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Vitamin B 6

Vitamin B 6. Grace Coughlan Dawn Dunphy Kaitlyn McDonald Carla van den Berg. Overview. Introduction to Vitamin B 6 Absorption , Transport, Metabolism, Storage, Excretion Deficiency Static and Functional Tests Gold Standard Setting the EAR Setting the UL

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Vitamin B 6

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  1. Vitamin B6 Grace Coughlan Dawn Dunphy Kaitlyn McDonald Carla van den Berg

  2. Overview Introduction to Vitamin B6 Absorption, Transport, Metabolism, Storage, Excretion Deficiency Static and Functional Tests Gold Standard Setting the EAR Setting the UL Necessary Improvements in Biochemical Assessment & Future Research Recommendations

  3. Functions of Vitamin B6 Vitamin B6 plays an important role in the metabolism of amino acids, glycogen and sphingoid bases. Serves as a coenzyme for over 100 enzymes involved in the metabolism of proteins. And because of its role in protein metabolism it plays an important role in the synthesis of heme.

  4. Functions Continued Amino acids involved in the production of the neurotransmitters serotonin, dopamine, norepinephrine, histamine, taurine and Y-aminobutyric acid are dependent on PLP. PLP is the coenzyme for the reaction that converts tryptophan to niacin. Some studies suggest that vitamin B6 may also play a role in hormonal and cell mediated immune response. (Gibson)

  5. Variations • Pyridoxine (PN) and Pyridoxine 5’-phosphate (PNP) • Pyridoxamine (PM) and Pyridoxamine 5’-phosphate (PMP) • Pyridoxal (PL) and Pyridoxal 5’-phosphate (PLP)

  6. Bioavailability B6 is about 75% bioavailable in a mixed diet. A mixed diet is typically about 15% PN.

  7. Food Sources Non-Citrus Fruits White Potatoes Fish Poultry Meat Seeds Bran Fortified Ready-To-Eat Cereals

  8. Absorption & Transportation Absorption of Vitamin B6 occurs in the gut through phosphatase-mediated hydrolysis. Here the nonphosphorylated form into the mucosal cells. The B6 is then transported through nonsaturable passive diffusion into the blood stream.

  9. Metabolism The absorbed nonphosphorylated B6 (PN, PL, PM) moves to the liver. Here the phosphate group is added back on to these compounds by reacting with PL kinase. PNP and PMP are then oxidized into PLP. A reverse reaction can occur and transform PLP into PMP.

  10. Metabolism Continued The PLP then becomes bound to proteins within tissues. The binding capacity of these proteins prevent accumulation. When the capacity is reached the liver hydrolyzes PLP and releases it into circulation as its nonphosphorylated form.

  11. Storage • The body’s vitamin B6 stores exist in a two-compartment model. • Muscle Stores and Muscle Pool

  12. Excretion • Most of the hydrolyzed vitamin B6 is released by the liver and excreted in urine. • 4-pyridoxic acid (4-PA)

  13. Plasma PLP: The Gold Standard • The major transport form of vitamin B6 in the bloodGibson • Bound to protein or freeIOM • The major form of vitamin B6 in tissuesIOM • The active coenzyme speciesIOM Pyridoxal-5’-phosphate

  14. Vitamin B6 Indicators: Direct, indirect & functional Use multiple indicators to evaluate B6 status Many tests are conducted to monitor status

  15. 1) Erythrocyte aminotransferase Two enzymes dependent on pyridoxal phosphate as coenzyme : alanine aminotransferase (A1AT) & aspartate aminotransferase (ASAT) Transfer of an amino acid to create L- glutamate In B6 deficiency, enzyme activity falls Measuring of enzyme activity in erythrocytes measures vitamin B6 status

  16. 2) Tryptophancatabolites One of the earliest markers of vitamin B6 Measuring the excretion of xanthurenic acid Catabolites follow a pathway which is PLP enzyme dependent When deficient, there is an increase in the excretion of xanthurenic acid It is not known what level of excretion represents vitamin B6 deficiency

  17. 3) Methionine Cystathinonine is dependent on B6 to break it down When vitamin B6 is inadequate, there is an increase in cystathinonine excretion because it cannot be broken down in the body The end product of cystathinonine break down is taurine, thus there will also be a decrease in taurine excretion. A level of >350 umol/day of cystathinonine means means vitamin B6 is inadequate

  18. Plasma PLP: The Gold Standard Several studies done from 1975-1986 suggested that:IOM ~ ½ of the population have plasma PLP [ ] < 30 nmol/L, but do not show vitamin B6 deficiency

  19. Plasma PLP: The Gold Standard Lui et al., 1985 proposed:IOM 20 nmol/L = Plasma PLP cutoff (No health risks)

  20. Plasma PLP: The Gold Standard > 0.05 mg Abnormal encephalogram patterns Plasma PLP [ ] = ~ 9 nmol/L Suboptimal plasma PLP [ ] = 10 nmol/L (Kretsch et al., 1991) IOM

  21. Plasma PLP: The Gold Standard Leklem, 1990:IOM Plasma PLP [ ] of 30 nmol/L = lower end of normal status

  22. Plasma PLP: The Gold Standard The Plasma PLP cutoff is therefore:IOM 20 nmol/L

  23. Setting the EAR: Men Protein interferes with vitamin B6IOM Tryptophan metabolite excretion

  24. Setting the EAR: Men Baker et al. (1964)IOM =30 g/day = 10 g challenge dose EAR < 1.25 mg PN = 1.25 mg

  25. Setting the Ear: Men Yess et al. (1964)IOM = 100 g/day EAR < 0.9 mg PN = 2 g load = 0.6 g OR =0.9 g = 0.16 mg

  26. Setting the EAR: Men Miller & Linkswiler (1967)IOM = 54 g/day OR = 150 g/day = 0.6 mg = 0.16 mg EAR < 0.76 mg PN = slow excretion over 40 days

  27. Setting the EAR: Men Linkswiler (1978) IOM = 100 g/day = 1.0-1.6 mg PN EAR < 1.0-1.5 mg PN

  28. Setting the EAR: Men Miller et al (1985) IOM = 1.6 mg > 30 nmol/L = 0.5 g/kg OR =1.0 g/kg OR =2.0 g/kg 1.5 mg > EAR

  29. Setting the EAR: Men Selhub et al. (1993) IOM = 1.3 mg Similar homocysteine [ ] EAR < 1.3 mg

  30. Setting the EAR: Men Overall Range: < 0.9 mg  < 1.9 mg EAR for Men = 1.1 mg/dayIOM

  31. Setting the EAR: Women Majority used plasma PLP [ ] as indicatorIOM

  32. Setting the EAR: Women Brown et al (1975)IOM Depletion Repletion = 78 g/day =1.0 mg OR =2.2 mg EAR just under 1.0 mg = 0.16 mg  to 24 and 60 nmol/L  5040 nmol/L

  33. Setting the EAR: Women Driskell et al (1989)IOM B6 status of 15 obese women =60 nmol/L in obese Obesity does not affect vitamin B6 status =1.18 mg =63 nmol/L in non-obese EAR < 1.2 mg

  34. Setting the EAR: Women Kretsch et al. (1995)IOM Baseline values (25 nmol/L) developed from = 1.55 g/kg = 2 mg PN Depletion Repletion EAR= 1.0 mg =0.5 mg OR =1.0 mg OR =1.5 mg OR =2.0 mg < 0.05 mg Baseline < 10 nmol/L =Restored from 1.0-1.5 mg

  35. Setting the EAR: Women Hansen et al. (1996)IOM Looked at effect of protein intake on vitamin B6 =0.5 g/kg OR =1.0 g/kg OR =2.0 g/kg > 30 nmol/L EAR considerably < 1.25 mg =20-30 nmol/L =1.25 mg PN diet Assuming PLP [ ] cutoff= 20 nmol/L…

  36. Setting the EAR: Women Hansen et al. (1996)IOM Looked at effects on status indicators from diets with low or high glucoside PN EAR < 1.5 mg • Indicators suggested lower bioavailability of glucoside = 9% B6 glucoside OR =27% B6 glucoside > 30 nmol/L

  37. Setting the EAR: Women Hansen et al. (1997)IOM = 85 g/day Baseline =1.03 mg OR =0.84 mg EAR < 0.8 mg Repletion • 3-4 different levels for 10-12 day periods

  38. Setting the EAR: Women • Huang et al. (1998)IOM = 1.55 g/kg Baseline = 1.6 mg/day Repletion EAR between 0.45-1.26 mg; most likely < 1mg =1.26 mg for 21 days =1.66 mg for 21 days =2.06 mg for 14 days Depletion = 0.45 mg/day Normalized with 1.5-2.0 mg PN

  39. Setting the EAR: Women

  40. UL & Toxicity • Vitamin B6 from food≠ toxicityIOM • Due to supplementation • UL = 100 mg • Different for children and adolescents diet.ssuppl.factsheet • High pyridoxine levelsMK

  41. UL & Toxicity M&K Akinesia Loss of balance and reflexes Altered peripheral sensation Absence of sensory nerve action potentials Convulsions

  42. UL & Toxicity Taking excess vitamin B6 during pregnancy can cause adverse effects for the infantM&K Large doses during pregnancy should be avoidedM&K

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