We have reported previously that the urinary excretion of B-group vitamins reflects
recent dietary intakes of these vitamins. We also proposed reference values for the
urinary levels of B-group vitamins for human subjects, and used these for evaluating human
nutritional status. However, the question arises as to whether the urinary excretion of
B-group vitamins in animals or human subjects decreases immediately before they become
B-group vitamin insufficient or when fed a diet low in vitamins. In the present study,
rats were fed a vitamin-free diet for 5 d, and changes in the levels of B-group vitamins
in urine and blood were monitored. Urinary excretion of vitamin B1, vitamin
B2, 4-pyridoxic acid (a catabolite of vitamin B6), pantothenic
acid, folate and biotin steeply decreased, and all of the values reached zero within
1–2 d. With respect to blood, the concentrations of only three of the eight B-group
vitamins (vitamin B1, pyridoxal phosphate and biotin) decreased to 15 %
(P < 0·0001), 7 % (P < 0·0001) and 2 %
(P < 0·0001) on day 5, respectively, compared with the values at
the beginning of the experiment. The decrease was more rapid and the changes were greater
in the urine samples than in the blood samples. The present data complement our previous
proposal that the urinary excretion of B-group vitamins reflects the nutritional status of
these vitamins.