Vitamin B6 requirements and recommendations.

The principal metabolic function of vitamin B6 is in amino acid metabolism, although the greater part of the body's vitamin B6 is in muscle, associated with glycogen phosphorylase, and the vitamin also has an important role in the actions of steroid hormones. It is usual to calculate vitamin B6 requirements relative to protein intake. An adequate intake to meet the requirements of virtually the whole population is generally considered to be 15 micrograms/g dietary protein. This is the basis of RDAs in most countries, although differences of interpretation and application of the experimental data result in widely differing recommendations from different authorities. Current RDAs range between 1.5 and 2.2 mg/d. A minimum safe intake, below which an individual would have a high probability of deficiency, is 11 micrograms/g dietary protein. Higher intakes are required in pregnancy and lactation (although there are problems in determining the requirement of the infant), and possibly also in the elderly. Average intakes of vitamin B6 in developed countries meet the target of 15 micrograms/g dietary protein, although there is biochemical evidence of inadequate vitamin B6 nutritional status in 10-25 per cent of the population. It is not know whether this has any clinical significance; it is unlikely that normal patterns of food intake would permit a significantly greater average intake of the vitamins without fortification or the use of supplements. There is little evidence that pharmacological doses of vitamin B6 have any beneficial effect. Neurological damage has been reported at extremely high intakes (in excess of 500 mg/d), and even more modest doses (50-100 mg/d) cannot be regarded as being without hazard.