Vitamin B6

Overview

Pyridoxine is a water-soluble B vitamin that functions as a cofactor in more than one hundred enzyme reactions. Many of its activities are related to the metabolism of amino acids and other proteins including hemoglobin, serotonin, hormones, and prostaglandins. After entering a cell, vitamin B₆ is phosphorylated and converted into its active form, pyridoxal 5 phosphate (PLP).

Vitamin B₆ exists in three different forms. Pyridoxine occurs mainly in plants while the other two forms, pyridoxamine and pyridoxal occur mainly in animals. Since these forms have approximately the same biological activity, they are collectively referred to as vitamin B₆.

Dosage Info

Dosage Range

Not available

Most Common Dosage

20mg daily.

Dosage Forms

Tablets, capsules, liquids, liposomal sprays, and effervescent tablets.

Adult RDI

2mg

Adult ODA

10-20mg

RDA

• Infants < 6 months: 0.1mg (Adequate Intake, AI)
• Infants 7-12 months: 0.3mg (AI)
• Children 1-3 years: 0.5mg
• Children 4-8 years: 0.6mg
• Children 9-13 years: 1mg
• Males 14-50 years: 1.3mg
• Females 14-18 years: 1.2mg
• Females 19-50 years: 1.3mg
• Males >51 years: 1.7mg
• Females >51 years: 1.7mg
• Pregnancy: 1.9mg
• Lactation: 2mg

Interactions and Depletions

Interactions

• levodopa

Depletions

• Antibiotics
• Estrogen and estrogen-like medications
• hydralazine
• Loop diuretics
• isoniazid
• penicillamine
• phenelzine
• theophylline

Active Forms

Pyridoxine, pyridoxine hydrochloride, pyridoxal hydrochloride, pyridoxal-5’-phosphate.

Absorption

Each of the three forms of vitamin B₆ is readily absorbed in the intestines. The mucosal cells contain the enzyme pyridoxal kinase, which catalyzes the conversion to the active form pyridoxal phosphate.

Toxicities & Precautions

General

At appropriate doses, there are no known toxicities associated with vitamin B₆.

Side Effects

Vitamin B₆ can be neurotoxic when taken in large doses. In both case reports and clinical studies, doses of 1 to 6 grams per day have been associated with neurotoxicity. (1) , (2) Symptoms included tingling in the hands and feet, decreased muscle coordination, and a stumbling gait. All recovered without problems after discontinuing or substantially reducing their intake of the vitamin.

Functions in the Body

Regulation of Amino Acid Metabolism

Includes transamination (transfer of amino groups), deamination (removal of amino groups), desulfuration (transfer of sulfhydro groups), decarboxylation (removal of carboxyl or COOH groups)

Red Blood Cells

Necessary for the formation of hemoglobin and the growth of red blood cells.

Niacin Conversion

Essential for the conversion of tryptophan to niacin.

Neurotransmitter Production

Required for the production of neurotransmitters derived from amino acids such as serotonin, gamma amino butyric acid (GABA), norepinephrine, acetylcholine, and histamine

Energy Production

Facilitates conversion of glycogen to glucose for energy production.

Serotonin

Involved in the synthesis of serotonin

Atherosclerosis

Helps to prevent atherosclerosis by metabolizing homocysteine.

Clinical Applications

Autism

About 30 percent of autistics experience substantial improvement with high dose vitamin B₆ therapy. (3)

Carpal Tunnel Syndrome

Controversial-some studies report benefits (4) , (5) , (6) while others do not. (7)

Arthritis

Patients with rheumatoid arthritis have been found to be deficient in vitamin B6. (8)

Asthma

50mg 2 times a day dramatically decreases frequency and severity of attacks for many asthmatics. (9)

Cardiovascular Disease

Lowers elevated homocysteine. (10)

Depression

Vitamin B6 is necessary for the synthesis of serotonin. (11)

Epilepsy

Pyridoxine-dependant epilepsy. (12) , (13)

Nausea

30mg daily significantly reduced frequency and severity of vomiting episodes. (14)

PMS

50mg daily reduces symptoms for a majority of women. (15)

Kidney Stones

Prevention of calcium oxalate stones. (16)

Diabetes Mellitus

Prevention of diabetic complications. (17)

MSG Sensitivity

Chinese restaurant syndrome: vitamin B₆ is necessary to metabolize MSG. (18)

Atherosclerosis.

Homocysteine concentrations, when elevated, are a risk factor for atherosclerotic disease. Lipid lowering medications known as “fibrates” have been shown to increase homocysteine levels. A study was conducted in which fenofibrate was given either with placebo or with vitamins including vitamin B6, vitamin B12 and folic acid. The homocysteine measurements with the vitamins were significantly lower than the measurements taken without the vitamins. The investigators suggested that the “addition of these vitamins to fenofibrate may therefore be warranted for routine use.” (19) Even without the use of fenofibrate the use of vitamin B6, vitamin B12 and folic acid have lowered homocysteine. (20) Low plasma levels of vitamin B6 seemed to be an indicator for higher risk of coronary artery disease. (21) Dietary supplementation with the B-vitamins prevented hyperhomocysteinemia but did not prevent the development of vascular dysfunction or atherosclerotic lesions. (22)

In patients who have undergone angioplasty, benefit has been documented with therapy consisting of vitamin B6, vitamin B12, and folic acid. In a prospective, double-blind, randomized trial, 205 patients who had undergone a successful coronary angioplasty were given a combination of folic acid, vitamin B12, and pyridoxine or placebo for six months. Treatment significantly lowered plasma homocysteine levels and at follow-up, the minimal luminal diameter was significantly larger in the treatment group, the degree of stenosis was less severe, the rate of restenosis was significantly lower and the need for revascularization of the target lesion was less in patients assigned to folate treatment. (23)

Another randomized, double-blind placebo-controlled trial involving 553 patients was designed to evaluate the effect of homocysteine-lowering therapy on clinical outcome after percutaneous coronary intervention. After successful angioplasty of at least 1 significant coronary stenosis, patients were enrolled and randomized to either a combination of folic acid, vitamin B12, and vitamin B6 or a placebo for 6 months. After 1 year, the endpoints (death, nonfatal myocardial infarction, or revascularization) were lower in patients receiving the homocysteine lowering therapy. (24)

Cognitive Enhancement

A literature review of recent research has noted subclinical differences in nutritional status of certain B vitamins among older adults may influence certain aspects of cognitive performance. Supplementation with folate, vitamin B12 and vitamin B6 has been effective in enhancing cognitive performance in older adults. (25)

Symptoms and Causes of Deficiency

Vitamin B₆ deficiency is one of the most common nutritional deficiencies, which is partially due to large amounts being lost during cooking and food processing. A U.S. Department of Agriculture study reported that 80 percent of Americans consume less than the RDA for pyridoxine. (26)

The symptoms of vitamin B₆ deficiencies manifest primarily as dermatologic, circulatory, and neurologic problems. Because of its many metabolic roles, there are a wide variety of deficiency symptoms, which include the following: depression, sleep disturbances, nerve inflammation, PMS, lethargy, decreased alertness, anemia, altered mobility, elevated homocysteine, nausea, vomiting, and seborrheic dermatitis.

Dietary Sources

The best sources of pyridoxine are brewer’s yeast, wheat germ, organ meats (especially liver), peanuts, legumes, potatoes, and bananas. The normal flora in the human intestinal tract also synthesize vitamin B₆.

References

1. View Abstract: Berger AR, Schaumburg HH, Schroeder C, Apfel S, Reynolds R. Dose response, coasting, and differential fiber vulnerability in human toxic neuropathy: a prospective study of pyridoxine neurotoxicity. Neurology. Jul1992;42(7):1367-1370.
2. View Abstract: Wyatt KM, Dimmock PW, Jones PW, O’Brien PMS. Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review. BMJ. May1999;318:1375-1381.
3. View Abstract: Rimland B, et al. The Effect of High Doses of Vitamin B6 on Autistic Children: A Double-blind Crossover Study. Am J Psychiatry. Apr1978;135(4):472-75.
4. View Abstract: Ellis JM, et al. Response of Vitamin B-6 Deficiency and the Carpal Tunnel Syndrome to Pyridoxine. Proc Natl Acad Sci USA. Dec1982;79(23):7494-98.
5. View Abstract: Keniston RC, et al. Vitamin B6, vitamin C, and carpal tunnel syndrome. A cross-sectional study of 441 adults. J Occup Environ Med. Oct1997;39(10):949-59.
6. View Abstract: Franzblau A, et al. The relationship of vitamin B6 status to median nerve function and carpal tunnel syndrome among active industrial workers. J Occup Environ Med. May1996;38(5):485-91.
7. View Abstract: Spooner GR, et al. Using Pyridoxine to Treat Carpal Tunnel Syndrome to Pyridoxine. Can Fam Physician. Oct1993;39:2122-27.
8. View Abstract: Kremer JM, et al. Nutrient Intake of Patients with Rheumatoid Arthritis is Deficient in Pyridoxine, Zinc, Copper, and Magnesium. J Rheumatol. Jun1996;23(6):990-94.
9. View Abstract: Reynolds RD, Natta CL. Depressed Plasma Pyridoxal Phosphate Concentrations in Adult Asthmatics. Am J Clin Nut. 1985;41:684-688.
10. View Abstract: Brattstrom L, et al. Impaired Homocysteine Metabolism in Early-onset Cerebral and Peripheral Occlusive Arterial Disease. Effects of Pyridoxine and Folic Acid Treatment. Atherosclerosis. Feb1990;81(1):51-60.
11. Adams PW, et al. Effect of Pyridoxine Hydrochloride (Vitamin B6) upon Depression Associated with Oral Contraception. Lancet. Apr1973;1(7809):899-904.
12. View Abstract: Crowell GF, et al. Pyridoxine-dependent Seizures. Am Fam Physician. Mar1983;27(3):183-87.
13. View Abstract: Goto T, et al. CSF glutamate/GABA concentrations in pyridoxine-dependent seizures: etiology of pyridoxine-dependent seizures and the mechanisms of pyridoxine action in seizure control. Brain Dev. Mar2000;23(1):24-9.
14. View Abstract: Vutyavanich T, et al. Pyridoxine for Nausea and Vomiting of Pregnancy: A Randomized, Double-blind, Placebo-controlled Trial. Am J Obstet Gynecol. Sep1995;173(3 Pt 1):881-84.
15. View Abstract: Brush MG, et al. Pyridoxine in the Treatment of Premenstrual Syndrome: A Retrospective Survey in 630 Patients. Br J Clin Pract. Nov1988;42(11):448-52.
16. View Abstract: Mitwalli A, et al. Control of Hyperoxaluria with Large Doses of Pyridoxine in Patients with Kidney Stones. Int Urol Nephrol. 1988;20(4):353-59.
17. Jones CL, et al. Pyridoxine Deficiency: A New Factor in Diabetic Neuropathy. J Am Podiatry Assoc. Sep1978;68(9):646-53.
18. View Abstract: Folkers K, et al. The Biochemistry of Vitamin B6 is Basic to the Cause of the Chinese Restaurant Syndrome. Hoppe Seylers Z Physiol Chem. Mar1984;365(3):405-14.
19. View Abstract: Dierkes J, Westphal S, Kunstmann S, Banditt P, Lossner A, Luley C. Vitamin supplementation can markedly reduce the homocysteine elevation induced by fenofibrate. Atherosclerosis. Sep2001;158(1):161-4.
20. View Abstract: Woodside JV, Yarnell JW, McMaster D, Young IS, Harmon DL, McCrum EE, et al. Effect of B-group vitamins and antioxidant vitamins on hyperhomocysteinemia: a double-blind, randomized, factorial-design, controlled trial. Am J Clin Nutr. May1998;67(5):858-66.
21. View Abstract: Friso S, Girelli D, Martinelli N, et al. Low plasma vitamin B-6 concentrations and modulation of coronary artery disease risk. Am J Clin Nutr. Jun2004;79(6):992-8.
22. View Abstract: Lentz SR, Piegors DJ, Malinow MR, Heistad DD. Supplementation of atherogenic diet with B vitamins does not prevent atherosclerosis or vascular dysfunction in monkeys. Circulation. Feb2001;103(7):1006-11.
23. View Abstract: Schnyder G, Roffi M, Pin R, Flammer Y, Lange H, Eberli FR, et al. Decreased rate of coronary restenosis after lowering of plasma homocysteine levels. N Engl J Med. Nov2001:345(22):1593-600.
24. View Abstract: Schnyder G, Roffi M, Flammer Y, Pin R, Hess OM. Effect of homocysteine-lowering therapy with folic Acid, vitamin B12, and vitamin b6 on clinical outcome after percutaneous coronary intervention: the swiss heart study: a randomized controlled trial. JAMA. Aug2002;288(8):973-9.
25. View Abstract: Calvaresi E, Bryan J. B vitamins, cognition, and aging: a review. J Gerontol B Psychol Sci Soc Sci. Nov2001;56(6):P327-39.
26. Pao EM, Mickle SJ. Problem Nutrients in the United States. Food Technology. 1981;35:58-62.