Vitamin B6 (pyridoxine) is a very important B vitamin, which participates in the synthesis of proteins and structural compounds of the organism, neurotransmitters in the nervous system and prostaglandins and in the maturation of red blood cells.
Vitamin B6 is also essential for maintaining hormonal balance and good immune function.
Food sources
Good sources of vitamin B6 are whole grains, legumes, bananas, seeds and nuts, potatoes, Brussels sprouts and cauliflowers (see table 11.1). Vitamin B6 levels within cells show a complex correlation with dietary magnesium content.
Signs and symptoms of deficiency
Vitamin 96 deficiency is characterized by depression, seizures (especially in children), glucose intolerance, anemia, impaired nerve function, chapped lips and tongue, and seborrhea or eczema (1). Although absolute vitamin B6 deficiency is quite rare, numerous clinical studies demonstrate the importance of the vitamin in several conditions that typically react to vitamin B6 supplements, such as asthma, PMS, carpal tunnel syndrome, depression, morning sickness and kidney stones.
The increase in the incidence of these disorders from the 1950s onwards paralleled that of the level of vitamin B6 antagonists present in foods or used as drugs during that same period. Vitamin B6 antagonists are hydrazine dyes (especially FD&C yellow # 5), some drugs (isoniazid, hydralazine, dopamine and penicillamine), oral contraceptives, alcohol and excessive protein consumption.
Intake of yellow dye # 5 (tartrazine) is often higher (per capita intake of 15 milligrams per day) than the recommended daily allowance for vitamin B6, which is 2.0 milligrams for males and 1.6 milligrams for the females.
Beneficial effects
The human body needs vitamin B6 for the proper functioning of over 60 different enzymes. Pyridoxine plays a vital role in the multiplication of each cell and is therefore of critical importance for a regular pregnancy and for the proper functioning of the immune system, mucous membranes, skin and red blood cells.
These tissues have an above-average need for vitamin B6 since they are formed by cells in active replication and a deficiency of this vitamin seriously compromises their function. Pyridoxine, participating in the synthesis of all amino acid neurotransmitters (such as serotonin, dopamine, melatonin, adrenaline, noradrenaline, etc.), also plays a fundamental role in the biochemical metabolism of the brain.
Forms available
Vitamin B6 is available in the form of pyridoxine hydrochloride and pyridoxal-5-phosphate, which is the most active form.
However, it must be remembered that intestinal cells remove the phosphate molecule from most of the ingested pyridoxal-5-phosphate, before its absorption (2).
If the cofactors necessary for the conversion (riboflavin and magnesium) are available, the pyridoxine form satisfies the needs sufficiently in most individuals with the exception of subjects suffering from liver disease (especially liver cirrhosis), in which, since the activation of pyridoxine in pyridoxal-5-phosphate occurs in the liver, the conversion of pyridoxine to pyridoxal-5-phosphate may not be adequate. In liver cirrhosis, and possibly other liver diseases as well, supplements in the form of pyridoxal-5-phosphate injections may be more beneficial than pyridoxine
Warnings and Precautions
Vitamin B6 is one of the few water-soluble vitamins that exhibit some toxicity when taken in high or moderate doses for long periods of time.
Doses greater than 2000 mg per day can cause symptoms of neurotoxicity in some individuals (sensation of form and oil in the feet, loss of muscle coordination and degeneration of nerve tissue). Chronic intakes of dosages greater than 500 milligrams per day can be toxic if prolonged for many months or years (4).
There are also some rare reports of toxicity manifested in the case of chronic long-term intake of doses of 150 mg per day (5-7).
Researchers believe that the toxicity is due to the fact that, as the liver's ability to add a phosphate group to form the active form of vitamin B6 (pyridoxal-5-phosphate) is limited, the excess pyridoxine is toxic to nerve cells. or that it actually acts as an antimetabolite by binding to pyridoxal-5-phosphate receptors and causing a relative deficiency of vitamin B6 · Once again it seems reasonable to limit the dose to 50 mg.
If you want a higher dose, split the dosage over the day.
Interaction
Riboflavin and magnesium are needed to convert pyridoxine to pyridoxal-5-phosphate. Vitamin B6 significantly interacts with magnesium and zinc; pyridoxine supplements can increase the intracellular concentrations of these essential minerals. There are many B6 antagonists, including food coloring (especially FD&C yellow # 5). some drugs (isoniazid, hydralazine, dopamine and penicillamine), oral contraceptives, alcohol, and excessive protein intake.
1. Driskell JA, Vitamin B6 requirements of humans. Nutr Res 14, 293-324, 1994.
2. Middleton HM. Intestinal absorption of pyridoxal-Sphosphate, Disappearance from perfused segments of rat jejunum in vivo. J Nutr 109, 975-981, 1979.
3. Labadarios D, et al., Vitamin B6 deficiency in chronic liver disease-evidence for increased degradation of pyridoxal-5-phosphate. Gut 18, 23-27, 1977.
4. Cohen M and Bendich A. Safety of pyridoxine-A review of human and animal studies. Toxicol Letters 34, 129-139, 1986.
5. Parry GJ and Bredesen DE, Sensory neuropathy with low-dose pyridoxine. Neurology 35, 1466-1468, 1985.
6. Waterston JA and Gilligan BS, Pyridoxine neuropathy. Med J Aust 146, 640-642, 1987.
7. Dalton K and Dalton MJT, Characteristics of pyridoxine overdose neuropathy syndrome. Acta Neurol Scand 76, 8, 1987.
