1. Significance and sources of pyridoxine
Domina Petric, MD

2. Significance of pyridoxine
The biological functions of the three naturally occurring forms of vitamin B6, pyridoxal, pyridoxine and pyridoxamine, depend on the metabolism of each to a common coenzyme form, pyridoxal phosphate.
That coenzyme plays critical roles in several aspects of metabolism, giving the vitamin importance in growth, cognitive development, depression, immune function, fatigue and steroid hormone activity.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

3. Significance of pyridoxine
Vitamin B6 is widespread in foods of both plant and animal origin.
Problems of primary deficiency are not prevalent.
Vitamin B6 status can be antagonized by alcohol and other factors that displace the coenzyme from its various enzymes to increase the rate of its metabolic degradation.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

4. Distribution in foods
Vitamin B6 is widely distributed in foods, occurring in greatest concentrations in meats, whole-grain products, vegetables and nuts.
In the cereal grains, vitamin B6 is concentrated primarily in the germ and aleuronic layer.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

5. Distribution in foods
Plant tissues contain mostly pyridoxine (the free alcohol form, pyridoxol).
Animal tissues contain mostly pyridoxal and pyridoxamine.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

6. Distribution in foods
A large portion of the vitamin B6 in many foods is phosphorylated or bound to proteins via the ε-amino groups of lysyl residues or the sulfhydryl groups of cysteinyl residues.
The vitamin is also found in glycosylated forms such as ′-O-(β-D-glucopyranosyl) pyridoxine.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

7. Stability
Vitamin B6 in foods is stable under acidic conditions, but unstable under neutral and alkaline conditions, particularly when exposed to heat or light.
Pyridoxine is far more stable than either pyridoxal or pyridoxamine.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

8. Stability
The cooking and thermal processing losses of vitamin B6 tend to be highly variable (0-70%):
Plant derived foods (which contain mostly pyridoxine) lose little of the vitamin.
Animal products (which contain mostly pyridoxal and pyridoxamine) lose substantial amounts.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

9. Stability
The storage losses of naturally occurring vitamin B6 from many foods can also be substantial (25-50% within a year).
Pyridoxine hydrochloride is used for food fortification and in multivitamin supplements.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

10. Bioavailability
The bioavailability of vitamin B6 in most commonly consumed foods appears to be in the range of 70-80%.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

11. Determinants of the bioavailability
Pyridoxine glycoside content
The pyridoxal-5-β-D-glycosides are poorly digested.
The presence of pyridoxine glycosides has been found to reduce the utilization of co-ingested free pyridoxine.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

12. Determinants of the bioavailability
Peptide adducts
Vitamin B6 can condense with peptide lysyl and/or cysteinyl residues during food processing, cooking or digestion.
Such products are less well utilized than the free vitamin.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

13. Determinants of the bioavailability
Peptide adducts
The reductive binding of pyridoxal and pyridoxal 5′-phosphate to ε-amino groups of lysyl residues in proteins or peptides produces adducts that not only are biologically unavailable, but that also have vitamin B6-antagonist activity.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

14. Determinants of the bioavailability
Peptide adducts
Wheat bran contains vitamin B6 in largely unavailable forms, the presence of which reduces the bioavailability of the vitamin from other foods consumed at the same time.
Plants generally contain complexed forms of pyridoxine.
Bioavailability of the vitamin of plant foods tends to be greater than that of foods derived from animals.
November 7, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

15. Literature
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc
November 7, 2018