Nutrition Guide

At least one preliminary study has found that this vitamin may increase dream vividness or the ability to recall dreams.[9] It is thought that this effect may be due to the role this vitamin plays in the conversion of tryptophan to serotonin.[9]

The intake of vitamin B6, from either diet or supplements, could cut the risk of Parkinson’s disease by half according to a prospective study from the Netherlands. “Stratified analyses showed that this association was restricted to smokers,” wrote the authors.[10]

Nutritional supplementation with high dose vitamin B6 and magnesium is claimed to alleviate the symptoms of autism and is one of the most popular complementary and alternative medicine choices for autism. Three small randomized controlled trials have studied this therapy; the smallest one (with 8 individuals) found improved verbal IQ in the treatment group and the other two (with 10 and 15 individuals, respectively) found no significant difference. The short-term side effects seem to be mild, but there may be significant long-term side effects of peripheral neuropathy.[11] Some studies suggest that the B6-magnesium combination can also help attention deficit disorder , citing improvements in hyperactivity, hyperemotivity/aggressiveness and improved school attention. [12]

It is also suggested that ingestion of vitamin B6 can alleviate some of the many symptoms of an alcoholic hangover and morning sickness from pregnancy. This might be due to B6’s mild diuretic effect.[13]

An overdose of pyridoxine can cause a temporary deadening of certain nerves such as the proprioceptory nerves; causing a feeling of disembodiment common with the loss of proprioception. This condition is reversible when supplementation is stopped.[7]

Because adverse effects have only been documented from vitamin B6 supplements and never from food sources, this article only discusses the safety of the supplemental form of vitamin B6 (pyridoxine). Although vitamin B6 is a water-soluble vitamin and is excreted in the urine, very high doses of pyridoxine over long periods of time may result in painful neurological symptoms known as sensory neuropathy. Symptoms include pain and numbness of the extremities, and in severe cases difficulty walking. Sensory neuropathy typically develops at doses of pyridoxine in excess of 1,000 mg per day. However, there have been a few case reports of individuals who developed sensory neuropathies at doses of less than 500 mg daily over a period of months. None of the studies, in which an objective neurological examination was performed, found evidence of sensory nerve damage at intakes of pyridoxine below 200 mg/day. In order to prevent sensory neuropathy in virtually all individuals, the Food and Nutrition Board of the Institute of Medicine set the tolerable upper intake level (UL) for pyridoxine at 100 mg/day for adults. Because placebo-controlled studies have generally failed to show therapeutic benefits of high doses of pyridoxine, there is little reason to exceed the UL of 100 mg/day. Studies have shown, however, that in the case of individuals diagnosed with autism, high doses of vitamin B6 given with magnesium may be beneficial.[8]

The products of vitamin B6 metabolism are excreted in the urine; the major product of which is 4-pyridoxic acid. It has been estimated that 40-60% of ingested vitamin B6 is oxidized to 4-pyridoxic acid. Several studies have shown that 4-pyridoxic acid is undetectable in the urine of vitamin B6 deficient subjects, making it a useful clinical marker to assess the vitamin B6 status of an individual.[2] Other products of vitamin B6metabolism that are excreted in the urine when high doses of the vitamin have been given include pyridoxal, pyridoxamine, and pyridoxine and their phosphates.

Vitamin B6 is absorbed in the jejunum and ileum via passive diffusion. With the capacity for absorption being so great, animals are able to absorb quantities much greater than what is needed for physiological demands. The absorption of pyridoxal phosphate and pyridoxamine phosphate involves their phosphorylation catalyzed by a membrane-bound alkaline phosphatase. Those products and non-phosphorylated vitamers in the digestive tract are absorbed by diffusion, which is driven by trapping of the vitamin as 5′-phosphates through the action of phosphorylation (by a pyridoxal kinase) in the jejunal mucosa. The trapped pyridoxine and pyridoxamine are oxidized to pyridoxal phosphate in the tissue.[2]

Vitamin B6 is widely distributed in foods in both its free and bound forms. Good sources include meats, whole grain products, vegetables, and nuts. Cooking, storage and processing losses of vitamin B6 vary and in some foods may be more than 50%,[4] depending on the form of vitamin present in the food. Plant foods lose the least during processing as they contain mostly pyridoxine which is far more stable than the pyridoxal or pyridoxamine found in animal foods. For example, milk can lose 30-70% of its vitamin B6 content when dried.[2]

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].