Table 4.
Subgroup analyses comparing milk intake and hip fracture risk for case-control and cohort studies
| Cohort studies (n = 9) | Case-control studies (n = 7) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n | RR | 95% CI | I2 (%) | P a | P b | n | OR | 95% CI | I2 (%) | P a | P b | |
| Study quality | ||||||||||||
| Score ≥ 8 | 4 | 0.98 | 0.75–1.27 | 90.0 | <0.01 | 0.90 | 4 | 0.80 | 0.67–0.95 | 10.0 | 0.34 | 0.05 |
| Score < 8 | 4 | 1.03 | 0.86–1.24 | 0.0 | 0.82 | 3 | 0.42 | 0.25–0.71 | 35.0 | 0.21 | ||
| Region | ||||||||||||
| USA | 4 | 1.00 | 0.96–1.03 | 0.0 | 0.84 | 0.44 | 1 | 1.10 | 0.63–1.94 | NA | NA | 0.04 |
| Europe | 3 | 0.98 | 0.68–1.41 | 86.0 | <0.01 | 3 | 0.77 | 0.65–0.90 | 0.0 | 0.39 | ||
| Asia | 1 | 0.54 | 0.26–1.12 | 3 | 0.42 | 0.25–0.71 | 35.0 | 0.21 | ||||
| Sex | ||||||||||||
| Male | 5 | 0.91 | 0.70–1.19 | 48.0 | 0.10 | 0.68 | 1 | 0.82 | 0.61–1.11 | NA | NA | 0.28 |
| Female | 6 | 1.07 | 0.78–1.47 | 81.0 | <0.01 | 4 | 0.78 | 0.53–1.14 | 58.0 | 0.07 | ||
| Both | 3 | 0.91 | 0.70–1.18 | 23.8 | 0.23 | 2 | 0.46 | 0.25–0.85 | 44.0 | 0.18 | ||
| No. of cases | ||||||||||||
| ≥ 1000 | 2 | 1.19 | 0.85–1.66 | 90.0 | <0.01 | 0.16 | 1 | 0.71 | 0.58–0.87 | NA | NA | 0.21 |
| 100–1000 | 4 | 1.00 | 0.82–1.21 | 0.0 | 0.57 | 4 | 0.83 | 0.65–1.06 | 24.0 | 0.27 | ||
| ≤ 100 | 6 | 0.79 | 0.60–1.04 | 46.0 | 0.10 | 2 | 0.28 | 0.15–0.55 | 0.0 | 0.84 | ||
| Duration of follow-up years | ||||||||||||
| ≥ 10 years | 5 | 1.02 | 0.84–1.25 | 86.0 | <0.01 | 0.63 | NA | NA | NA | NA | NA | NA |
| < 10 years | 3 | 0.89 | 0.62–1.29 | 0.0 | 0.98 | NA | NA | NA | NA | NA | NA | |
| Age | ||||||||||||
| ≥ 70 | 4 | 1.00 | 0.96–1.03 | 0.0 | 0.80 | 0.45 | 3 | 0.61 | 0.34–1.09 | 68.0 | 0.04 | 0.66 |
| < 70 | 5 | 0.89 | 0.66–1.02 | 83.0 | <0.01 | 4 | 0.76 | 0.57–1.01 | 52.0 | 0.10 | ||
| Adjustment for confounders | ||||||||||||
| Smoking | ||||||||||||
| Yes | 5 | 1.06 | 0.87–1.29 | 85.0 | <0.01 | 0.21 | 2 | 0.87 | 0.67–1.12 | 0.0 | 0.50 | 0.32 |
| No | 3 | 0.78 | 0.55–1.11 | 0.0 | 0.52 | 5 | 0.60 | 0.42–0.88 | 60.0 | 0.04 | ||
| Alcohol | ||||||||||||
| Yes | 4 | 1.10 | 0.84–1.43 | 81.0 | <0.01 | 0.18 | 2 | 0.87 | 0.67–1.12 | 0.0 | 0.50 | 0.32 |
| No | 4 | 0.93 | 0.79–1.10 | 16.0 | 0.31 | 5 | 0.60 | 0.42–0.88 | 60.0 | 0.04 | ||
| BMI | ||||||||||||
| Yes | 5 | 1.00 | 0.77–1.29 | 79.0 | <0.01 | 0.71 | 4 | 0.80 | 0.67–0.95 | 10.0 | 0.34 | 0.05 |
| No | 3 | 0.99 | 0.96–1.03 | 0.0 | 0.83 | 3 | 0.42 | 0.25–0.71 | 35.0 | 0.21 | ||
| Physical activity | ||||||||||||
| Yes | 6 | 1.03 | 0.82–1.29 | 75.0 | <0.01 | 0.47 | 2 | 0.72 | 0.52–1.00 | 37.0 | 0.21 | 0.93 |
| No | 2 | 0.82 | 0.47–1.43 | 63.0 | 0.10 | 5 | 0.67 | 0.45–1.01 | 65.0 | 0.02 | ||
| Sunlight exposure | ||||||||||||
| Yes | 0 | NA | NA | NA | NA | NA | 2 | 0.74 | 0.63–0.88 | 0.0 | 0.43 | 0.67 |
| No | 8 | 1.01 | 0.84–1.20 | 80.0 | <0.01 | 5 | 0.62 | 0.38–1.01 | 67.0 | 0.02 | ||
| Total energy intake | ||||||||||||
| Yes | 5 | 1.11 | 0.91–1.35 | 86.0 | <0.01 | 0.05 | 0 | NA | NA | NA | NA | NA |
| No | 3 | 0.69 | 0.49–0.96 | 0.0 | 0.45 | 7 | 0.71 | 0.55–0.91 | 54.0 | 0.04 | ||
| Calcium and vitamin D supplementation | ||||||||||||
| Yes | 5 | 1.12 | 0.92–1.36 | 86.0 | <0.01 | 0.04 | 0 | NA | NA | NA | NA | NA |
| No | 3 | 0.69 | 0.50–0.95 | 0.0 | 0.47 | 7 | 0.71 | 0.55–0.91 | 54.0 | 0.04 | ||
Abbreviations: N, the number of studies; CI, confidence interval; OR, odds ratio; RR, relative risk; NA, not applicable; BMI, body mass index. Pa, heterogeneity within each subgroup; Pb, heterogeneity between subgroups with meta-regression analysis