Table 2.
Subgroup analyses consisting of the pooled effect sizes of vitamin C supplementation on serum uric acid level, stratified by trial and subject characteristics.
| Change in serum uric acid (mg/dL) | ||||||
|---|---|---|---|---|---|---|
| Sub-group | N§ | Effect | 95% CI | I2 | P* | |
| LL | UL | |||||
| Dose | ||||||
| <500 mg/d | 6 | 0.02 | -0.21 | 0.26 | 0.0% | 0.10 |
| ≥500 mg/d | 8 | -0.59 | -1.05 | -0.13 | 79.9% | |
| Duration | ||||||
| <30 days | 7 | -0.49 | -1.20 | 0.22 | 85.2% | 0.52 |
| ≥30 days | 7 | -0.25 | -0.56 | 0.06 | 63.0% | |
| Baseline Serum Ascorbic Acid | ||||||
| <56.2 μmol/L | 3 | -0.02 | -0.30 | 0.27 | 0.0% | 0.20 |
| ≥56.2 μmol/L | 4 | -0.33 | -0.75 | 0.09 | 53.7% | |
| Mean Age | ||||||
| <47.7 | 6 | -0.53 | -1.32 | 0.27 | 85.3% | 0.55 |
| ≥47.7 | 7 | -0.29 | -0.61 | 0.04 | 66.1% | |
| %Male | ||||||
| <53 | 6 | -0.26 | -0.59 | 0.07 | 58.5% | 0.66 |
| ≥53 | 7 | -0.41 | -1.06 | 0.24 | 85.6% | |
| Baseline Serum Uric Acid | ||||||
| <4.85 mg/dL | 5 | 0.13 | -0.12 | 0.37 | 0.0% | 0.03 |
| ≥4.85 mg/dL | 5 | -0.78 | -1.46 | -0.09 | 85.0% | |
| Trial Design | ||||||
| Parallel | 10 | -0.37 | -0.80 | 0.07 | 83.8% | 0.91 |
| Crossover | 4 | -0.31 | -0.63 | 0.02 | 0.0% | |
| Vit C Only Intervention | ||||||
| Yes | 9 | -0.54 | -0.96 | -0.11 | 78.1% | 0.16 |
| No | 5 | 0.04 | -0.20 | 0.29 | 0.0% | |
| Placebo Use | ||||||
| Yes | 10 | -0.59 | -0.95 | -0.24 | 71.2% | 0.01 |
| No | 4 | 0.19 | -0.07 | 0.45 | 0.0% | |
| Allocation Concealment | ||||||
| Yes | 4 | -0.31 | -0.75 | 0.13 | 76.5% | 0.89 |
| Not Reported | 10 | -0.37 | -0.86 | 0.11 | 79.1% | |
| Double-blind Design | ||||||
| Yes | 9 | -0.50 | -0.66 | -0.35 | 0.0% | 0.75 |
| No | 5 | -0.30 | -1.17 | 0.58 | 90.8% | |
| Trial Reported Compliance | ||||||
| Yes | 5 | -0.35 | -0.75 | 0.05 | 71.1% | 0.92 |
| No | 9 | -0.34 | -0.87 | 0.18 | 0.0% | |
| Healthy Trial Population | ||||||
| Yes | 7 | -0.60 | -1.26 | 0.06 | 82.5% | 0.20 |
| No | 7 | -0.15 | -0.49 | 0.20 | 71.1% | |
| Trial Size | ||||||
| <29 | 5 | -0.58 | -1.58 | 0.41 | 87.9% | 0.37 |
| ≥29 | 9 | -0.23 | -0.51 | 0.05 | 63.4% | |
*
P-values represent comparison of effects between subgroups. Category bounds were determined by the median of abstracted values.
§
N represents the number of trials. The number of trials may not always add to 13 due to the treatment of one trial as two groups (Kyllastinen et al, 1990) and due to the varying availability of subgroup data in each trial.