Table 2. Subgroup Analysis of Association Between Calcium Supplementation and Fracture Incidence for Each Variable.
| Variable | No. of Trials | No. of Participants | Fracture, RR (95% CI) | P Valuea | |
|---|---|---|---|---|---|
| With Fracture | Total | ||||
| Hip Fracture (Primary Outcome) | |||||
| Calcium dose, g/d | |||||
| ≥1 | 5 | 117 | 5243 | 1.55 (0.79-3.05) | .79 |
| <1 | 1 | 17 | 1460 | 1.83 (0.68-4.93) | |
| Sex | |||||
| Women-only trials | 3 | 41 | 3066 | 1.97 (0.74-5.28) | .39 |
| Trials with men and women | 3 | 93 | 3637 | 1.23 (0.83-1.84) | |
| Previous fractures | |||||
| Yes | 2 | 92 | 2707 | 1.21 (0.81-1.82) | .18 |
| Otherb | 4 | 42 | 3996 | 2.17 (1.02-4.62) | |
| Calcium intake, mg/d | |||||
| ≥900 | 1 | 17 | 1460 | 1.83 (0.68-4.93) | .99 |
| <900 | 3 | 25 | 2536 | 1.86 (0.38-9.14) | |
| Baseline 25OHD, ng/mL | |||||
| ≥20 | 3 | 41 | 3066 | 1.97 (0.74-5.28) | .37 |
| <20 | 1 | 90 | 2643 | 1.21 (0.81-1.83) | |
| Nonvertebral Fracture | |||||
| Calcium dose, g/d | |||||
| ≥1 | 5 | 595 | 4549 | 0.95 (0.82-1.10) | .61 |
| <1 | 1 | 21 | 261 | 1.18 (0.52-2.68) | |
| Sex | |||||
| Women-only trials | 3 | 247 | 1842 | 0.96 (0.76-1.21) | .96 |
| Trials with men and women | 3 | 369 | 2968 | 0.95 (0.79-1.15) | |
| Previous fractures | |||||
| Yes | 2 | 348 | 2707 | 0.94 (0.77-1.14) | .82 |
| Otherb | 4 | 268 | 2103 | 0.97 (0.78-1.22) | |
| Calcium intake, mg/d | |||||
| ≥900 | 0 | 0 | 0 | Not estimable | NA |
| <900 | 4 | 268 | 2103 | 0.97 (0.78-1.22) | |
| Baseline 25OHD, ng/mL | |||||
| ≥20 | 4 | 268 | 2103 | 0.97 (0.78-1.22) | .76 |
| <20 | 1 | 341 | 2643 | 0.93 (0.76-1.13) | |
| Vertebral Fracture | |||||
| Calcium dose, g/d | |||||
| ≥1 | 7 | 151 | 4796 | 0.81 (0.60-1.08) | .78 |
| <1 | 2 | 97 | 1721 | 0.87 (0.57-1.33) | |
| Sex | |||||
| Women-only trials | 6 | 223 | 3549 | 0.85 (0.66-1.08) | .64 |
| Trials with men and women | 3 | 25 | 2968 | 0.69 (0.31-1.54) | |
| Previous fractures | |||||
| Yes | 3 | 7 | 2757 | 1.34 (0.29-6.15) | .54 |
| Otherb | 6 | 241 | 3760 | 0.82 (0.65-1.05) | |
| Calcium intake, mg/d | |||||
| ≥900 | 1 | 77 | 1460 | 0.97 (0.63-1.51) | .37 |
| <900 | 5 | 164 | 2300 | 0.77 (0.58-1.02) | |
| Baseline 25OHD, ng/mL | |||||
| ≥20 | 6 | 241 | 3760 | 0.82 (0.65-1.05) | .26 |
| <20 | 1 | 4 | 2643 | 3.05 (0.32-29.26) | |
| Total Fractures | |||||
| Calcium dose, g/d | |||||
| ≥1 | 6 | 665 | 5327 | 0.85 (0.67-1.09) | .90 |
| <1 | 1 | 236 | 1460 | 0.87 (0.69-1.10) | |
| Sex | |||||
| Women-only trials | 3 | 526 | 3066 | 0.88 (0.74-1.06) | .51 |
| Trials with men and women | 4 | 375 | 3721 | 0.71 (0.37-1.35) | |
| Previous fractures | |||||
| Yes | 2 | 353 | 2707 | 0.95 (0.78-1.15) | .31 |
| Otherb | 5 | 548 | 4080 | 0.79 (0.60-1.06) | |
| Calcium intake, mg/d | |||||
| ≥900 | 1 | 236 | 1460 | 0.87 (0.69-1.10) | .27 |
| <900 | 3 | 308 | 2536 | 0.50 (0.20-1.30) | |
| Baseline 25OHD, ng/mL | |||||
| ≥20 | 3 | 526 | 3066 | 0.88 (0.74-1.06) | .64 |
| <20 | 1 | 345 | 2643 | 0.94 (0.77-1.15) | |
Abbreviations: RR, relative risk; 25OHD, 25-hydroxyvitamin D.
a
P value for heterogeneity between subgroups.
b
Includes previous no fracture, partial fracture, and missing fracture data.