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Original Research Communication |
1 From the Centre de Recherche sur le Vieillissement, Institut Universitaire de Gériatrie de Sherbrooke (KJL, HT, ATS, HP, and JRW), and the Unité de Recherche Pulmonaire, Hospitalier Universitaire de Sherbrooke (AMC), Canada.
Background: Ascorbate and glutathione play central roles in the defense against free radicals and oxidants that are implicated in chronic diseases.
Objective: The objective was to determine the ability of vitamin C supplements to modulate the concentration of glutathione in human lymphocytes.
Design: The effect of vitamin C supplements was determined in a sequential study with time points before supplementation, after 13 wk of vitamin C supplements (500 or 1000 mg/d), and after 13 wk of matching placebo. The supplementation group was selected on the basis of low plasma ascorbate (<33 mmol/L) and consisted of 48 healthy men and women, smokers and nonsmokers, aged 25–64 y. Ascorbate and glutathione were measured in purified lymphocytes.
Results: At baseline, the mean (±SD) concentration of plasma ascorbate was 19.5 ± 7.2 µmol/L, 22.5 µmol/L below the median of normal distribution. The ascorbate concentration in plasma was linearly associated with that in lymphocytes (r = 0.53, P < 0.001). On supplementation with vitamin C, lymphocyte ascorbate increased by 51% (from 16.7 ± 4.9 to 25.3 ± 6.9 nmol/mg protein; P < 0.001) and was accompanied by an increase of lymphocyte glutathione by 18% (from 22.5 ± 4.5 to 26.6 ± 6.5 nmol/mg protein; P < 0.001). After placebo, the ascorbate and glutathione concentrations fell to near baseline concentrations (17.1 ± 5.4 and 23.5 ± 6.4 nmol/mg protein, respectively). No significant interaction was observed for sex and smoking status. Finally, the changes in lymphocyte ascorbate after supplementation were strongly associated with changes in lymphocyte glutathione (r = 0.71, P < 0.001). The association suggests that every 1-mol change in ascorbate is accompanied by a change of 
0.5 mol in glutathione.
Conclusion: Vitamin C supplements increase glutathione in human lymphocytes.
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