Vitamin B6
Vitamin B6 | |
---|---|
A11H | |
Biological target | enzyme cofactor |
Clinical data | |
Drugs.com | International Drug Names |
External links | |
MeSH | D025101 |
Legal status | |
In Wikidata |
Vitamin B6 is one of the
Plants synthesize pyridoxine as a means of protection from the
Dietary deficiency is rare. Classic clinical symptoms include rash and inflammation around the mouth and eyes, plus neurological effects that include drowsiness and peripheral neuropathy affecting sensory and motor nerves in the hands and feet. In addition to dietary shortfall, deficiency can be the result of anti-vitamin drugs. There are also rare genetic defects that can trigger vitamin B6 deficiency-dependent epileptic seizures in infants. These are responsive to pyridoxal 5'-phosphate therapy.[8]
Definition
Vitamin B6 is a water-soluble vitamin, one of the B vitamins. The vitamin actually comprises a group of six chemically related compounds, i.e., vitamers, that all contain a pyridine ring as their core. These are pyridoxine, pyridoxal, pyridoxamine, and their respective phosphorylated derivatives pyridoxine 5'-phosphate, pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. Pyridoxal 5'-phosphate has the highest biological activity, but the others are convertible to that form.[9] Vitamin B6 serves as a co-factor in more than 140 cellular reactions, mostly related to amino acid biosynthesis and catabolism, but is also involved in fatty acid biosynthesis and other physiological functions.[1][2][3]
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
Synthesis
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[10] and Bacillus subtilis, respectively. Despite the disparity in the starting compounds and the different number of steps required, the two pathways possess many commonalities.[11] The DXP-dependent pathway:
Commercial synthesis
The starting material is either the amino acid
Functions
PLP is involved in many aspects of macronutrient metabolism,
Amino acid metabolism
- D-serine from its enantiomeris a PLP-dependent enzyme.
- PLP is a coenzyme needed for the proper function of the enzymes cystathionase) also produces cysteine.
- 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.
- PLP is required for the conversion of niacin, so low vitamin B6 status impairs this conversion.[15]
Neurotransmitters
- PLP is a cofactor in the biosynthesis of five important gamma-aminobutyric acid.[6]
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.[6] PLP also catalyzes transamination reactions that are essential for providing amino acids as a substrate for gluconeogenesis, the biosynthesis of glucose.[15]
Lipid metabolism
PLP is an essential component of enzymes that facilitate the biosynthesis of
Hemoglobin synthesis and function
PLP aids in the synthesis of hemoglobin, by serving as a coenzyme for the enzyme aminolevulinic acid synthase.[6] It also binds to two sites on hemoglobin to enhance the oxygen binding of hemoglobin.[15]
Gene expression
PLP has been implicated in increasing or decreasing the expression of certain
In plants
Plant synthesis of vitamin B6 contributes to protection from sunlight.
Medical uses
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.[18] Co-treatment with vitamin B6 alleviates the numbness.[19]
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.[20][21]
Dietary recommendations
This section is missing information about definition of "milligram of B6" given the many vitamers.(September 2022) |
The US
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.[22] The EFSA also reviewed the safety question and set its UL at 25 mg/day.[23][24]
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.[25]
Safety
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.
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.[26][27] 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.[28]
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).[29][30] Crustaceans and mollusks contain about 0.1 mg/100 grams. Fruit (apples, oranges, pears) contain less than 0.1 mg/100g.[30]
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.[4] 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.[7]
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.
Most values shown in the table are rounded to nearest tenth of a milligram:
Source[29][30] | 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[29][30] | 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[30] | 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.[31]
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.
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
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.[36]
The US Food and Drug Administration (FDA) has several processes for permitting health claims on food and dietary supplement labels.[37] 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.[37] 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
Enzymatic processes utilize PLP as a phosphate-donating cofactor. PLP is restored via a
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,[38] while another source indicates half-life of vitamin B6 is in range of 25 to 33 days.[39] After considering the different sources, it can be concluded that the half-life of vitamin B6 is typically measured in several weeks.[38][39]
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.[4][40] 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.[4]
Deficiency
Signs and symptoms
The classic clinical syndrome for vitamin B6 deficiency is a
In infants, a deficiency in vitamin B6 can lead to irritability, abnormally acute hearing, and convulsive seizures.[1]
Less severe cases present with metabolic disease associated with insufficient activity of the
Diagnosis
The assessment of vitamin B6 status is essential, as the clinical signs and symptoms in less severe cases are not specific.[41] 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.[40] 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.[4] Urinary PA is also an indicator of vitamin B6 deficiency; levels of less than 3.0 mmol/day is suggestive of vitamin B6 deficiency.[40] Other methods of measurement, including UV spectrometric, spectrofluorimetric, mass spectrometric, thin-layer and high-performance liquid chromatographic, electrophoretic, electrochemical, and enzymatic, have been developed.[40][42]
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.[43]
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
Genetic defects
Genetically confirmed diagnoses of diseases affecting vitamin B6 metabolism (
History
An overview of the history was published in 2012.
Following a recommendation of IUPAC-IUB in 1973,[55] vitamin B6 is the official name for all 2-methyl,3-hydroxy,5-hydroxymethylpyridine derivatives exhibiting the biological activity of pyridoxine.[56] Because these related compounds have the same effect, the word "pyridoxine" should not be used as a synonym for vitamin B6.
Research
Observational studies suggested an
According to a prospective cohort study the long-term use of vitamin B6 from individual supplement sources at greater than 20 mg per day, which is more than ten times the adult male RDA of 1.7 mg/day, was associated with an increased risk for lung cancer among men. Smoking further elevated this risk.[61] However, a more recent review of this study suggested that a causal relationship between supplemental vitamin B6 and an increased lung cancer risk cannot be confirmed yet.[62]
For
References
- ^ a b c d e f g h i j k "Facts about Vitamin B6 Fact Sheet for Health Professionals". Office of Dietary Supplements at National Institutes of Health. February 24, 2020. Archived from the original on April 18, 2011. Retrieved February 5, 2021.
- ^ a b c d "Vitamin B6". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, OR. May 2014. Archived from the original on March 14, 2018. Retrieved March 7, 2017.
- ^ ISBN 978-0-323-66162-1.
- ^ from the original on March 6, 2022. Retrieved April 20, 2018.
- ^ PMID 19903353.
- ^ PMID 30037155.
- ^ PMID 34066199.
- ^ S2CID 231437416.
- ^ PMID 30142892.
- PMID 16157873.
- S2CID 28231094.
- PMID 23208776.
- ^ PMID 34222212.
- from the original on May 22, 2022. Retrieved August 16, 2021.
- ^ from the original on December 31, 2023. Retrieved April 20, 2018.
- from the original on January 6, 2024. Retrieved March 20, 2024.
- PMID 30718682.
- ^ "Isoniazid". The American Society of Health-System Pharmacists. Archived from the original on December 20, 2016. Retrieved August 13, 2021.
- S2CID 39197646.
- PMID 28055331.
- PMID 30606915.
- ^ "Overview on Dietary Reference Values for the EU population as derived by the EFSA Panel on Dietetic Products, Nutrition and Allergies" (PDF). 2017. Archived (PDF) from the original on August 28, 2017.
- ^ a b "Tolerable Upper Intake Levels For Vitamins And Minerals" (PDF). European Food Safety Authority. 2006. Archived (PDF) from the original on September 19, 2017.
- ^ from the original on October 24, 2020. Retrieved September 22, 2019.
- ^ "Overview of Dietary Reference Intakes for Japanese" (PDF). Ministry of Health, Labour and Welfare (Japan). 2015. Archived (PDF) from the original on October 21, 2022. Retrieved August 19, 2021.
- ^ "Federal Register May 27, 2016 Food Labeling: Revision of the Nutrition and Supplement Facts Labels" (PDF). Archived (PDF) from the original on September 22, 2017.
- ^ "Daily Value Reference of the Dietary Supplement Label Database (DSLD)". Dietary Supplement Label Database (DSLD). Archived from the original on April 7, 2020. Retrieved May 16, 2020.
- PMID 33147768.
- ^ a b c Joseph M (January 10, 2021). "30 Foods High In Vitamin B6". Nutrition Advance. Archived from the original on July 19, 2022. Retrieved August 17, 2021.
All nutritional values within this article have been sourced from the USDA's FoodData Central Database.
- ^ a b c d e f "USDA Food Data Central. Standard Reference, Legacy Foods". USDA Food Data Central. April 2018. Archived from the original on December 3, 2019. Retrieved August 18, 2021.
- ^ "Map: Count of Nutrients In Fortification Standards". Global Fortification Data Exchange. August 16, 2021. Archived from the original on April 11, 2019. Retrieved August 16, 2021.
- PMID 19087392.
- from the original on February 10, 2023. Retrieved September 23, 2021.
- ^ Shimizu T (2001). "新しい保健機能性食晶制度の概要" [Newly Established Regulation: Foods with Health Claims] (PDF). Journal of the International Life Sciences Institute of Japan (in Japanese). 66: 9–15. Archived (PDF) from the original on February 24, 2023. Retrieved September 23, 2021.
- Ministry of Health, Labor, and Welfare (in Japanese). Archived from the originalon September 23, 2021. Retrieved September 23, 2021.
ビタミンB6は、たんぱく質からのエネルギー産生と皮膚や粘膜の健康維持を助ける栄養素です.
- .
- ^ a b "Label Claims for Conventional Foods and Dietary Supplements". U.S. Food and Drug Administration. June 19, 2018. Archived from the original on August 17, 2021. Retrieved August 17, 2021.
- ^ ISBN 978-3-319-20790-2.
The half-life of pyridoxine is up to 20 days.
- ^ ISBN 978-82-8259-260-4. Archived from the original(PDF) on November 17, 2019. Retrieved December 7, 2019.
Eighty to ninety percent of vitamin B6 in the body is found in muscles and estimated body stores in adults amount to about 170 mg with a half-life of 25-33 days.
- ^ PMID 25974692.
- from the original on December 31, 2023. Retrieved April 20, 2018.
- PMID 24035968.
- from the original on December 31, 2023. Retrieved April 20, 2018.
- PMID 22288928.
- PMID 24808485.
- PMID 21967158.
- PMID 10080517.
- S2CID 22894817.
- S2CID 198496085.
- ^ S2CID 37156675.
- S2CID 4118476.
- PMID 16747297.
- ^ "The Nobel Prize in Chemistry 1938". Nobelprize.org. Archived from the original on July 8, 2018. Retrieved July 5, 2018.
- PMID 17788439.
- from the original on June 2, 2022. Retrieved August 30, 2021.
- ISSN 1831-4732.
- PMID 28376200.
- PMID 30430082.
- PMID 28922778.
- (PDF) from the original on November 21, 2023. Retrieved March 20, 2024.
- PMID 28829668.
- PMID 33376337.
- S2CID 53430399.
- S2CID 221100310.
- S2CID 96435344.
- PMID 33912967.
- PMID 15964874.
- S2CID 3999214.
External links
- 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)