VITAMIN B6

'Vitamin B6' is a water-soluble vitamin. Pyridoxal phosphate (PLP) is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation. PLP also is necessary for the enzymatic reaction governing the release of glucose from glycogen.

Contents

Forms

History

Sources

Deficiencies

Diagnostic Testing for B6 Deficiency

Overdose

Preventive roles and therapeutic uses

External links

References

Forms

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.

History

Vitamin B6 is a water-soluble compound that was discovered in the 1930s during nutrition studies on rats. The vitamin was named pyridoxine to indicate its structural homology to pyridine. Later it was shown that vitamin B6 could exist in two other, slightly different, chemical forms, termed pyridoxal and pyridoxamine. All three forms of vitamin B6 are precursors of an activated compound known as pyridoxal 5'-phosphate (PLP), which plays a vital role as the cofactor of a large number of essential enzymes in the human body.
Enzymes dependent on PLP focus a wide variety of chemical reactions mainly involving amino acids. The reactions carried out by the PLP-dependent enzymes that act on amino acids include transfer of the amino group, decarboxylation, racemization, and beta- or gamma-elimination or replacement. Such versatility arises from the ability of PLP to covalently bind the substrate, and then to act as an electrophilic catalyst, thereby stabilizing different types of carbanionic reaction intermediates.
Overall, the Enzyme Commission (EC; http://www.chem.qmul.ac.uk/iubmb/enzyme/) has catalogued more than 140 PLP-dependent activities, corresponding to ~4% of all classified activities.
In the early 1990s, it was suggested in megadoses as treatment for PMS and clinical depression, but this is no longer considered effective. ^[1]

Sources

The United States RDA varies between 1.3 mg and 2.0 mg, depending upon age and gender.
Vitamin B6 is prevalent in both animal and vegetable food sources. Avocados, nuts, liver, chicken, fish, green beans, field salad, wheat germ, nutritional yeast, Jolt Orange Blast, sea vegetables, and bananas are particularly good food sources.

Deficiencies

★ Supporters of a debated medical condition known as Pyroluria believe it may be one potential cause of vitamin B6 deficiency.

★ Another cause of vitamin B6 deficiency is the use of the tuberculostatic medication isoniazid, and for this reason, it is recommended to supplement with vitamin B6 when using this drug.

★ Grumpiness and irritability are also often symptomatic of a deficiency according to "Body, Mind, and the B Vitamins" by Ruth Adams and Frank Murray.

★ A meta-analysis of three databases (MEDLINE, EMBASE, and Cochrane Library), including only double-blind, randomized controlled trials, found that vitamin B6 has a significant effect compared to placebos in treating morning sickness, similar to that of ginger.^[2]
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.^[3]

Diagnostic Testing for B6 Deficiency

A positive diagnosis test for pyridoxine deficiency can be assertained by measuring erythrocyte levels of aspartate aminotransferase and transketolase in serum.

Overdose

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.^[4]
Because adverse effects have only been documented from vitamin B6 supplements and never from food sources, only the supplemental form of vitamin B6 (pyridoxine) is discussed with respect to safety. 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 (15). 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.

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.^[5] It is thought that this effect may be due to the role this vitamin plays in the conversion of tryptophan to serotonin.⁵
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.^[6]
A combination of vitamin B6 and magnesium may be an effective therapy for children with autism. While two small studies showed no effect of combined vitamin B6 and magnesium therapy,^[7][8] one larger study, alleged to be poorly-controlled showed that the B6-magnesium combination had a positive and significant behavioral effect on children with autism.^[9] In addition, two designed studies, again alleged to be poorly-designed, found that supplementation with vitamin B6 and magnesium had significant positive effects on behavior in children with autism.^[10][11]
Some studies suggest that attention deficit disorder can be helped by b6, citing improvements in hyperactivity, hyperemotivity/aggressiveness and improved school attention when combined with magnesium. ^[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 an effect of that vitamin B6 is a natural mild diuretic^[13].

External links

★ Facts about Vitamin B6 from Office of Dietary Supplements at National Institutes of Health

★ The B6 database A database of B6-dependent enzymes at University of Parma

★ Vitamin B6 Information Sheet from the Linus Pauling Institute at Oregon State University

★ Vitamin B6 (and magnesium) in the treatment of autism from the Autism Research Institute

★

References

1. http://www.webmd.com/diet/features/vitamin-pills-popping-too-many
2. Pregnancy Morning Sickness - Ginger as Effective as Vitamin B6 (open) Effectiveness and Safety of Ginger in the Treatment of Pregnancy-Induced Nausea and Vomiting (subscription), Borrelli ''et al.'', ''Obstetrics & Gynecology'', 2005;105:849-856
3. Andrews' Diseases of the Skin, 10th Edition, Elsevier.
4. Vitamin and Mineral Supplement Fact Sheets Vitamin B₆
5. Ebben, M., Lequerica, A., & Spielman A. (2002). Effects of pyridoxine on dreaming: a preliminary study. Perceptual & Motor Skills, 94(1), 135–140.
6. Increased intake of vitamin B6Sheet
7. Tolbert, L., ''et al.'' 1993. "Brief report: lack of response in an autistic population to a low dose clinical trial of pyridoxine plus magnesium." J Autism Dev Disord. 23(1):193-199.
8. Findling, R.L., ''et al.'' 1997. "High-dose pyridoxine and magnesium administration in children with autistic disorder: an absence of salutary effects in a double-blind, placebo-controlled study." J Autism Dev Disord. 27(4):467-478.
9. Martineau, J., ''et al.'' 1985. "Vitamin B6, magnesium, and combined B6-Mg: therapeutic effects in childhood autism." Biol. Psychiatry 20(5):467-478.
10. Rimland, B., ''et al.'' 1978. "The effect of high doses of vitamin B6 on autistic children: a double-blind crossover study." Am J Psychiatry 135(4):472-475.
11. Lelord, G., ''et al.'' 1981. "Effects of pyridoxine and magnesium on autistic symptoms--initial observations." J Autism Dev Disord. 11(2):219-230.
12. http://en.wikipedia.org/wiki/Attention-deficit_hyperactivity_disorder#_note-MgB6
13. THE MYSTERIOUS VITAMIN B6. By Dr. Russ Ebbets. Off The Road Column