The three forms of vitamin B6 - pyridoxal, pyridoxine, and pyridoxamine - are widely distributed in foods like meats, grains, vegetables, and nuts. They are converted into the active coenzyme form pyridoxal phosphate, which is important for growth, cognitive function, and various metabolic processes. While deficiencies are rare, vitamin B6 status can be affected by factors like alcohol. The stability and bioavailability of the different forms vary, with pyridoxine being the most stable and plant sources generally having better bioavailability than animal sources.

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
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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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
3

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
4

5. Distribution in foods
Plant tissues contain mostly
pyridoxine (the free alcohol
form, pyridoxol).
Animal tissues contain mostly
pyridoxal and pyridoxamine.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
5

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
5′-O-(β-D-glucopyranosyl) pyridoxine.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
6

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
7

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
8

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
9

10. Bioavailability
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
10

11. Determinants of the bioavailability
Pyridoxine glycoside content
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
11

12. Determinants of the bioavailability
Peptide adducts
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
12

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
13

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.
April 17, 2018
Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
14

15. Literature
• Combs GF. The Vitamins. Fundamental Aspects in
Nutrition and Health. Elsevier Inc. 2008.
April 17, 2018 15