Table 2.
Subgroup analysis for standard mean difference (SMD) of dietary vitamin C level in MetS vs. control subjects.
| Stratification | Number of studies | Pooled SMD | 95% CI | P-value | Heterogeneity |
|---|---|---|---|---|---|
| All studies | 21 | −0.04 | −0.08, −0.01 | P = 0.02 | P < 0.001; I2 = 69% |
| Diagnostic criteria of MetS | |||||
| NCEP ATP III | 13 | −0.06 | −0.11, −0.01 | P = 0.01 | P < 0.001; I2 = 72% |
| Other | 8 | −0.01 | −0.03, 0.02 | P = 0.65 | P = 0.07; I2 = 45% |
| Geographical region | |||||
| Asia | 14 | −0.03 | −0.08, 0.01 | P = 0.16 | P < 0.001; I2 = 74% |
| Non-Asia | 7 | −0.07 | −0.14, 0.00 | P = 0.06 | P = 0.04; I2 = 51% |
| Sample size | |||||
| <1,000 | 11 | −0.07 | −0.19, 0.05 | P = 0.23 | P < 0.001; I2 = 73% |
| >1,000 | 10 | −0.03 | −0.07, 0.00 | P = 0.05 | P < 0.001; I2 = 66% |
| Exposure assessment | |||||
| FFQ | 3 | 0.00 | −0.04, 0.04 | P = 0.95 | P = 0.40; I2 = 0% |
| 24 h or 3 days recall | 17 | −0.04 | −0.08, 0.00 | P = 0.05 | P < 0.001; I2 = 69% |
| Study quality | |||||
| High-quality | 16 | −0.04 | −0.07, −0.01 | P = 0.02 | P < 0.001; I2 = 57% |
| Low-quality | 5 | −0.11 | −0.36, 0.13 | P = 0.38 | P < 0.001; I2 = 87% |