Study Overview
Objective. To test the effect of 12 months of vitamin D supplementation on lower-extremity power and function in older community-dwelling adults screened for low serum 25-hydroxyvitamin D (25(OH)D).
Design. A single-center, double-blind, randomized placebo-controlled study in which participants were assigned to 800 IU of vitamin D3 supplementation or placebo daily and were followed over a total period of 12 months.
Setting and participants. A total of 100 community-dwelling men and women aged ≥ 60 years with serum 25(OH)D ≤ 20 ng/mL at screening participated. Participants were prescreened by phone, and were excluded if they met any of the following exclusion criteria: vitamin D supplement use > 600 IU/day (for age 60-70 years) or > 800 IU/day (for age ≥ 71 years); vitamin D injection within the previous 3 months; > 2 falls or 1 fall with injury in past year; use of cane, walker, or other indoor walking aid; history of kidney stones within past 3 years; hypercalcemia (serum calcium > 10.8 mg/dL); renal dysfunction (glomerular filtration rate, < 30 mL/min); history of liver disease, sarcoidosis, lymphoma, dysphagia, or other gastrointestinal disorder; neuromuscular disorder affecting lower-extremity function; hip replacement within the past year; cancer treatment in the past 3 years; treatment with thiazide diuretics > 37.5 mg, teriparatide, denosumab, or bisphosphonates within the past 2 years; oral steroids (for > 3 weeks in the past 6 months); and use of fat malabsorption products or anticonvulsive therapy.
Main outcome measures. The primary outcome was leg extensor power assessed using a computer-interfaced bilateral Keiser pneumatic leg press. Secondary outcomes to measure physical function included: (1) backward tandem walk test (which is an indicator of balance and postural control during movement1); (2) Short Physical Performance Battery (SPPB) testing, which includes a balance assessment (ability to stand with feet positioned normally, semi-tandem, and tandem for 10s), a timed 4-m walk, and a chair stand test (time to complete 5 repeated chair stands); (3) stair climbing (ie, time to climb 10 steps, as a measure of knee extensor strength and functional capacity); and (4) handgrip strength (using a dynamometer). Lean tissue mass was assessed by dual X-ray absorptiometry (DEXA scan). Finally, other measures included serum total 25(OH)D levels measured at baseline, 4, 8, and 12 months, as well as 24-hour urine collection for urea-nitrogen and creatinine measurements.
Main results. Of the 2289 individuals screened for the study, 100 met eligibility criteria and underwent randomization to receive either 800 IU vitamin D supplementation daily (n = 49) or placebo (n = 51). Three patients (2 in vitamin D group and 1 in placebo group) were lost to follow up. The mean age of all participants was 69.6 ± 6.9 years. In the vitamin D group versus the control group, respectively, the percent male: female ratio was 66:34 versus 63:37, and percent Caucasian was 75% versus 82%. Mean body mass index was 28.2 ± 7.0 and mean serum 25(OH)D was 20.2 ± 6.7 ng/mL. At the end of the study (12 months), 70% of participants given vitamin D supplementation had 25(OH)D levels ≥ 30 ng/mL and all participants had levels ≥ 20 ng/mL. In the placebo group, the serum 25(OH)D level was ≥ 20 ng/mL in 54% and ≥ 30 ng/mL in 6%. The mean serum 25(OH)D level increased to 32.5 ± 5.1 ng/mL in the vitamin D–supplemented group, but no significant change was found in the placebo group (treatment × time, P < 0.001). Overall, the serum 1,25 (OH)2D3 levels did not differ between the 2 groups over the intervention period (time, P = 0.49; treatment × time, P = 0.27). Dietary intake of vitamin D, calcium, nitrogen, and protein did not differ or change over time between the 2 groups. The change in leg press power, function, and strength did not differ between the groups over 12 months (all treatment × time, P values ≥ 0.60). A total of 27 falls were reported (14 in vitamin D versus 9 in control group), of which 9 were associated with injuries. There was no significant change in lean body mass at the end of the study period in either group (treatment × time, P = 0.98).
Conclusion. In community-dwelling older adults with vitamin D deficiency (≤ 20 ng/mL), 12-month daily supplementation with 800 IU of vitamin D3 resulted in sufficient increases in serum 25(OH)D levels, but did not improve lower-extremity power, strength, or lean mass.
Commentary
Vitamin D deficiency is common in older adults (prevalence of about 41% in US adults ≥ 65 years old, according to Forrest et al2) and is likely due to dietary deficiency, reduced sun exposure (lifestyle), and decreased intestinal calcium absorption. As such, vitamin D deficiency has historically been a topic of debate and of interest in geriatric medicine, as it relates to muscle weakness, which in turn leads to increased susceptibility to falls.3 Interestingly, vitamin D receptors are expressed in human skeletal muscle,4 and in one study, 3-month supplementation of vitamin D led to an increase in type II skeletal muscle fibers in older women.5 Similarly, results from a meta-analysis of 5 randomized controlled trials (RCTs)6 showed that vitamin D supplementation may reduce fall risk in older adults by 22% (corrected odds ratio, 0.78; 95% confidence interval, 0.64-0.92). Thus, in keeping with this general theme of vitamin D supplementation yielding beneficial effects in clinical outcomes, clinicians have long accepted and practiced routine vitamin D supplementation in caring for older adults.