[Effects of riboflavin administration on vitamin B6 metabolism].

It is shown that B2 vitamin-deficient subjects have reduced urinary excretion of 4-pyridoxic acid (4-PA) compared to normal subjects. Correlation between the total of the pyridoxal coenzymes in human plasma and 4-PA urinary excretion takes place only under adequate intake of riboflavin. The conditions under which measurements of 4-PA excretion and plasma levels of pyridoxal and pyridoxal phosphate can be used as indicators of B6-vitamin sufficiency are discussed.