THE EXCRETION RATES OF VITAMINS AND THEIR METABOLITES AS CRITERIA OF VITAMIN-B2, VITAMIN-B6 AND NIACIN AVAILABILITY

Alimentary deficiency of riboflavin in rats caused a decrease in excretion of vitamin B2 with urine simultaneously with lowering in daily excretion of 4-pyridoxylic acid (4-PA) and N1-methyl nicotinamide (N1-MNA); these patterns are usually used as indicators of pyridoxine and niacin availability. The similar decrease in excretion of 4-PA and N1-MNA with urine but without alterations in NAD+NADP concentrations in erythrocytes was detected in women deficient in vitamin B2. Content of nicotinamide coenzymes in erythrocytes correlated with excretion of N1-MNA with urine only under normal conditions of riboflavin availability. Use of the criteria involving rates of 4-PA and N1-MNA excretion for evaluation of pyridoxine and niacin deficiency is discussed.