VITAMIN-B-6 REQUIREMENTS OF HUMANS

Vitamin B-6, also referred to as vitamin B-6, is the generic descripto r for all 3-hydroxy-2-methylpyridine derivatives possessing the biolog ical activity of pyridoxine. Convincing evidence of the essentiality o f the vitamin was demonstrated when hyperirritability and epileptiform -type seizures were reported in infants fed autoclaved commercial liqu id formula low in vitamin B-6; administration of the vitamin corrected these symptoms. Vitamin B-6 status and requirements have been assesse d using several methodologies. Dietary assessment usually consists of 24-h recall and/or 2-7-d intake records with nutrient composition bein g estimated using values given in the US Department of Agriculture's H andbook 8 series. Frequently used biochemical assessment methodologies include xanthurenic acid excretion after a tryptophan load, urinary 4 -pyridoxic acid level, urinary and plasma total vitamin B-6 levels, er ythrocyte alanine and aspartate aminotransferase activity coefficients , and plasma pyridoxal-5'-phosphate concentration. The most accepted v itamin B-6 status parameter is plasma pyridoxal-5'-phosphate concentra tion; however, more than one method should be utilized in evaluating s tatus. The minimum vitamin B-6 requirement of men as evaluated by diff erent researchers using various methodologies seems to be about 0.65 t o 1.25 mg/d; similar estimates have been made for women. Estimates of vitamin B-6 requirements of pregnant and lactating women range from ab out 2.1 to 7.6 mg/d; pregnancy may affect many of the parameters utili zed for assessing vitamin B-6 status. Controlled feeding studies utili zing infants, children, and adolescents are mainly lacking. Recommende d Dietary Allowances (RDAs) for vitamin B-6 have existed since 1968; t hese RDAs are based primarily on protein intake. A few other countries also have recommended intake values for the vitamin. Vitamin B-6 meta bolism and requirements may be altered in several diseases and patholo gical conditions. The symptoms for some but not all patients with thes e diseases/conditions have been reported to improve when therapeutic d oses of the vitamin are given. Vitamin B-6 has been shown to be toxic. Dosages above 200 mg pyridoxine hydrochloride/d are not recommended.