Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Vitamin C Supplementation and Serum Uric Acid: A Meta-Analysis of Randomized Controlled Trials.

P. Juraschek,  Stephen, R. Miller,  Edgar, C. Gelber,  Allan

Background:

Vitamin C is an essential micronutrient with uricosuric properties. Observational studies demonstrate an inverse association between levels of dietary or plasma vitamin C and serum uric acid (SUA). Thus far, clinical trials of vitamin C report inconsistent effects on SUA. The purpose of this meta-analysis was to determine the pooled effect of vitamin C on SUA culled from prior reports.

Methods:

We conducted a meta-analysis of randomized controlled trials of vitamin C supplementation on SUA. A total of 1,988 publications, identified in MEDLINE, EMBASE, and CENTRAL databases, were subjected to the following inclusion criteria: (1) randomized controlled trials conducted on human subjects; (2) end-trial serum uric acid means and variance were reported; (3) oral vitamin C supplementation and a concurrent control group; and, (4) trial duration of at least one week. Trials that enrolled children or patients on dialysis or where vitamin C supplements were combined with other uricosuric agents were excluded. SUA effects were pooled by random-effects models and weighted by inverse variance.

Summary of Results:

Thirteen trials met our eligibility criteria, totaling 545 participants. The median dose of vitamin C was 500 mg/d, trial size ranged from 8 to 184 participants, and median study duration was 30 days. Eight trials examined vitamin C as the only active intervention, whereas 5 trials administered vitamin C together with other vitamins, minerals or pharmacologic agents. The aggregate weighted effect of the 13 trials showed a SUA reduction of -0.33 mg/dL (95% CI: -0.66, 0.00; P= 0.05). Trials with a mean pretreatment SUA level above 4.85 mg/dL, the median value for these 13 trials, had a significantly greater SUA reduction in comparison to trials with mean pretreatment values <=4.85 mg/dL (P= 0.02 in subgroup comparision). Notably, the pooled effects of trials with larger doses of vitamin C and those with vitamin C as the sole intervention showed greater significant reductions in SUA levels (Table).

Table. Vitamin C supplementation effects on serum uric acid - overall and subgroup analyses.

  Serum Uric Acid (mg/dL)
 nmean (95% CI)P-value
All Trials (N = 13)545-0.33 (-0.66, 0.00)0.05
Subgroup: Pretreatment Serum Uric Acid   
        Trials with mean UA<=4.85 mg/dL (N=5†)2040.15 (-0.09, 0.39)0.23
        Trials with mean UA>4.85 mg/dL (N=5†)252-0.83 (-1.62, -0.04)0.04
Subgroup: Vitamin C Dose   
        Trials with dose <500 mg/d (N = 6)2030.09 (-0.17, 0.34)0.52
        Trials with dose >=500 mg/d (N = 8*)369*-0.56 (-1.01, -0.11)0.01
Subgroup: Intervention   
        Only Vitamin C (N = 9*)372*-0.52 (-0.93, -0.10)0.02
        Vitamin C and other agents (N = 5)2000.12 (-0.15, 0.39)0.38
N = Number of trials; n = Number of trial participants.
† Total number does not equal 13 since 3 trials did not report mean pretreatment SUA.
* One trial consisted of two distinct vitamin C intervention groups.

Conclusions:

In this meta-analysis, vitamin C supplementation lowered SUA. Greater reductions in SUA occurred in trials that used high doses of vitamin C and in trials with subjects with higher pretreatment SUA levels. These data support consideration of vitamin C supplementation as a uricosuric agent in the prevention and control of gout.

To cite this abstract, please use the following information:
P. Juraschek, Stephen, R. Miller, Edgar, C. Gelber, Allan; Vitamin C Supplementation and Serum Uric Acid: A Meta-Analysis of Randomized Controlled Trials. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1574
DOI: 10.1002/art.29340

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