The effects of vitamin C supplementation on serum concentrations of uric acid: results of a randomized controlled trial.

OBJECTIVE: Reductions in serum uric acid levels are clinically relevant. Previous studies have suggested a uricosuric effect of vitamin C. Whether vitamin C reduces serum uric acid is unknown. We undertook this study to determine the effects of vitamin C supplementation on serum uric acid concentrations.

METHODS: The study was a double-blinded placebo-controlled randomized trial conducted in research units affiliated with an academic institution. Study participants were 184 nonsmokers, randomized to take either placebo or vitamin C supplements (500 mg/day) for 2 months.

RESULTS: At the end of the study period, serum uric acid levels were significantly reduced in the vitamin C group (mean change -0.5 mg/dl [95% confidence interval -0.6, -0.3]), but not in the placebo group (mean change 0.09 mg/dl [95% confidence interval -0.05, 0.2]) (P < 0.0001). The same pattern of results was evident in subgroups defined by age, sex, race, body mass index, chronic illness, diuretic use, and quartiles of baseline serum ascorbic acid levels. In the subgroups, from the lowest to the highest quartile of baseline serum uric acid, net mean changes (95% confidence intervals) in serum uric acid with vitamin C supplementation were -0.4 (-0.8, 0.01), -0.5 (-0.9, -0.2), -0.5 (-0.8, -0.2), and -1.0 (-1.6, -0.4) mg/dl (P = 0.06, 0.005, 0.003, and 0.002, respectively). Compared with placebo, vitamin C increased the estimated glomerular filtration rate.

CONCLUSION: Supplementation with 500 mg/day of vitamin C for 2 months reduces serum uric acid, suggesting that vitamin C might be beneficial in the prevention and management of gout and other urate-related diseases.