Vitamin B6 - Pyridoxine, Pyridoxal and Pyridoxamine
Introduction
Vitamin B6 is involved in the formation of body proteins, red blood cells, anti-inflamatory prostaglandins, the synthesis of brain neurotransmitters and proper function of the immune system. It is required by more than 60 different enzymes.
Absorption and Metabolism
Vitamin B6 is rapidly absorbed in the upper small intestine. After absorption, all three forms of Vitamin B6 are converted to pyridoxal phosphate, the active coenzyme form. Although pyridoxal phosphate is found in all the tissues of the body, there is no real storage. It is excreted in the urine mainly as pyridoxic acid, along with small amounts of pyridoxal and pyridoxamine.
Functions
Unlike Vitamins B1, B2, B3, biotin, and panthothenic acid, Vitamin B6 does not participate directly in energy metabolism.
Rather it is a coenzyme involved in protein metabolism, prostaglandin synthesis and immune modulation.
Protein and Amino Acid Metabolism
Transamination: e.g., conversion of alanine to pyruvate for energy production and gluconeogenesis.
Decarboxylation: in the synthesis of neurotransmitters (e.g., serotonin, norepinephrine, histamine (the vasodilator)):
histadine conversion to histamine.
Transsulfuration: transfer of a sulfur group from one amino acid to form another (i.e., serine converted to cysteine).
Side-chain transfers: conversion of methionine to cysteine.
Hemoglobin synthesis
Conversion of tryptophan to niacin.
Formation of Prostaglandins series one and three.
Myelin sheath formation around nerve cells.
Immune system support.
Recommended Daily Allowance (RDA) Vitamin B6
Classic Vitamin B6 Deficiency
Deficiency of Vitamin B6 is characterized by:
| 1. | Depression |
| 2. | Convulsions (especially in children) |
| 3. | Glucose Intolerance (B6 is needed for glucose release from liver) |
| 4. | Nausea and vomiting |
| 5. | Anemia (microcytic) |
| 6. | Impaired nerve function, peripheral neuritis, altered mobility |
| 7. | Cracking of lips and tongue |
| 8. | Seborrhea or eczema |
Vitamin B6 Supplementation
Supplementation appears to be beneficial for a number of health concerns as Vitamin B6 plays a vital role in the multiplication of all cells. It is, therefore, of critical importance to a healthy pregnancy, proper immune system function, mucous membranes, skin, and red blood cells. These tissues have a greater than average need for Vitamin B6 due to the high replication rate of these cells.1
Lowers Homocysteine (Decreasing Heart Disease Risk)
Supplementation with folic acid and Vitamin B12. Vitamin B6 also helps to lower homocysteine levels by converting homocysteine to cystathionine; as a coenzyme for cystathionine B-synthase enzyme. A recent trial included 100 mg of Vitamin B6 in patients with hyperhomocysteinemia (plus 500 mcg of folic acid) and demonstrated a successful lowering of blood homocysteine levels.2
Decreased Platelet Aggregation
Supplementation of 5 mgs per kg of body weight demonstrates a 41 percent to 48 percent reduction in platelet aggregation.3,4 However, be aware that neurotoxicity can occur at intakes above 100-150 mg per day.
Reduces Inflammatory Conditions
Vitamin B6 supplementation has been shown to be effective for carpal tunnel syndrome and premenstrual syndrome. Experimental evidence reveals that Vitamin B6 favourably affects prostaglandin synthesis increasing anti-inflammatory prostaglandin 1 and 3 (PG1 and PG3), and helping to decrease pro-inflammatory PG2.
The main biochemical interventions appear to be increasing the activity of delta-6-desaturase enzyme, which increases the conversion of alpha-linolenic acid to EPA and DHA. EPA can be converted to PG3, exerting an anti-inflammatory effect.
Typical daily dosage to control inflammatory conditions ranges from 25-100 mg.5-13 It seems plausible that Vitamin B6 supplementation can be used to help control all inflammatory conditions mediated by prostaglandin synthesis.
Autism and Attention Deficit Hyperactivity Disorder
A number of clinical trials and experimental evidence suggests that Vitamin B6 may be part of adjunctive treatment to help in these childhood conditions. Only about 20 percent of subjects may show moderate improvement and 10 percent more dramatic improvement with Vitamin B6 supplementation. Vitamin B6 is the coenzyme for brain decarboxylation enzymes, helping to synthesize dopamine, GABA, and serotonin which appear to be involved in these disorders. In this regard, Vitamin B6 appears to work best in conjunction with magnesium supplementation. The usual dosage is 25-50 mg of Vitamin B6 and 200 mg of magnesium per day.14-27
Depression (secondary to birth control pill and hormone replacement therapy)
Vitamin B6 levels are often low in females taking birth control pills or Premarin. Supplementation with 50-100 mg of Vitamin B6 per day has been shown to help reverse the depression that may result from taking these drugs.28-31
Asthma
Double-blind clinical studies show that some patients with asthma benefit from Vitamin B6 supplementation (50 mg twice daily) to correct defects in tryptophan and serotonin metabolism. Also, the asthmatic drug theophylline decreases pyridoxal-5-phosphate levels, and B6 supplementation reduces theophylline-induced side effects (headache, nausea, irritability, sleep disorders).32-35
Childhood Seizures, Tardive Dyskinesia and Epilepsy
A number of clinical trials reveal that Vitamin B6 supplementation at 50-100 mg per day may be helpful for these conditions. Be aware that doses over 80 mg may interfere with anticonvulsant therapy in epileptics.36-39
Diabetic Neuropathy
Vitamin B6 supplementation has been shown to improve diabetic neuropathy and inhibit the glycosylation of proteins, a key prognostic indicator of diabetic control and risk of complications.40,41 50-100 mg per day may be useful in this regard.
Kidney Stones
Vitamin B6 supplementation has been shown to help prevent recurrence of calcium oxalate kidney stones. This effect is best by combining B6 and magnesium supplementation. 50-100 mg of Vitamin B6 (up to 300 mg) and 200-300 mg magnesium.42,43
Vitamin B6 Toxicity
Neurotoxicity from excess Vitamin B6 intake can occur at doses as low as 100-150 mg per day, take over many months. Signs and symptoms of neurotoxicity include:
Tingling sensation in feet
Loss of muscle coordination
Degeneration of nerve tissue
Therefore, it is best to limit Vitamin B6 supplementation to 50 mg. In some instances it can be taken up to 100 mg per day in divided doses.44-47
Drug-Nutrient Interactions
Pregnancy and Lactation
1. During pregnancy and lactation, the only supplements that are considered safe include standard prenatal vitamin and mineral supplements. All other supplements or dose alterations may pose a threat to the developing fetus and there is generally insufficient evidence at this time to determine an absolute level of safety for most dietary supplements other than a prenatal supplement. Any supplementation practices beyond a prenatal supplement should involve the cooperation of the attending physician (i.e., magnesium and the treatment of preeclampsia.)
References: Pregnancy and Lactation
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