Table 2. Subgroup analysis of studies on the association of serum vitamin D status with the risk of MetS in observational studies.
| Study | No. of studies | OR or RR (95% Cl) | I2 (%) | P value for heterogeneity | P* | ||
|---|---|---|---|---|---|---|---|
| All studies | 23 | 0.81 (0.77–0.85) | 63.9 | 0.000 | |||
| Age | 0.475 | ||||||
| Total | 10 | 0.82 (0.74–0.91) | 73.5 | 0.000 | |||
| Middle | 4 | 0.81 (0.72–0.89) | 70.0 | 0.019 | |||
| Elderly | 9 | 0.80 (0.76–0.85) | 52.3 | 0.032 | |||
| Study design | 0.374 | ||||||
| Cross-sectional | 19 | 0.80 (0.76–0.84) | 53.5 | 0.003 | |||
| Cohort | 4 | 0.85 (0.72–0.98) | 85.8 | 0.000 | |||
| Study location | 0.290 | ||||||
| North America | 6 | 0.77 (0.70–0.84) | 43.7 | 0.114 | |||
| Asia-Pacific | 11 | 0.82 (0.75–0.90) | 74.0 | 0.000 | |||
| Europe | 6 | 0.83 (0.78–0.88) | 46.6 | 0.096 | |||
| MetS criteria | 0.840 | ||||||
| NCEP ATP-III | 11 | 0.81 (0.77–0.86) | 34.3 | 0.124 | |||
| Others | 12 | 0.81 (0.75–0.86) | 75.6 | 0.000 | |||
| Quality assessment | 0.010 | ||||||
| High (≥ 8) | 10 | 0.86 (0.81–0.92) | 55.2 | 0.017 | |||
| Low (< 8) | 13 | 0.77 (0.73–0.82) | 55.5 | 0.008 | |||
| Adjustment for confounders | |||||||
| Alcohol | 0.045 | ||||||
| Yes | 13 | 0.78 (0.74–0.82) | 34.3 | 0.108 | |||
| No | 10 | 0.84 (0.79–0.90) | 40.6 | 0.000 | |||
| Smoking | 0.798 | ||||||
| Yes | 17 | 0.82 (0.77–0.86) | 64.6 | 0.000 | |||
| No | 6 | 0.80 (0.74–0.87) | 68.5 | 0.007 | |||
| Physical activity | 0.500 | ||||||
| Yes | 17 | 0.82 (0.78–0.87) | 70.3 | 0.000 | |||
| No | 6 | 0.83 (0.73–0.93) | 77.9 | 0.000 | |||
| Education | 0.626 | ||||||
| Yes | 9 | 0.82 (0.77–0.87) | 63.9 | 0.005 | |||
| No | 14 | 0.80 (0.74–0.86) | 66.1 | 0.000 | |||
| BMI | 0.477 | ||||||
| Yes | 9 | 0.82 (0.72–0.91) | 74.3 | 0.000 | |||
| No | 14 | 0.80 (0.77–0.84) | 53.9 | 0.009 | |||
| Energy intake | 0.640 | ||||||
| Yes | 3 | 0.79 (0.70–0.88) | 47.0 | 0.152 | |||
| No | 20 | 0.81 (0.77–0.86) | 66.3 | 0.000 | |||
| Calcium (dietary intake or supplement use) | 0.442 | ||||||
| Yes | 5 | 0.79 (0.73–0.85) | 37.2 | 0.173 | |||
| No | 18 | 0.82 (0.77–0.87) | 68.4 | 0.000 | |||
| Vitamin D (dietary intake or supplement use) | 0.480 | ||||||
| Yes | 3 | 0.77 (0.67–0.88) | 28.0 | 0.249 | |||
| No | 20 | 0.82 (0.78–0.86) | 67.1 | 0.000 | |||
| Serum PTH | 0.782 | ||||||
| Yes | 3 | 0.81 (0.73–0.89) | 0.0 | 0.534 | |||
| No | 20 | 0.81 (0.77–0.85) | 68.1 | 0.000 | |||
| Season | 0.536 | ||||||
| Yes | 9 | 0.80 (0.74–0.86) | 57.1 | 0.017 | |||
| No | 14 | 0.82 (0.77–0.87) | 69.2 | 0.000 | |||
MetS, metabolic syndrome; OR, odds ratio; RR, relative risk; CI, confidence interval; NCEP ATP-III, National Cholesterol Education Program Adult Treatment Panel III; BMI, body mass index; PTH, parathyroid hormone.
*P values for heterogeneity between subgroups in meta-regression analysis.