, MHLW enacted a new regulatory system, 'Foods with Health Claims' (保健機能食品; FHC), which consists of the existing FOSHU system and the newly established 'Foods with Nutrient Function Claims' (栄養機能表示食品; FNFC), under which claims were approved for any product containing a specified amount per serving of 12 vitamins, including vitamin B₆, and two minerals. To make a health claim based on a food's vitamin B₆ content, the amount per serving must be in the range of 0.3–25 mg. The allowed claim is: "Vitamin B₆ is a nutrient that helps produce energy from protein and helps maintain healthy skin and mucous membranes."

In 2010, the European Food Safety Authority (EFSA) published a review of proposed health claims for vitamin B₆, disallowing claims for bone, teeth, hair skin and nails, and allowing claims that the vitamin provided for normal homocysteine metabolism, normal energy-yielding metabolism, normal psychological function, reduced tiredness and fatigue, and provided for normal cysteine synthesis.

The US Food and Drug Administration (FDA) has several processes for permitting health claims on food and dietary supplement labels. There are no FDA-approved Health Claims or Qualified Health Claims for vitamin B₆. Structure/Function Claims can be made without FDA review or approval as long as there is some credible supporting science. Examples for this vitamin are "Helps support nervous system function" and "Supports healthy homocysteine metabolism."

Absorption, metabolism and excretion

Vitamin B₆ is absorbed in the jejunum of the small intestine by passive diffusion. Even extremely large amounts are well absorbed. Absorption of the phosphate forms involves their dephosphorylation catalyzed by the enzyme alkaline phosphatase. Most of the vitamin is taken up by the liver. There, the dephosphorylated vitamins are converted to the phosphorylated PLP, PNP and PMP, with the two latter converted to PLP. In the liver, PLP is bound to proteins, primarily albumin. The PLP-albumin complex is what is released by the liver to circulate in plasma. Protein-binding capacity is the limiting factor for vitamin storage. Total body stores, the majority in muscle, with a lesser amount in liver, have been estimated to be in the range of 61 to 167 mg.

Enzymatic processes utilize PLP as a phosphate-donating cofactor. PLP is restored via a salvage pathway that requires three key enzymes, pyridoxal kinase, pyridoxine 5'-phosphate oxidase, and phosphatases. Inborn errors in the salvage enzymes are known to cause inadequate levels of PLP in the cell, particularly in neuronal cells. The resulting PLP deficiency is known to cause or implicated in several pathologies, most notably infant epileptic seizures.

The half-life of vitamin B₆ varies according to different sources: one source suggests that the half-life of pyridoxine is up to 20 days, while another source indicates half-life of vitamin B₆ is in range of 25 to 33 days. After considering the different sources, it can be concluded that the half-life of vitamin B₆ is typically measured in several weeks.

The end-product of vitamin B₆ catabolism is 4-pyridoxic acid, which makes up about half of the B₆ compounds in urine. 4-Pyridoxic acid is formed by the action of aldehyde oxidase in the liver. Amounts excreted increase within 1–2 weeks with vitamin supplementation and decrease as rapidly after supplementation ceases. Other vitamin forms excreted in the urine include pyridoxal, pyridoxamine and pyridoxine, and their phosphates. When large doses of pyridoxine are given orally, the proportion of these other forms increases. A small amount of vitamin B₆ is also excreted in the feces. This may be a combination of unabsorbed vitamin and what was synthesized by large intestine microbiota.

Deficiency

Signs and symptoms

The classic clinical syndrome for vitamin B₆ deficiency is a seborrheic dermatitis-like eruption, atrophic glossitis with ulceration, angular cheilitis, conjunctivitis, intertrigo, abnormal electroencephalograms, microcytic anemia (due to impaired heme synthesis), and neurological symptoms of somnolence, confusion, depression, and neuropathy (due to impaired sphingosine synthesis).

In infants, a deficiency in vitamin B₆ can lead to irritability, abnormally acute hearing, and convulsive seizures.

Less severe cases present with metabolic disease associated with insufficient activity of the coenzyme pyridoxal 5' phosphate (PLP). The most prominent of the lesions is due to impaired tryptophan–niacin conversion. This can be detected based on urinary excretion of xanthurenic acid after an oral tryptophan load. Vitamin B₆ deficiency can also result in impaired transsulfuration of methionine to cysteine. The PLP-dependent transaminases and glycogen phosphorylase provide the vitamin with its role in gluconeogenesis, so deprivation of vitamin B₆ results in impaired glucose tolerance.

Diagnosis

The assessment of vitamin B₆ status is essential, as the clinical signs and symptoms in less severe cases are not specific. The three biochemical tests most widely used are plasma PLP concentrations, the activation coefficient for the erythrocyte enzyme aspartate aminotransferase, and the urinary excretion of vitamin B₆ degradation products, specifically urinary PA. Of these, plasma PLP is probably the best single measure, because it reflects tissue stores. Plasma PLP of less than 10 nmol/L is indicative of vitamin B₆ deficiency. A PLP concentration greater than 20 nmol/L has been chosen as a level of adequacy for establishing Estimated Average Requirements and Recommended Daily Allowances in the USA. Urinary PA is also an indicator of vitamin B₆ deficiency; levels of less than 3.0 mmol/day is suggestive of vitamin B₆ deficiency. Other methods of measurement, including UV spectrometric, spectrofluorimetric, mass spectrometric, thin-layer and high-performance liquid chromatographic, electrophoretic, electrochemical, and enzymatic, have been developed.

The classic clinical symptoms for vitamin B₆ deficiency are rare, even in developing countries. A handful of cases were seen between 1952 and 1953, particularly in the United States, having occurred in a small percentage of infants who were fed a formula lacking in pyridoxine.

Causes

A deficiency of vitamin B₆ alone is relatively uncommon and often occurs in association with other vitamins of the B complex. Evidence exists for decreased levels of vitamin B₆ in women with type 1 diabetes and in patients with systemic inflammation, liver disease, rheumatoid arthritis, and those infected with HIV. Use of oral contraceptives and treatment with certain anticonvulsants, isoniazid, cycloserine, penicillamine, and hydrocortisone negatively impact vitamin B₆ status. Hemodialysis reduces vitamin B₆ plasma levels.

Genetic defects

Genetically confirmed diagnoses of diseases affecting vitamin B₆ metabolism (ALDH7A1 deficiency, pyridoxine-5'-phosphate oxidase deficiency, PLP binding protein deficiency, hyperprolinaemia type II and hypophosphatasia) can trigger vitamin B₆ deficiency-dependent epileptic seizures in infants. These are responsive to pyridoxal 5'-phosphate therapy.

歴史

詳細は「ビタミン」を参照

その歴史の概要は2012年に発表されている。1934年、ハンガリーの医師パウル・ギョルギーがラットの皮膚病（肢端皮膚炎）を治す物質を発見した。彼はこの物質をビタミンB₆と命名した。ビタミンB群のナンバリングは年代順であり、パントテン酸は1931年にビタミンB₅に割り当てられていたからである。1938年、リチャード・クーンはカロテノイドとビタミン、特にビタミンB₂とビタミンB₆に関する研究でノーベル化学賞を受賞した。また1938年には、サミュエル・レプコフスキーが米ぬかからビタミンB₆を単離した。その1年後、スタントンA.ハリスとカール・アウグスト・フォルカーズはピリドキシンの構造を決定し、化学合成の成功を報告した。さらに1942年、エスモンド・エマーソン・スネルは微生物学的増殖アッセイを開発し、ピリドキシンのアミノ化産物であるピリドキサミンとピリドキシンのホルミル誘導体であるピリドキサールの特徴を明らかにした。さらなる研究により、ピリドキサール、ピリドキサミン、ピリドキシンは動物においてほぼ同等の活性を持ち、そのビタミン活性は生物がそれらを酵素的に活性な形態であるピリドキサール-5-リン酸に変換する能力に依存していることが示された。

1973年のIUPAC-IUBの勧告に従い、ビタミンB₆はピリドキシンの生物学的活性を示すすべての2-メチル,3-ヒドロキシ,5-ヒドロキシメチルピリジン誘導体の正式名称である。これらの関連化合物は同じ効果を持つため、「ピリドキシン」という言葉をビタミンB₆の同義語として使うべきではない。

研究

観察研究では、ビタミンB₆の摂取量が多いこととすべてのがんとの間に逆相関があることが示唆され、中でも消化器系のがんに対するエビデンスが最も強かった。しかしながら、ランダム化臨床試験のレビューから得られた証拠は、予防効果を支持するものではなかった。著者らは、B₆の摂取量が多いことは、他の食事性保護微量栄養素の摂取量が多いことの指標になりうると指摘している。肺がんリスクを報告したレビューおよび2件の観察試験では、血清ビタミンB₆は肺がんのない人に比べて肺がんのある人で低値であったと報告されたが、介入試験や予防試験は組み込まれていなかった。

前向きコホート研究によると、個々のサプリメントからビタミンB₆を、成人男性のRDAである1.7 mg/日の10倍以上である1日20 mg以上、長期にわたって摂取することは、男性の肺がんリスクの上昇と関連していた。喫煙はこのリスクをさらに高めた。しかし、この研究のより最近のレビューでは、ビタミンB₆のサプリメントと肺がんリスク増加との因果関係はまだ確認できないと示唆されている。

冠動脈性心疾患については、メタアナリシスにより、食事からのビタミンB₆の摂取量が0.5 mg/日増加すると相対リスクが低下することが報告されている。2021年現在、冠動脈性心疾患または心血管疾患に関するランダム化臨床試験のレビューは発表されていない。観察試験や介入試験のレビューでは、ビタミンB₆濃度が高くても治療を受けても、認知や認知症リスクに対する有意な有益性は認められなかった。食事性ビタミンB₆の低値は、女性ではうつ病のリスクの高さと相関していたが、男性では相関していなかった。治療試験をレビューしたところ、うつ病に対する意味のある治療効果は報告されなかったが、閉経前の女性を対象とした試験のサブセットでは有益性が示唆され、さらなる研究が必要であると勧告された。自閉症スペクトラム障害（ASD）と診断された小児に高用量のビタミンB₆とマグネシウムを投与したいくつかの試験の結果では、ASDの症状の重症度に対する治療効果は得られなかった。

外部リンク

• The B₆ database A database of B₆-dependent enzymes at University of Parma
• Vitamin+B6 at the U.S. National Library of Medicine Medical Subject Headings (MeSH)