Vitamin B6
Vitamin B6 is the general term for 6 water-soluble vitamins with vitamin B6 activity.
Some of the B6 group are essential cofactors for enzymes involved in numerous metabolic processes. They function in the nervous system, for haemoglobin synthesis and function, for tryptophan metabolism, hormone function and nucleic acid synthesis. Date of preparation: December 2018
Contribution:
Importance of vitamin B6 for health
Vitamin B6 is the general term for 6 water-soluble vitamins with vitamin B6 activity: pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM), and their respective 5’-phosphate esters (PLP, PNP, PMP) (1-3). PLP is an essential cofactor for enzymes involved in numerous metabolic processes, which are categorized in 5 Fold Types (2):
I: aspartate aminotransferase family
II: tryptophan synthase family
III: alanine racemase family
IV: D-amino acid aminotransferase family
V: glycogen phosphorylase family
Metabolic functions of PLP include (2, 4):
- Nervous system function
- Haemoglobin synthesis and function
- Tryptophan metabolism
- Hormone function
- Nucleic acid synthesis
Human are incapable of de novo vitamin B6 synthesis, thus this vitamin needs to be provided through diet. Absorption is occurring in the jejunum by non-saturable, passive diffusion of the non-phosphorylated forms. PL is the main form that enters the portal circulation and binds to albumin for transport in the plasma. 75-80% of the circulating vitamin B6 is present as PL and PLP, with 60% of PLP located in the erythrocytes. Phosphorylation of the free forms is mainly located in the liver; a FMN-dependent oxidase coverts PNP and PMP to PLP (4, 5).
Various foods contain good amounts of vitamin B6. Fish, beef liver and organ meats, potatoes and other starchy vegetables, and non-citrus fruit are good sources. A diverse dietary intake is estimated to result in a 75% bioavailability of this vitamin (2, 3).
Risks
Severe vitamin B6 deficiency is rare. Low vitamin B6 status is commonly associated with inadequate vitamin B12 and folate status. Reported deficiency symptoms include abnormal electroencephalogram patterns, seizures, neurologic disorders such as depression and confusion, inflammation on the tongue, sores and ulcers of the mouth and skin. Individuals with impaired renal function, autoimmune disorders, and alcoholics are at risk for vitamin B6 inadequacy (2, 3).
Symptoms of high vitamin B6 intake include sensory neuropathy, dermatological lesions, photosensitivity, and gastrointestinal symptoms, nausea, or heartburn. Tolerable Upper Limits (UL) have been established by the Food and Nutrition Board (3).
Vitamin B6 metabolism is affected by certain medications (2): Oral contraceptives, Anti-tuberculosis medications, Penicillamine, Anti-parkinsonian drugs, Methylxanthines for respiratory conditions.