Nutrition Guide

Life Stage Group RDA/AI* UL
Infants
0-6 months
7-12 months (mg/day)
0.1*
0.3* (mg/day)
ND
ND
Children
1-3 yrs
4-8 yrs
0.5
0.6
30
40
Males
9-13 yrs
14-18 yrs
19-50 yrs
50- >70 yrs
1.0
1.3
1.3
1.7
60
80
100
100
Females
9-13 yrs
13-18 yrs
19-50 yrs
50- >70 yrs
1.0
1.2
1.3
1.5
60
80
100
100
Pregnancy
<18 yrs
19-50 yrs
1.9
1.9
80
100
Lactation
<18 yrs
19-50 yrs
2.0
2.0
80
100

The Institute of Medicine notes that “No adverse effects associated with Vitamin B6 from food have been reported. This does not mean that there is no potential for adverse effects resulting from high intakes. Because data on the adverse effects of Vitamin B6 are limited, caution may be warranted. Sensory neuropathy has occurred from high intakes of supplemental forms.”[3]Click on the pdf at the end of this sentence to see the Institute of Medicine’s Dietary Reference Intake tables for vitamins.[1]

Pyridoxal phosphate has been implicated in increasing or decreasing the expression of certain genes. Increased intracellular levels of the vitamin will lead to a decrease in the transcription of glucocorticoid hormones. Also, vitamin B6 deficiency will lead to the increased expression of albumin mRNA. Also, pyridoxal phosphate will influence gene expression of glycoprotein IIb by interacting with various transcription factors. The result is inhibition of platelet aggregation.[2]

Pyridoxal phosphate aids in the synthesis of heme and can also bind to two sites on hemoglobin to enhance the oxygen binding of hemoglobin[2].

Pyridoxal phosphate is involved in the metabolism of histamine[2].

Pyridoxal phosphate is involved in almost all amino acid metabolism, from synthesis to breakdown.

1. Transamination: transaminase enzymes needed to break down amino acids are dependent on the presence of pyridoxal phosphate. The proper activity of these enzymes are crucial for the process of moving amine groups from one amino acid to another.

2. Transsulfuration: Pyridoxal phosphate is a coenzyme needed for the proper function of the enzymes cystathionine synthase and cystathionase. These enzymes work to transform methionine into cysteine.

3. Selenoamino acid metabolism: Selenomethionine is the primary dietary form of selenium. Pyridoxal phosphate is needed as a cofactor for the enzymes that allow selenium to be used from the dietary form. Pyridoxal phosphate also plays a cofactor role in releasing selenium from selenohomocysteine to produce hydrogen selenide. This hydrogen selenide can then be used to incorporate selenium into selenoproteins.[2]

4. Vitamin B6 is also required for the conversion of tryptophan to niacin and low vitamin B6 status will impair this conversion[2].

The primary role of vitamin B6 is to act as a coenzyme to many other enzymes in the body that are involved predominantly in metabolism. This role is performed by the active form, pyridoxal phosphate. This active form is converted from the two other natural forms founds in food: pyridoxal, pyridoxine and pyridoxamine.

Vitamin B6 is involved in the following metabolic processes:
Amino acid, glucose and lipid metabolism
neurotransmitter synthesis
histamine synthesis
hemoglobin synthesis and function
gene expression

Vitamin B6 is an essential component of enzymes that facilitate the biosynthesis of sphingolipids[2]. Particularly, the synthesis of ceramide requires PLP. In this reaction serine is decarboxylated and combined with palmitoyl-CoA to form sphinganine which is combined with a fatty acyl CoA to form dihydroceramide. Dihydroceramide is then further desaturated to form ceramide. In addition, the breakdown of sphingolipids is also dependent on vitamin B6 since S1P Lyase, the enzyme responsible for breaking down sphingosine-1-phosphate, is also PLP dependent.

Vitamin B6 also plays a role in gluconeogenesis. Pyridoxal phosphate can catalyze transamination reactions that are essential for the providing amino acids as a substrate for gluconeogenesis. Also, vitamin B6 is a required coenzyme of glycogen phosphorylase[2], the enzyme that is necessary for glycogenolysis to occur.

Pyridoxal phosphate, the metabolically active form of vitamin B6, is involved in many aspects of macronutrient metabolism, neurotransmitter synthesis, histamine synthesis, hemoglobin synthesis and function and gene expression. Pyridoxal phosphate generally serves as a coenzyme for many reactions and can help facilitate decarboxylation, transamination, racemization, elimination, replacement and beta-group interconversion reactions[2].

Seven forms of this vitamin are known:
pyridoxine (PN). PN is the form that is given as vitamin B6 supplement.
pyridoxine 5′-phosphate (PNP).
pyridoxal (PL).
pyridoxal 5′-phosphate (PLP). PLP is the metabolically active form.
pyridoxamine (PM).
pyridoxamine 5′-phosphate (PMP).
4-pyridoxic acid (PA). PA is the catabolite which is excreted in the urine.

All forms except PA can be interconverted.