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Body Weight and Prior Depletion Affect Plasma Ascorbate Levels Attained on Identical Vitamin C Intake: A Controlled-Diet Study

National Cancer Institute (G.B., B.H.P., P.R.T.), Bethesda;
USDA Agricultural Research Center, Beltsville (A.R.M., O.A.L.), Maryland;
Our Lady of Mercy Medical Center, Bronx, New York (E.P.N.)

Address reprint requests to: Gladys Block, PhD, 426 Warren Hall, University of California, Berkeley, CA 94720.

Purpose: To evaluate the role of factors that may affect the level of plasma ascorbic acid (AA), including age, body weight, physical activity, minor illness and the impact of prior depletion and repletion.

Methods: After one month of stabilization on 60 mg vitamin C/day, subjects underwent two complete depletion-repletion cycles (one cycle=one month of vitamin C depletion with nine mg/day, followed by one month of repletion with 117 mg per day). Subjects (68 men, ages 30 to 59 years) did not smoke or drink alcohol during the study. All food was provided by the study.

Results: There was extreme individual variability in the plasma AA level achieved on an identical repletion dose: after four weeks at 117 mg/day of vitamin C, AA ranged from 26.8 µmol/L to 85.8 µmol/L. Body weight was inversely associated with plasma AA attained (p<0.0001). Regression analysis indicated that, compared to a 130-lb man, a 200-lb man reached 10 µmol/L lower AA after the first repletion and 18 µmol/L lower AA after the second repletion. One-third of the subjects did not reach a plasma plateau after the first repletion. Prior depletion and apparent repletion also had a major impact, and only 10% of subjects reached the same plasma AA on the second repletion as on the first repletion.

Conclusions: Plasma AA attained on a given dose depends on body weight (or dose per kg of body weight) and on whether or not any prior depletions had been repleted adequately. The results have implications for nutrition recommendations and research design.

Key words: ascorbic acid, vitamin C, nutrient requirements, obesity

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