Vitamin B6: Pyridoxine
Vitamin B6 is a water-soluble vitamin with functions in various body systems. The active metabolite is involved in the metabolism of several other vitamins and in the production of haemoglobin (the oxygen-carrying pigment in blood), and is also important in the synthesis of several neurotransmitters.
The requirement for vitamin B6 is related to protein intake. Frank deficiency disease is rare, but if deficiency does occur (e.g. in alcoholics or through drug-nutrient interaction) a range of symptoms such as dermatitis, sore mouth, sore tongue, and angular stomatitis (cracks at the corner of the mouth) may occur.
There are several disorders where, when low B6 status has been confirmed by blood tests, supplementation with the vitamin has been shown to be beneficial. However, in these same disorders no benefit is seen if there is no evidence of low vitamin status. Conditions where this is the case are: idiopathic carpal tunnel syndrome, where compression of the median nerve in the wrist causes pain and numbness; adult asthma (where low B6 status may be related to treatment with theophylline); and neuropathy in diabetic patients. In all of these situations the does used have been much higher than would be possible by dietary means (10-500 times the recommended nutrient intake), and it is advisable to seek medical advice before consuming such large amounts.
The potential benefits of vitamin B6 in premenstrual syndrome have been extensively studied in recent years. Large doses (500-800 mg per day) have been advocated, and have been shown to be effective in alleviating symptoms, but at these doses the potential for adverse side-effects is a cause for concern. Recent studies have shown benefit from much lower doses, i.e. about 50 mg per day.
At high doses the potential side-effects include peripheral neuropathy, numbness and tingling in the feet and hands, unsteady gait, loss of tendon reflexes, photosensitivity in sunlight, dizziness, nausea, breast tenderness, and exacerbation of acne.