As shown by mathematical analysis of a dependence of vitamin C excretion with urine on its content in blood as well as by plotting and mathematical interpretation of the variation curves exhibiting distribution of the ascorbic acid detected in blood plasma of persons additionally treated with vitamin C, the values 0.4-0.5 mg/dl of vitamin C (lower limit of normal values) may be recommended as a criterion of the vitamin normal consumption which corresponded to literature data. The value 0.7 mg/dl used in literature is the optimum content of vitamin C in blood. Excretion of vitamin C with urine, corresponding to lower limits of the vitamin consumption, constituted 0.4 mg/h in adults and 0.2 mg/h-in children of 5-14 years old. Metabolism of vitamin C in patients with diabetes mellitus was considerably distinct from that of healthy persons. As a criterion of normal vitamin C consumption in children of 9-13 years old impaired with diabetes mellitus, the content 1 mg/dl of vitamin C in blood plasma should be considered and its excretion with urine--more than 1.8 mg/h.