TABLE 3.
Hazard ratios of total fracture by vitamin D and calcium intakes among postmenopausal women in the Women's Health Initiative Observational Study1
| Vitamin A |
Retinol |
|||||
| Strata | n | Mean vitamin A2 | Multivariate HR (95% CI)3 | n | Mean retinol2 | Multivariate HR (95% CI)3 |
| μg RE/d | μg/d | |||||
| Lower vitamin D intake (≤11 μg/d) | P for trend: 0.022 | P for trend: 0.056 | ||||
| Quintile 1 | 14,199 | 4445 | 1.00 | 14,770 | 348 | 1.00 |
| Quintile 2 | 10,906 | 5430 | 1.02 (0.94, 1.10) | 13,424 | 609 | 1.02 (0.95, 1.10) |
| Quintile 3 | 7575 | 6162 | 1.10 (1.00, 1.20) | 7484 | 894 | 1.05 (0.97, 1.15) |
| Quintile 4 | 4773 | 6944 | 1.11 (0.99, 1.24) | 2321 | 1219 | 1.09 (0.96, 1.23) |
| Quintile 5 | 2966 | 8902 | 1.19 (1.04, 1.37) | 2420 | 2488 | 1.15 (1.03, 1.29) |
| Higher vitamin D intake (>11 μg/d) | P for trend: 0.678 | P for trend: 0.521 | ||||
| Quintile 1 | 950 | 4710 | 1.00 | 379 | 370 | 1.00 |
| Quintile 2 | 4243 | 5507 | 0.99 (0.81, 1.19) | 1725 | 664 | 1.07 (0.79, 1.44) |
| Quintile 3 | 7575 | 6205 | 0.93 (0.78, 1.12) | 7666 | 967 | 1.00 (0.75, 1.32) |
| Quintile 4 | 10,376 | 7007 | 0.93 (0.77, 1.12) | 12,828 | 1246 | 1.00 (0.75, 1.31) |
| Quintile 5 | 12,184 | 8957 | 0.87 (0.72, 1.06) | 12,730 | 2123 | 0.95 (0.72, 1.25) |
| Lower calcium intake (≤1236 mg/d) | P for trend: 0.446 | P for trend: 0.490 | ||||
| Quintile 1 | 12,954 | 4442 | 1.00 | 12,796 | 343 | 1.00 |
| Quintile 2 | 10,959 | 5441 | 1.01 (0.94, 1.09) | 10,820 | 612 | 0.99 (0.92, 1.08) |
| Quintile 3 | 8708 | 6170 | 1.03 (0.94, 1.12) | 7923 | 930 | 1.05 (0.97, 1.14) |
| Quintile 4 | 6389 | 6951 | 1.06 (0.96, 1.18) | 5975 | 1231 | 1.06 (0.97, 1.16) |
| Quintile 5 | 3270 | 8727 | 1.02 (0.90, 1.16) | 4766 | 2196 | 1.00 (0.91, 1.10) |
| Higher calcium intake (>1236 mg/d) | P for trend: 0.080 | P for trend: 0.207 | ||||
| Quintile 1 | 2195 | 4577 | 1.00 | 2353 | 374 | 1.00 |
| Quintile 2 | 4190 | 5481 | 1.04 (0.91, 1.20) | 4329 | 622 | 1.15 (1.01, 1.32) |
| Quintile 3 | 6442 | 6201 | 1.07 (0.94, 1.22) | 7227 | 932 | 1.10 (0.96, 1.25) |
| Quintile 4 | 8760 | 7014 | 1.04 (0.91, 1.19) | 9174 | 1248 | 1.13 (0.99, 1.29) |
| Quintile 5 | 11,880 | 8982 | 1.03 (0.89, 1.18) | 10,384 | 2175 | 1.11 (0.96, 1.25) |
| Lower vitamin D and calcium intakes | P for trend: 0.313 | P for trend: 0.258 | ||||
| Quintile 1 | 12,393 | 4430 | 1.00 | 12,659 | 343 | 1.00 |
| Quintile 2 | 8532 | 5425 | 1.00 (0.92, 1.10) | 10,044 | 607 | 0.98 (0.90, 1.07) |
| Quintile 3 | 5253 | 6153 | 1.02 (0.91, 1.14) | 4515 | 896 | 1.01 (0.91, 1.12) |
| Quintile 4 | 2803 | 6918 | 1.06 (0.91, 1.23) | 1474 | 1216 | 1.06 (0.91, 1.23) |
| Quintile 5 | 1095 | 8886 | 1.18 (0.98, 1.41) | 1384 | 2498 | 1.17 (1.01, 1.36) |
| Higher vitamin D and calcium intakes | P for trend: 0.393 | P for trend: 0.671 | ||||
| Quintile 1 | 389 | 4707 | 1.00 | 242 | 380 | 1.00 |
| Quintile 2 | 1816 | 5521 | 1.20 (0.82, 1.48) | 949 | 654 | 1.16 (0.80, 1.69) |
| Quintile 3 | 4120 | 6212 | 1.01 (0.76, 1.34) | 4258 | 961 | 1.02 (0.72, 1.44) |
| Quintile 4 | 6790 | 7024 | 1.00 (0.76, 1.33) | 8327 | 1251 | 1.05 (0.74, 1.48) |
| Quintile 5 | 10,009 | 9025 | 0.95 (0.71, 1.27) | 9348 | 2141 | 1.02 (0.72, 1.43) |
The cutoffs for the vitamin D and calcium stratification were selected based on the mean of each nutrient in the study population. HR, hazard ratio; RE, retinol equivalent.
The interactions of vitamin A and retinol with calcium were significant (P = 0.001 in both analyses); however, the interactions were not significant with vitamin D. Only when the interaction term was analyzed as categorical was the highest intake of retinol with vitamin D significant (P = 0.033 for the subgroup analysis).
Risk estimates were adjusted for age; energy, vitamin K, protein, alcohol, and caffeine intakes; smoking; BMI; HR therapy use; total METs per week; ethnic group; and region.