General Description
Vitamin B-6 is a water-soluble vitamin in the B-complex vitamin
group. The B vitamins are used by the body as coenzymes, which make
biochemical reactions possible. B-6 consists of three substances,
pyridoxine, pyridoxal phosphate, and pyridoxamine. All three forms
can be utilized by the human body, but only pyridoxine is officially
designated as B-6. Pyridoxine deficiency can result in skin and
nervous system disorders, dizziness, convulsions, kidney stones,
and anemia.
Food sources
Vitamin B-6 is found in foods such as meats and organ meats, poultry,
whole-grain cereals and bread, avocadoes, spinach, green beans,
sunflower seeds, and bananas.
Health applications
Functions and uses
Vitamin B-6 enables many enzymatic reactions in the body. The brain
and central nervous system require B-6 as a catalyst for the formation
of their chemical transmitters. B-6 is needed for the conversion
of carbohydrates into energy, and of tryptophane into nicotinic
acid (vitamin B-3). It also plays a role in the formation of red
blood cells and the metabolism of amino acids.
Homocysteine
Many of the health benefits provided by pyridoxine relate to its
role in controlling plasma homocysteine levels. High blood homocysteine
levels may contribute to thrombosis,1 atherosclerosis,1,2,3
coronary artery disease,3,4 and cardiovascular
disease.5 Studies indicate that pyridoxine
can reduce plasma homocysteine levels and that this action is
enhanced by the inclusion of folic acid.3
Tardive dyskinesia
There is conflicting evidence regarding the efficacy of pyridoxine
in treating tardive dyskinesia. Early studies were not encouraging,
however there is case study evidence which suggests that pyridoxine
may reduce the frequency and intensity of the involuntary movements
associated with the disorder.6,7
Asthma
In one case study, 76 children with severe bronchial asthma were
treated daily with 200 mg of pyridoxine, while their dosage of
bronchodilators and cortisone was reduced. The study indicates
that each showed improvement in their symptoms from this 5 month
treatment.8 However, other studies indicate
that pyridoxine does not improve the symptoms of severe asthma
and that such treatment is unjustified.9
Kidney Stones
Studies suggest that large treatments of pyridoxine may decrease
oxalate production, and that this may help prevent calcium oxalate
kidney stone formation.10,11 However, more
long-term studies are needed to further elucidate its effectiveness
as a viable and consistent treatment for those at risk of kidney
stones.
Autism
Linus Pauling's orthomolecular hypothesis states that some forms
of disease and mental illness are related to biochemical errors
in the body. There is evidence that vitamin therapy can counteract
some of these errors. For example, studies demonstrate that pyridoxine
and magnesium supplementation may improve many symptoms of autism.13-17
Researchers cite clinical as well as empirical evidence in support
of this therapy, but additional long-term studies are needed before
definitive conclusions can be drawn.12
Premenstrual syndrome
There is conflicting evidence as to the efficacy of pyridoxine
in the treatment of depression related to premenstrual syndrome.18
Some trials demonstrate that pyridoxine can improve PMS-induced
depression,19 however there are no significant
conclusions on the subject. Long term intake of B-6 at high doses
can be toxic. Therefore, regarding pyridoxine and PMS-induced
depression, it is generally recommended that a normal dietary
intake of pyridoxine may provide the most benefits with the least
risk.
Dosage and Toxicity
If taken in large doses, B-6 can cause varied neurological symptoms
such as numbness in the hands and feet, and a general loss in
sensory perception. It is generally considered nontoxic when taken
in doses up to 100 mg daily. Because B-6 is needed to process
protein, an increased dietary intake of protein necessitates increased
consumption of B-6. The RDI recommendation is 2 mg of vitamin
B-6 for every 100 grams of dietary protein.
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