Vitamin B6

Metabolic Functions

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.

Sources

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%, 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.

Absorption

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.

Excretion

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 B6is 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. Other products of vitamin B6 metabolism that are excreted in the urine when high doses of the vitamin have been given include pyridoxal, pyridoxamine, and pyridoxine and their phosphates.

Deficiencies

The classic clinical syndrome for B6 deficiency is a seborrheic dermatitis-like eruption, atrophic glossitis with ulceration, angular cheilitis, conjunctivitis, intertrigo, and neurologic symptoms of somnolence, confusion, and neuropathy. Pyroluria is one cause of vitamin B6 deficiency.
While severe vitamin B6 deficiency results in dermatologic and neurologic changes, less severe cases present with metabolic lesions associated with insufficient acitivities of the coenzyme pyridoxal phosphate. The most prominent of the lesions is due to impaired tryptophan-niacin conversion. This can be detected based on urinary excretion of xanthurenic acid after an oral tryptophan load. Vitamin B6 deficiency can also result from impaired transsulfuration of methionine to cysteine. The pyridoxal phosphate-dependent transaminases and glycogen phosphorylase provide the vitamin with its role in gluconeogenesis, so deprivation of vitamin B6 results in impaired glucose tolerance.

A deficiency of vitamin B6 alone is relatively uncommon and often occurs in association with other vitamins of the B complex. The elderly and alcoholics have an increased risk of vitamin B6 deficiency, as well as other micronutrient deficiencies.

Toxicity

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.
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 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. of Medicine

Preventive roles and therapeutic uses

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

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 randomised 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.  Some studies suggest that the B6-magnesium combination can also help attention deficit disorder, citing improvements in hyperactivity, hyperemotivity/aggressiveness and improved school attention. 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.

Vitamin B6 is found in the following products:

ANDRO-VITO

APHRO-VITA

EREXUS

LOVE FIRE