Ascorbic acid vitamin body pool

Mobilization and Metabolism. The total ascorbic acid body pool in healthy adults has been estimated to be approximately 1.5 g, which increases to 2.3—2.8 g with intakes of 200 mg/d (151—158). Depletion of the body pool to 600 mg initiates physiological changes, and signs of clinical scurvy are reported when the body pool falls below 300 mg (149). Approximately 3—4% of the body pool turns over daily, representing 40—60 mg/d of metabolized, or consumed, vitamin C. Smokers have a higher metaboHc turnover rate of vitamin C (approximately 100 mg/d) and a lower body pool than nonsmokers, unless compensated through increased daily intakes of vitamin C (159). The metaboHsm of ascorbic acid varies among different species. 

C is rapidly excreted. About 4% of this pool is lost daily (fractional catabolic rate) after intermission of vitamin C supply. The biological half-time of the pool is therefore approximately 8-40 days (Homig, 1981). The first symptoms of scurvy occur upon reaching a total body pool of 300-400 mg. Table II shows data on the turnover rate of ascorbic acid for man and different species. Table III shows the ascorbic acid concentrations in organs and body fluids of the adult man. 

The minimum vitamin C requirement to prevent the development of scurvy has been found to be 10 mg/day (Hodges et al., 1971). This supply is not sufficient for the provision of acceptable reserves of the vitamin. The intake of 10 mg ascorbic acid per day reflects a plasma concentration of 7.6-14.1 p,mol/liter (0.13-0.24 mg/100 ml), a concentration that is far from tissue saturation. The renal clearance of ascorbic acid rises sharply at a point of 82 xmol/liter (1.4 mg/100 ml). An adequate plasma level of 44 p.mol/liter (0.75 mg/100 ml) can be maintained by a daily supply of 60-75 mg ascorbic acid. The daily amount of ascorbic acid, which is catabolized by the human body, can be calculated to be 60 mg based on a total body pool of ascorbic acid of approximately 1500 mg and a maximum turnover rate of 4%. These data are the scientific basis for the formulation of the above recommendations to meet the physiological needs. Table IV shows the recommended daily vitamin C intake for different population groups from the different societies that issue such recommendations. 

About 3% of the body s vitamin C pool, which is 20-50 mg/kg body weight, is excreted in the urine as ascorbic acid, dehydroascorbic acid (a combined total of 25%) and their metabolites, 2,3-diketo-L-gulonic acid (20%) and oxalic acid (55%). An increase in excreted oxalic acid occurs only with a very high intake of ascorbic acid. Scurvy is caused by a dietary deficiency of ascorbic acid. 

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