A Randomized Controlled Trial of the Effects of Vitamin D on Muscle Strength and Mobility in Older Women with Vitamin D Insufficiency

Kun Zhu, PhD; Nicole Austin, PhD; Amanda Devine, PhD; David Bruce, MD; Richard L. Prince, MD

Disclosures

J Am Geriatr Soc. 2010;58(11):2063-2068. 

In This Article

Results

Recruitment, Retention, and Compliance

Three thousand six hundred ninety-eight subjects responded to letters asking them to join the study and were contacted by telephone; of these, 827 attended a clinic screening visit, and of these, 302 who met the inclusion criteria entered the study (Figure 1). Participant withdrawals were not significantly different between the two groups. Excluding the 14 subjects who did not have 12-month muscle strength and mobility measured, results on 129 and 132 patients in the vitamin D and control groups were used for this study (Figure 1). Medication discontinuations after recruitment were not significantly different between the two groups (Figure 1). There was no significant difference between the vitamin D group and the control group in adherence rate to study medication in subjects who remained on medication as determined from tablet counting (86.7% and 86.8%, respectively).

Figure 1.

Participant flow through the study.

Participant Characteristics

There were no significant differences between the vitamin D and control groups in any baseline characteristics listed in Table 1 and Table 2 . The majority (96.6%) of subjects were Caucasian, more than 80% rated their fitness as average for age or above, and 16.5% needed to use a walking aid. The mean baseline calcium intake was 1,087±456 mg/d.

Effects on Vitamin D Status

Mean baseline 25(OH)D concentration was 17.7±4.2 ng/mL, with no significant difference between the two groups. Sixty-six percent of subjects had baseline 25(OH)D concentrations below 20 ng/mL. At 12 months, the vitamin D group had significantly higher serum 25(OH)D concentrations than the control group (Table 2). In the vitamin D group, at 12 months, 79% of subjects had 25(OH)D levels greater than 20 ng/mL, and 47% had 25(OH)D level greater than 24 ng/mL.

Effects on Muscle Strength and Mobility Function

Over the 12-month study, there was significant improvement in knee flexor strength and all hip muscle strength and mobility as measured using the TUAG in both groups. Ankle dorsiflexion strength reduced significantly in both groups, and there was no change in knee extensor strength after 12 months (Table 2).

Because there was no between-group treatment effect on the averages of these variables, interactions between treatment group and baseline muscle strength and mobility were investigated using a regression approach to test the hypothesis that vitamin D was most effective in the weakest and slowest individuals. For hip extensor and adductor strength, but not for the other muscle groups, a significant interaction between treatment group and baseline muscle strength was noted. To explore this effect further, subjects were grouped according to tertile of baseline muscle strength. In those with baseline values in the lowest tertile, hip extensor strength (22.6% (9.5%), P=.0s) and adductor strength (13.5% (6.7%), P=.048) improved significantly in the vitamin D group at 12 months (Table 3). Similarly, TUAG showed a significant interaction between treatment group and baseline value, such that the lowest tertile of the vitamin D group was significantly faster at 12 months (17.5% (7.6%), P=.02) than the control group (Figure 2). These effects remained after adjustment for baseline age and baseline 25(OH)D concentrations.

Figure 2.

Change in Timed Up and Go Test over 12 months according to baseline tertile. Error bars represent standard errors.

The effect of baseline 25(OH)D was examined to investigate whether those with low baseline vitamin D had better muscle strength and mobility response to supplementation than those with higher baseline 25(OH)D levels. Baseline 25(OH)D level was not an effect modifier for the effects of ergocalciferol supplementation on muscle strength and mobility (data not shown).

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