Effects of Vitamin D on Physical Function: Results From the STURDY Trial

Abstract

Background: Studies of the relationship between vitamin D and physical functioning have had inconsistent results.

Methods: Physical functioning measures were collected for up to 2 years during a 2-stage, Bayesian, response-adaptive, randomized trial of 4 doses of vitamin D3 supplementation (200 [control], 1 000, 2 000, and 4 000 IU/day) to prevent falls. Two community-based research units enrolled adults aged ≥70 years, with elevated fall risk and serum 25-hydroxyvitamin D level of 10-29 ng/mL. The Pooled Higher Doses (PHD) group (≥1 000 IU/day, n = 349) was compared to the control group (n = 339) on changes in Short Physical Performance Battery (SPPB) score and its component tests, Timed Up-and-Go (TUG) test, 6-minute walk distance, and grip strength.

Results: The trial enrolled 688 participants. Mean age was 77.2 years, 56.4% were male, 79.7% White, and 18.2% Black. While the PHD and control groups both lost function over time on most outcomes, the 2 groups did not show differential change overall on any outcome. Incidence of transitioning to poor functioning on gait speed, SPPB score, or TUG test did not differ by dose group.

Conclusion: In older persons with low serum 25-hydroxyvitamin D level and elevated fall risk, high-dose vitamin D supplementation, ≥1 000 IU/day, did not improve measures of physical function compared to 200 IU/day.

Clinical trial registration: NCT02166333.

Keywords: Physical functioning; Randomized controlled trial; Vitamin D.

Figure 1.

Box plots of serum 25(OH)D at entry and 3, 12, and 24 months after randomization in the primary analysis population. Pooled Higher Doses denotes the combined 1 000, 2 000, and 4 000 IU/day groups.

Figure 2.

Incident worsening in gait speed (A and B), SPPB score (C), and TUG time (D) in the primary analysis population. Each panel shows the percent of those with performance at least as good as the specified threshold level at baseline who worsen relative to the threshold during follow-up by dose (Pooled Higher Doses or 200 IU/day) and the Pooled Higher Doses versus 200 IU/day odds ratio (OR) of incident worsening by follow-up time. Participants whose baseline performance was worse than the specified threshold are excluded. The count below each bar is the number of participants in that dose group whose performance was at least as good as the threshold at baseline and who completed the measurement at the specified time point; the percent at the top of each bar is the percent of participants whose performance worsened at the specified time point. The Pooled Higher Doses versus 200 IU/day group OR of incident worsening for each time point is shown above each pair of bars with its 95% confidence interval (CI). The interaction p value shown on each plot tests whether the ORs differ over time. The Benjamini–Hochberg procedure was used to control the false discovery rate to less than 1/9 (1 out of the maximum number of overall comparisons in each family of analyses comparing dose groups; an adjusted p value is statistically significant if <.11). The ORs, 95% CIs, and p value are from a mixed-effects logistic regression model with the functional measure as the outcome and fixed effects including 1 term for treatment, 3 terms for time point, 3 treatment-by-time interaction terms, and a random intercept for each participant. Pooled Higher Doses denotes the combined 1 000, 2 000, and 4 000 IU/day groups. SPPB = Short Physical Performance Battery; TUG = Timed Up-and-Go test; IU = international units.