Vitamin B6

It is water-soluble and thermolabile. It participates in the metabolism of many amino acids (especially tryptophan, methionine and hydroxyamino acids), the synthesis and degradation of fatty acids, sterols, thyroid hormones and porphyrins.

It catalyses, via the coenzyme pyridoxalphosphate (PLP), the activity of many aminotransferase and decarboxylase enzymes. Its consumption increases to about 5 times if the diet is very rich in fat. Vitamin B6 is used by the body for the production of lecithin, which may explain its anti-atherosclerotic action.

Its RDA ranges from 1.0 to 1.6 mg/dl in children and 2.0 to 2.2 mg/dl in adults. Its deficiency can cause asthenia, buccal irritation, glossitis, cheilosis, irritability and, in severe cases, peripheral neuropathy, anaemia and convulsions. Serum pyridoxalphosphate levels must be above 50 ng/dl. Very high dosages can cause sensory neuropathy.

Drug interactions: phenobarbital, phenytoin and primidone reduce its serum levels, chloramphenicol, isoniazid, hydralazine and oral contraceptives cause its deficiency, diuretics may increase its urinary excretion.

The most important natural sources are: wheat germ, whole grains, nuts, fish, liver, soya, meat in general.

The main plant drugs containing this vitamin are: garlic, oats, fig, ginseng, horse chestnut, raspberry, liquorice, mallow, wheat germ oil, dandelion.