Primary Outcome Measures:
- Time to first fall (or death)-recorded in months [ Time Frame: 24 months after randomization ]
Secondary Outcome Measures:
- Change in gait speed [ Time Frame: 2 years post-randomization ]
The public health burden of falls in older persons is substantial. Several lines of evidence suggest that vitamin D supplements might reduce the risk of falls, potentially by 25% or more in persons with low serum 25-hydroxyvitamin D [25(OH)D] levels. However, existing evidence is inconsistent and insufficient to guide policy. The trial is a seamless two-stage, Bayesian response-adaptive, randomized dose-finding trial designed to select the best dose of vitamin D supplementation and to potentially confirm the efficacy of that dose for fall prevention and other related outcomes. Participants will be community-dwelling adults, aged 70+ (goal of ~40% black, ~60% women), with a baseline serum 25(OH)D level of 10-29 ng/ml, who are at high risk for falling.
In Stage 1 of the adaptive design, participants will be randomly assigned to one of four vitamin D3 (cholecalciferol) doses: 200 IU/d, 1000 IU/d, 2000 IU/d, or 4000 IU/d, with assignment probabilities that will vary as falls are reported. Participants will take their assigned pills for two years, or until the study ends, whichever comes first. This stage of the design will select the best dose of vitamin D for prevention of falls, or confirm the futility of distinguishing any differences among the doses for fall prevention. If a best dose is selected, subsequent participants will be randomized in Stage 2 of the trial into the comparison (200 IU/d) or best dose group, and all participants (Stage 1 and Stage 2) will continue to be followed to potentially confirm efficacy. The investigators anticipate enrolling approximately 1,200 participants over the entire length of the project.
The primary outcome is time to first fall (or death) over two years of therapy. Next in importance is the outcome of gait speed. Other outcomes include fall rates, types of falls, balance, muscle strength, frailty, Short Physical Performance Battery (SPPB) score, 6-minute walk time, and physical activity assessed by accelerometry. Falls will be ascertained from fall calendars completed daily by participants and from self-report by phone. In-person follow-up visits will occur at 3, 12, and 24 months, with telephone visits occurring at 1, 6, 9, 15, 18, and 21 months after randomization. Subgroups with potential for greater benefit from vitamin D supplementation are blacks, those with baseline 25(OH)D of 10-19 ng/ml, and those with objective evidence of low physical function.
