As of 2019, fourteen countries require food fortification of wheat flour, maize flour or rice with vitamin B 6 as pyridoxine hydrochloride. Most of these are in southeast Africa or Central America. The amounts stipulated range from 3.0 to 6.5mg/kg. An additional seven countries, including India, have a voluntary fortification program. India stipulates 2.0mg/kg. [31] Dietary supplements [ edit ] Observational studies suggested an inverse correlation between a higher intake of vitamin B 6 and all cancers, with the strongest evidence for gastrointestinal cancers. However, evidence from a review of randomized clinical trials did not support a protective effect. The authors noted that high B 6 intake may be an indicator of higher consumption of other dietary protective micronutrients. [55] A review and two observational trials reporting lung cancer risk reported that serum vitamin B 6 was lower in people with lung cancer compared to people without lung cancer, but did not incorporate any intervention or prevention trials. [56] [57] [58] Studies that highlight the use of vitamin B6 to prevent and treat health issues focus on supplements rather than food sources.

Ristilä M, Strid H, Eriksson LA, Strid A, Sävenstrand H (March 2011). "The role of the pyridoxine (vitamin B6) biosynthesis enzyme PDX1 in ultraviolet-B radiation responses in plants". Plant Physiol Biochem. 49 (3): 284–92. doi: 10.1016/j.plaphy.2011.01.003. PMID 21288732. Less severe cases present with metabolic disease associated with insufficient activity of the coenzyme pyridoxal 5’ phosphate (PLP). [1] 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 B 6 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 B 6 results in impaired glucose tolerance. [1] [15] Diagnosis [ edit ] 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. Plants synthesize pyridoxine as a means of protection from the UV-B radiation found in sunlight [5] and for the role it plays in the synthesis of chlorophyll. [6] Animals cannot synthesize any of the various forms of the vitamin, and hence must obtain it via diet, either of plants, or of other animals. There is some absorption of the vitamin produced by intestinal bacteria, but this is not sufficient to meet dietary needs. For adult humans, recommendations from various countries' food regulatory agencies are in the range of 1.0 to 2.0 milligrams (mg) per day. These same agencies also recognize ill effects from intakes that are too high, and so set safe upper limits, ranging from as low as 25mg/day to as high as 100mg/day depending on the country. Beef, pork, fowl and fish are generally good sources; dairy, eggs, mollusks and crustaceans also contain vitamin B 6, but at lower levels. There is enough in a wide variety of plant foods so that a vegetarian or vegan diet does not put consumers at risk for deficiency. [7]According to a prospective cohort study the long-term use of vitamin B 6 from individual supplement sources at greater than 20mg per day, which is more than ten times the adult male RDA of 1.7mg/day, was associated with an increased risk for lung cancer among men. Smoking further elevated this risk. [59] However, a more recent review of this study suggested that a causal relationship between supplemental vitamin B 6 and an increased lung cancer risk cannot be confirmed yet. [60] In addition, a review of 19 studies concluded that supplementing with B6, B12 and folate alone or in combination did not improve brain function or reduce the risk of Alzheimer’s ( 18).

Scientific Opinion on the substantiation of health claims related to vitamin B6". EFSA Journal. 8 (10): 1759. 2010. doi: 10.2903/j.efsa.2010.1759. a b c d e f "USDA Food Data Central. Standard Reference, Legacy Foods". USDA Food Data Central. April 2018 . Retrieved 18 August 2021.Vitamin B 6 is one of the B vitamins, and thus an essential nutrient. [1] [2] [3] [4] The term refers to a group of six chemically similar compounds, i.e., " vitamers", which can be interconverted in biological systems. Its active form, pyridoxal 5′-phosphate, serves as a coenzyme in more than 140 enzyme reactions in amino acid, glucose, and lipid metabolism. [1] [2] [3] Magnesium and vitamin B6 are said to be compatible with breastfeeding women. The recommended daily intake of vitamin B6 for lactating women is 20mg/day (equivalent to 4 tablets or 2 ampoules). The contradictory results of these studies may be due to the difference in vitamin B6 dose and study length. Mocellin S, Briarava M, Pilati P (March 2017). "Vitamin B6 and Cancer Risk: A Field Synopsis and Meta-Analysis". J Natl Cancer Inst. 109 (3): djw230. doi: 10.1093/jnci/djw230. PMID 28376200. While it appears that high doses of vitamin B6 supplements may provide anti-inflammatory benefits for people with rheumatoid arthritis over time, more research is needed.

A randomized controlled trial in 158 healthy adults who had siblings with heart disease divided participants into two groups, one that received 250 mg of vitamin B6 and 5 mg of folic acid every day for two years and another that received a placebo ( 31). Kobayashi D (2019). "[Food Poisoning by Ginkgo Seeds through Vitamin B6 Depletion]". Yakugaku Zasshi (in Japanese). 139 (1): 1–6. doi: 10.1248/yakushi.18-00136. PMID 30606915. A study in 342 women in their first 17 weeks of pregnancy found that a daily supplement of 30 mg of vitamin B6 significantly reduced feelings of nausea after five days of treatment, compared to a placebo ( 28). Research on vitamin B6 and breast cancer also shows an association between adequate blood levels of B6 and a decreased risk of the disease, especially in postmenopausal women ( 37). The classic clinical syndrome for vitamin B 6 deficiency is a seborrhoeic 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). [1]

a b c d e f g Parra M, Stahl S, Hellmann H (July 2018). "Vitamin B 6 and Its Role in Cell Metabolism and Physiology". Cells. 7 (7): 84. doi: 10.3390/cells7070084. PMC 6071262. PMID 30037155. Zhang C, Luo J, Yuan C, Ding D (2020). "Vitamin B12, B6, or Folate and Cognitive Function in Community-Dwelling Older Adults: A Systematic Review and Meta-Analysis". J Alzheimers Dis. 77 (2): 781–94. doi: 10.3233/JAD-200534. PMID 32773392. S2CID 221100310. a b c d Ghatge MS, Al Mughram M, Omar AM, Safo MK (April 2021). "Inborn errors in the vitamin B6 salvage enzymes associated with neonatal epileptic encephalopathy and other pathologies". Biochimie. 183: 18–29. doi: 10.1016/j.biochi.2020.12.025. PMID 33421502. S2CID 231437416.

A 30-day study in 36 adults with rheumatoid arthritis found that 50 mg of vitamin B6 daily corrected low blood levels of B6 but did not decrease the production of inflammatory molecules in the body ( 47). Ford AH, Almeida OP (May 2019). "Effect of Vitamin B Supplementation on Cognitive Function in the Elderly: A Systematic Review and Meta-Analysis". Drugs Aging. 36 (5): 419–34. doi: 10.1007/s40266-019-00649-w. PMID 30949983. S2CID 96435344. The assessment of vitamin B 6 status is essential, as the clinical signs and symptoms in less severe cases are not specific. [39] 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 B 6 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 10nmol/L is indicative of vitamin B 6 deficiency. [38] A PLP concentration greater than 20nmol/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 B 6 deficiency; levels of less than 3.0mmol/day is suggestive of vitamin B 6 deficiency. [38] Other methods of measurement, including UV spectrometric, spectrofluorimetric, mass spectrometric, thin-layer and high-performance liquid chromatographic, electrophoretic, electrochemical, and enzymatic, have been developed. [38] [40] Harada K (2016). "食品中の機能性成分解析"[Analysis of Functional Ingredients in Foods]. Bunseki Kagaku (in Japanese). The Japan Society for Analytical Chemistry. 65 (6): 309–319. doi: 10.2116/bunsekikagaku.65.309. ISSN 0525-1931.Mei N, Guo X, Ren Z, Kobayashi D, Wada K, Guo L (January 2017). "Review of Ginkgo biloba-induced toxicity, from experimental studies to human case reports". J Environ Sci Health C Environ Carcinog Ecotoxicol Rev. 35 (1): 1–28. doi: 10.1080/10590501.2016.1278298. PMC 6373469. PMID 28055331. Vitamin B6 may play a role in preventing eye diseases, especially a type of vision loss that affects older adults called age-related macular degeneration (AMD). A seven-year study in over 5,400 female health professionals found that taking a daily supplement of vitamin B6, B12 and folic acid (B9) significantly reduced AMD risk by 35–40%, compared to a placebo ( 43). For US food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value. For vitamin B 6 labeling purposes 100% of the Daily Value was 2.0mg, but as of May 27, 2016 it was revised to 1.7mg 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.