Table 1.
Baseline characteristics of eligible WHI calcium / vitamin D (CaD) trial participants.
| Covariate* | Placebo (N=17352) | Active treatment (N=17411) | P Value** |
|---|---|---|---|
| Age in years – median (interquartile range [IQR]) | 63 (58 – 69) | 63 (58 – 69) | 0.799 |
| Education | 0.950 | ||
| College or post-graduate degree – N (%) | 6320 (36.4) | 6339 (36.4) | |
| Some post-secondary education – N (%) | 6905 (39.8) | 6953 (39.9) | |
| High school or less – N (%) | 4127 (23.8) | 4119 (23.7) | |
| Race | 0.313 | ||
| Black – N (%) | 1538 (8.9) | 1576 (9.1) | |
| White – N (%) | 14545 (83.8) | 14496 (83.3) | |
| Other – N (%) | 1269 (7.3) | 1339 (7.7) | |
| Latitude | 0.960 | ||
| Southern (<35 degrees North) – N (%) | 5163 (29.8) | 5164 (29.7) | |
| Middle (35–40 degrees North) – N (%) | 4811 (27.7) | 4818 (27.7) | |
| Northern (>40 degrees North) – N (%) | 7378 (42.5) | 7429 (42.7) | |
| Hormone therapy trial treatment assignment | 0.421 | ||
| Not enrolled – N (%) | 9613 (55.4) | 9704 (55.7) | |
| Active treatment – N (%) | 3943 (22.7) | 3855 (22.1) | |
| Placebo – N (%) | 3796 (21.9) | 3852 (22.1) | |
| Diet modification trial treatment assignment | 0.466 | ||
| Not enrolled – N (%) | 5271 (30.4) | 5336 (30.6) | |
| Intervention – N (%) | 4650 (26.8) | 4564 (26.2) | |
| Control – N (%) | 7431 (42.8) | 7511 (43.1) | |
| Dietary vitamin D intake >50th percentile – N (%) | 8727 (50.3) | 8655 (49.7) | 0.276 |
| Taking non-study vitamin D supplements – N (%) | 4827 (27.8) | 4820 (27.7) | 0.780 |
| Body mass index (BMI; kg/m2) – median (IQR) | 28.0 (24.7 – 32.2) | 28.0 (24.7 – 32.1) | 0.176 |
| Current smoker – N (%) | 1310 (7.5) | 1352 (7.8) | 0.450 |
| Alcohol intake | 0.549 | ||
| Non-drinker – N (%) | 4917 (28.3) | 4885 (28.1) | |
| <1 drink/week – N (%) | 6063 (34.9) | 6181 (35.5) | |
| 1 or more drinks/week – N (%) | 6372 (36.7) | 6345 (36.4) | |
| Recreational physical activity >50th percentile – N (%) | 7842 (45.2) | 7927 (45.5) | 0.667 |
All variables were included as covariates in our Cox regression models with the following two exceptions. Recreational physical activity was missing for a substantial fraction of participants (8.8%), so it was included as a covariate only in the subgroup analysis where we stratified on recreational physical activity. Second, in our main analyses, we analyzed participants as they were randomized (intent-to-treat) and did not adjust for study medication adherence. Participants were stratified by adherence during the first year of follow-up in a subgroup analysis.
P values reflect the significance of the differences between treatment arms and are based on the Pearson chi-square and Wilcoxon rank sum tests for categorical and continuous covariates, respectively.