Vitamin b6

Paul György, 1934

Pyridoxine, vitamin B6, which belongs to the group of B vitamins, is a water-soluble, white-crystalline substance with the molecular formula C8H11NO3 (structural formula see figure).

Pyridoxine is an alkali- and acid-resistant compound. It is sensitive to heat, oxygen and UV.

Pyridoxine occurs in 3 chemical variations with the respective 5`-phosphoric acid ester. These can easily convert into each other in vivo:

• Pyridoxol (as alcohol with CH2OH group) as provitamin
• Pyridoxal (as aldehyde with CHO group)
• Pyridoxamine (as amine with CH2NH2 group)

The active form of vitamin B6 in the organism is the phosphoric acid ester of pyridoxal, pyridoxal phosphate (PALP). PALP makes up about 60% of the vitamin B6 circulating in the body and forms the prosthetic group of numerous enzymes such as transaminases.

In amino acid metabolism, pyridoxine catalyses elimination reactions, transamination and decarboxylation in the form of pyridoxal phosphate. Furthermore, pyridoxine is involved in hematopoiesis (PALP is a cofactor in the synthesis of δ aminolevulinic acid, an intermediate product of heme synthesis), in prostaglandin synthesis and in the regulation of the water balance.

Pyridoxine is found in many animal and plant foods, including yeasts, cereal sprouts, green beans, nuts, bananas, dairy products, meat, liver, egg yolk and fish.

Pyridoxine is heat-labile and becomes ineffective by cooking and heating the food.

The requirement for pyridoxine is linked to the amount of protein turnover. It is 1.2-1.6mg/day. The requirement is increased during pregnancy. Smokers, alcoholics, women with oral contraceptives have an increased need.

For PALP the serum level can be determined. The reference range is 7.5 - 18.5 μg/l. Serum levels of PALP may be reduced by antiepileptic drugs, antidepressants and oral contraceptives.

Vitamin B6 deficiency rarely occurs in isolation but usually in combination with a Vtiamin B3 deficiency. Clinical symptoms are: loss of appetite, nausea and vomiting, diarrhoea, chronic light dermatitis, anaemia, depression, paraesthesia, sleep disorders (see alsopellagra). Vitamin B6 deficiency is mainly observed in older people (Kjeldby IK et al. 2013).

In children, a PALP deficiency can lead to hyperirritability and seizures because the synthesis of gamma-aminobutyric acid (GABA) is reduced. Pyridoxine hypovitaminosis in pregnancy increases the risk of complications during pregnancy (eclampsia, gestational diabetes).

1. Ammon H et al (2014) Hunnius Pharmaceutical Dictionary. Walter de Gruyter GmbH Berlin/Boston S 1895-1896
2. Kjeldby IK et al (2013) Vitamin B6 deficiency and diseases in elderly people--a study in nursing homes. BMC Geriatrics 13:13.