Significance and sources of pyridoxine Domina Petric, MD

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. 2008.

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. 2008.

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. 2008.

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. 2008.

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 5′-O-(β-D-glucopyranosyl) pyridoxine. November 7, 2018 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008.

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. 2008.

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. 2008.

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. 2008.

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. 2008.

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. 2008.

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. 2008.

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. 2008.

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. 2008.

Literature Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. November 7, 2018