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

Abstract and Introduction

Abstract

Objectives: To evaluate the effects of vitamin D treatment on muscle strength and mobility in older women with vitamin D insufficiency.
Design: One-year population-based, double-blind, randomized, controlled trial.
Setting: Perth, Australia (latitude 32°S).
Participants: Three hundred two community-dwelling ambulant elderly women aged 70 to 90 with a serum 25-hydroxyvitamin D (25(OH)D) concentration less than 24 ng/mL.
Intervention: Vitamin D2 1,000 IU/d or identical placebo; calcium citrate (1 g calcium/d) in both groups.
Measurements: Lower limb muscle strength and mobility as assessed using the Timed Up and Go Test (TUAG).
Results: At baseline, mean±standard deviation serum 25(OH)D was 17.7±4.2 ng/mL; this increased to 24.0±5.6 ng/mL in the vitamin D group after 1 year but remained the same in the placebo group. For hip extensor and adductor strength and TUAG, but not for other muscle groups, a significant interaction between treatment group and baseline values was noted. In those with baseline values in the lowest tertile, vitamin D improved muscle strength and TUAG more than calcium alone (mean (standard error): hip extensors 22.6% (9.5%); hip adductors 13.5% (6.7%), TUAG 17.5% (7.6%), P<.05). Baseline 25(OH)D levels did not influence patient response to supplementation.
Conclusion: Vitamin D therapy was observed to increase muscle function in those who were the weakest and slowest at baseline. Vitamin D should be given to people with insufficiency or deficiency to improve muscle strength and mobility.

Introduction

Older people are at risk of inadequate vitamin D production in the skin because of less sun exposure and poorer ability of the skin to synthesize vitamin D.[1] Low vitamin D status has been implicated as a cause of falling in elderly institutionalized women[2,3] and in community-dwelling women.[4,5] Despite this, the mechanism of action of vitamin D on falls propensity remains unclear and is an important question that arises in conjunction with the question of clinical efficacy. It has been suggested that the effects of vitamin D on de novo protein synthesis mediates its effects on muscle[6,7] through receptors for 1,25(OH)2D in muscle tissue. Specifically, it has been suggested that it is the active vitamin D metabolite (1,25(OH)2D) that binds to a specific vitamin D nuclear receptor (VDR) in the muscle tissue.[8–10]

Several cross-sectional studies have shown that low vitamin D status is related to lower muscle strength and lower physical performance in older people,[11–14] but prospective randomized controlled trials on potential mechanisms have not provided a clear answer. Whereas some vitamin D supplementation studies showed an effect of vitamin D on improving lower extremity muscle strength and function in older people,[2,15,16] others have failed to show any effect.[17–19]

Moreover, there are few studies on the effects of vitamin D supplementation on muscle strength and mobility in older people with low vitamin D status, although a recent study has suggested benefit on mediolateral sway in participants who had large sway at baseline.[20] The aim of this study was to compare the effects of vitamin D2 treatment 1,000 IU/d with placebo for 1 year on muscle strength and mobility in older community-dwelling women with vitamin D insufficiency. The beneficial effects of the intervention on falls risk have been published previously.[5]

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