Table 1 shows number of cases for each clinical outcome and age-adjusted incidence rates for both cohorts according to randomization assignment in the CT and according to baseline use of calcium and vitamin D supplements in the OS. Incidence rates for most outcomes differed little between randomized groups in the CT.
Table 2 provides HR estimates for fracture, and death according to years from CaD initiation, both for the CT as a whole and for the trial subset not using personal calcium or vitamin D at baseline; for the OS with outcome-specific confounding control; and for the combined CT and OS, with CT component including either the entire trial cohort or the subset not using personal supplements.
In women not taking supplements at baseline, the HR for hip fracture in the CT following 5 or more years of CaD supplementation versus placebo was 0.62 (95 % CI, 0.38 to 1.00). In combined analyses of CT and OS data (with residual confounding provision in the OS), the corresponding HR was 0.65 (95 % CI, 0.44 to 0.98) with evidence (P = 0.02) of HR trend with time from calcium and vitamin D initiation. Thus, there was evidence for lower hip fracture rates following some years of calcium plus vitamin D use in the subset of women not taking personal calcium or vitamin D supplements. This risk reduction was suggestive, but not clearly evident in the trial cohort as a whole (HR 0.82; 95 % CI, 0.61 to 1.12), or in combined trial and OS analyses. These combined overall CT and OS analyses provide some evidence for hip fracture benefit in the 5 or more years category (HR 0.78; 95 % CI, 0.59 to 1.03). Total fracture showed little evidence for association with CaD supplementation, with HRs from the OS tending to be larger than those from the CT.
To help interpret the hip fracture HRs, it can be noted that the FFQ 5th, 25th, 50th, 75th, and 95th percentiles for dietary calcium (milligram per day) were 291, 512, 738, 1,043, and 1,650, and for dietary vitamin D (IU/day), and were 47, 96, 149, 221, and 397 in the CT. Corresponding percentiles in the OS were 291, 571, 748, 1,074, and 1,693 for calcium, and 43, 93, 147, 225, and 407 for vitamin D, very similar to those in the CT. It is evident that personal supplement use of 500 mg/day or more calcium and 400 IU/day or more of vitamin D contributes a substantial fraction to the total consumption of these nutrients in study cohorts.
Table 2 also shows that total mortality was somewhat reduced in the first 2 years from randomization among women assigned to active treatment in the CT. This pattern was not evident in later years of follow-up, in corresponding OS analyses, or in combined CT and OS analyses.
Table 3 provides corresponding analyses for cardiovascular diseases. There was little evidence for an adverse influence of CaD supplementation on the risk for MI, CHD, total heart disease, stroke, or total cardiovascular disease, from either the CT or OS, or from their combined analysis. In fact, the OS data alone suggest a reduction in total heart disease risk and total cardiovascular disease risk among supplement users.
Table 4 presents corresponding analyses for invasive cancer. Among women with no personal supplements at baseline, there was some evidence for a reduction in breast cancer risk (HR 0.80; 95 % CI, 0.66 to 0.96, P = 0.02) and total cancer risk (HR 0.88, 95 % CI, 0.78 to 0.98, P = 0.03), with little suggestion of HR time trend and with no support from OS data. These patterns were similar in the trial cohort as a whole, but far from significant.
Table 5 presents HRs from the OS for calcium-only and for vitamin D-only supplementation. HRs for calcium plus vitamin D are also repeated from earlier tables for comparative purposes. As mentioned previously, these HRs are subject to residual confounding and other biases, but comparative HRs across supplement types presumably less so. Significant associations were not found for hip fracture or for total fracture for either supplement alone or combined. No associations of calcium or vitamin D with incidence for the specific cancer sites considered or for total invasive cancer were suggested by these Table 5 analyses. A non-significant early elevation in MI incidence with vitamin D is not precisely estimated and is not apparent with the combination of calcium and vitamin D. HR estimates were below one (P < 0.05) for calcium alone in relation to MI and CHD, and as previously mentioned, for CaD in relation to total heart disease.
Data on adherence to assigned supplement category is important for the interpretation of Table 5 analyses. Following the baseline assessment, data on supplement use in the OS was collected only in conjunction with a clinic visit 3 years later. Of the OS women using calcium plus vitamin D at baseline, a substantial 80.9 % reported continued use 3 years later, with 10.9 % stopping use of both of these supplements, 6.9 % moving to calcium-only, and 1.4 % moving to vitamin D-only supplements. In contrast among baseline calcium-only users, a remarkable 57.1 % had moved to CaD preparations by 3 years later, with only 23.7 % still using calcium only, and 17.6 % had stopped using either supplement. Similarly 56.5 % of baseline vitamin D users had moved to CaD by 3 years later, with only 16.4 % still using vitamin D only. Equally impressive, only 49.9 % of baseline non-users of these supplements retained that status 3 years later, with 38.7 % becoming CaD users. It is evident that the contrasts presented in Table 5 primarily pertain to CaD use, and even then the non-user control group evidently becomes quite contaminated over the follow-up period.
Table 6 shows HR estimates from the CT using follow-up data from each participating woman only during the period of time that she remained adherent to her assigned active CaD or placebo pills. Among adherent women, hip fracture risk was lower in the active treatment group both in the overall trial cohort (P = 0.05), and in the subset of women without personal supplements (P = 0.04). The HR (95 % CI) among adherent women not using personal supplements was an impressive 0.24 (0.07, 0.84) following 5 or more years of use among women not using personal supplements. The myocardial infarction HR (95 % CI) was a non-significant 1.18 (0.88, 1.59) among women not using personal calcium or vitamin D. In contrast, breast and total invasive cancer risks were reduced (both P = 0.01) among women adherent to CaD in these analyses. Analyses that incorporated inverse adherence probability weights were similar with overall test P values among women not using personal supplements of 0.02 for hip fracture, 0.98 for MI, 0.06 for invasive breast cancer, and 0.01 for total invasive cancer.
For completeness, corresponding analyses were also carried out for the complementary subset of 20,275 CT women who reported taking personal supplements of calcium or vitamin D, or both, at the time of WHI enrollment. Overall, HRs (95 % CI) in this subset were as follows: hip fracture 0.90 (0.69,1.17), total fracture 0.95 (0.87,1.02), MI 0.97 (0.80,1.17), CHD 1.01 (0.85,1.20), total heart disease 1.04 (0.94,1.16), stroke 0.83 (0.67,1.01), total cardiovascular disease 0.99 (0.90,1.08), colorectal cancer 1.32 (0.98, 1.79), breast cancer 1.09 (0.93,1.28), total invasive cancer 1.04 (0.94,1.15), and death 0.91 (0.79,1.04). None of these HRs differ significantly from unity, though for some outcomes, there is a significant HR difference between the personal supplements and no personal supplements subsets, including stroke (P = 0.04), colorectal cancer (P = 0.04), breast cancer (P = 0.01), and total invasive cancer (P = 0.03).
Among women who were adherent to study pills, the overall HRs (95 % CIs) in the personal supplements user subset were as follows: hip fracture 0.85 (0.58,1.24), total fracture 0.97 (0.87,1.07), MI 0.96 (0.74,1.26), CHD 1.00 (0.79,1.28), total heart disease 1.05 (0.91,1.21), stroke 0.81 (0.60,1.08), total cardiovascular disease 1.01 (0.89,1.14), colorectal cancer 1.17 (0.78,1.73), breast cancer 1.04 (0.85,1.29), total invasive cancer 1.02 (0.90,1.17), and death 0.91 (0.74,1.11). There was significant adherent HR variation between the personal supplements and no personal supplements subsets only for breast cancer (P = 0.03) and total invasive cancer (P = 0.03) in these adherence-adjusted analyses.
Concerning urinary tract stones, as previously reported [1, 7] 449 women (0.35 %) in the group randomized to CaD and 381 women (0.30 %) in the placebo group developed urinary tract stones during the trial intervention period, leading to an HR (95 % CI) of 1.17 (1.02, 1.34). Among adherent women, the HR (95 % CI) was 1.21 (0.98, 1.50). These analyses were repeated here, separately for the no personal supplements and personal supplements groups.
In the no personal supplements subset, the HR (95 % CI) was 1.08 (0.88,1.32) based on 199 women developing urinary tract stones in the active treatment group and 180 in the placebo group. The corresponding HR (95 % CI) in the personal supplements subset was 1.23 (1.01, 1.48) based on 239 and 197 women with stones in the active and placebo groups. The HRs did not differ significantly (P = 0.39) between the two subsets. Among adherent women, the HR (95 % CI) was 1.21 (0.87, 1.69) in the no personal supplements group and 1.19 (0.89, 1.58) in the personal supplements group, with no evidence (P = 0.87) for difference between the HRs for adherent women between the two subsets.
Subset analyses by age group or by prior CVD history were generally similar to those for the overall cohorts for the various outcomes considered above and are not shown.