Pyridoxic acid excretion during low vitamin B-6 intake, total fasting, and bed rest13

ing 21 d of total fasting was compared with results from 10 men consuming a diet low only in vitamin B-6 (1.76 .tmol/d) and with men consuming a normal diet during bed rest. At the end of the fast mean plasma concentrations of vitamin B-6 metabolites and un-nary excretion of 4-pyridoxic acid tended to be higher in the fasting subjects than in the low-vitamin B-6 group. The fasting subjects lost 10 / of their total vitamin B-6 pool and 13 % of their body weight. The low-vitamin B-6 group lost only 4 % of their vitamin B-6 pool. Compared with baseline, urinary excretion of pyridoxic acid was significantly increased during 17 wk of bed rest. There was no increase in pyridoxic acid excretion during a second 15-d bed rest study. These data suggest the possibility of complex interactions between diet and muscle metabolism that may influence indexes that arc frequently used to assess vitamin B-6 status. Am J C/in Nutr 1995;62:979-83. KEY WORDS Vitamin B-6, fasting, microgravity, hu