Biochemical assessment of the nutritional status of vitamin B6 in the human

Abstract

The biochemical techniques described can furnish information as to the dietary supply of vitamin B₆ provided to the body through reflections in blood levels or in urine excretion rates of the vitamin. Such measurements would not, for the most part, distinguish between a dietary deficiency and abnormal conditions, such as poor absorption, abnormal utilization, dependency syndromes, or drug interactions. Nevertheless, such measurements can be helpful in indicating the possibility of a vitamin B₆ deficiency. More specific indications of an inadequacy of vitamin B₆ intake or reduced tissue reserves can be obtained with biochemical tests that reveal metabolic changes such as the tryptophan load test or blood transaminase activity measurements. The detection of metabolic changes indicates with a greater degree of certainty that a state of deficiency in vitamin B₆ exists more than does the mere reduction of the vitamin in biological fluids. Information obtained from performing the various biochemical tests must be interpreted and evaluated in terms of significance and compared with normal standards developed for appropriate sex and age groups. Such standards of reference are usually difficult to construct because of limited information as to normal values and ranges for various age groups, especially for children. Nevertheless, in Table 4 an attempt has been made to construct tentative guidelines for some of the biochemical measurements employed in evaluating vitamin B₆ nutritional status in the adult human. With additional controlled human studies on vitamin B₆ metabolism and with the use of the various biochemical measurements in field studies, improvements in the guidelines will be possible, particularly those applicable to children.