Ascorbic Acid Nutriture in the Human I. Tyrosine Metabolism and Blood Levels of Ascorbic Acid during Ascorbic Acid Depletion and Repletion

Abstract

Ten adult humans were fed a diet containing 7 mg or less of vitamin C for 78 days, and the urinary excretion of “tyrosyl” and reducing compounds, and the ascorbic acid level of serum and white cells were determined. Average serum and white cell ascorbic acid values fell to 0.3 and 13 mg %, respectively, at the end of 31 days of depletion. After 78 days they averaged 0.2 and 11.5 mg %, respectively. These levels returned to nromal when the subjects were repleted with 800 mg of ascorbic acid daily for 4 days. Of the 23 instances when serum values were less than 0.4 mg % only one white cell value was greater than 14 mg %. When serum values greater than 0.4 mg % were encountered (8 cases), no values under 14 mg % were found for white cells. On the basis of the results of this study, low blood serum ascorbic acid values (less than 0.4 mg %) would indicate a past history of poor ascorbic acid nutriture and an inadequate or deficient intake of this vitamin. There was an increase in the reducing power of the urine as the subjects became more depleted of ascorbic acid, but the urinary excretion of “tyrosyl” compounds and of reducing substances did not reach abnormal levels during the depletion period, even though 10 gm of free tyrosine were given orally to each subject during the 6 days of each metabolic period.