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Plasma-Saturating Intakes of Vitamin C Confer Maximal Antioxidant Protection to Plasma

Department of Nutrition, Arizona State University East, Mesa, Arizona

Address reprint requests to: Carol Johnston, PhD, Department of Nutrition, Arizona State University East, 7001 E. Williams Field Rd, Mesa, AZ 85212. Email: carol.johnston{at}asu.edu.

Objective: Supplemental vitamin C has been shown to reduce oxidative damage in vivo, yet the dose-response relationship between vitamin C intake and antioxidant protection is not known. This report examined blood indicators of oxidative stress in subjects consuming graded doses of vitamin C, from 75 to 2000 mg/day.

Methods: Ten healthy, non-smoking men and women (26.1 ± 2.1 years) were recruited from a campus population. During the ten-week study, subjects limited fruit and vegetable consumption (3 servings/day) and consumed a multivitamin and mineral pill daily. Beginning at week 3, subjects ingested either a vitamin C (n = 8) or placebo (n = 2) capsule, which were identical in appearance and taste. The content of the vitamin C capsule increased every two weeks (from 250 mg at weeks 3–4 to 500 mg, 1000 mg, and 2000 mg at weeks 5–6, 7–8, 9–10, respectively). Fasting blood samples were collected at two-week intervals and analyzed for vitamin C, total lipid hydroperoxides and Heinz bodies in packed erythrocytes incubated 24 hours at 37°.

Results: Plasma vitamin C rose 55% in vitamin C-supplemented subjects by the end of the ten-week treatment (p < 0.05), and measures of oxidative stress decreased 60% to 90% (8.1 ± 0.6 to 3.5 ± 0.4 nmol/mL and 69.1 ± 7.8% to 6.7 ± 6.0% for total lipid hydroperoxides and Heinz bodies, respectively). Significant decreases in markers of oxidative stress were noted at the 500 mg, 1000 mg and 2000 mg dosages versus placebo. Antioxidant protection was similar at the 1000 mg and 2000 mg dosage.

Conclusions: These data indicate that the antioxidant protection afforded by short-term vitamin C supplementation is maximal at the 500–1000 mg dosage range.

Key words: vitamin C, oxidative stress, lipid peroxides, Heinz bodies

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