ビタミンDと筋力改善のメタ分析

ビタミンDと筋力改善に関するメタ分析の論文を紹介します。

Stockton KA, Mengersen K, Paratz JD, et al: Effect of vitamin D supplementation on muscle strength: a systematic review and meta-analysis. Osteoporos Int 22:859-871, 2011

17のRCT論文のメタ分析の結果として、ビタミンD：25(OH)Dの血中濃度が25nmol/L以上の場合、握力（7論文）も下肢近位筋の筋力（12論文）もビタミンDを投与しても改善しません。ただし、ビタミンD：25(OH)Dの血中濃度が25nmol/L以下の2つの論文のメタ分析では、股関節の筋力増強に効果があるとのことです。

これよりビタミンDが欠乏している患者では、近位筋の筋力改善に有効という結論にしています。ただし、17論文中わずか2論文のメタ分析ですので、エビデンスレベルとしてはメタ分析であっても高いとはいえません。

ビタミンDが欠乏していて実際に筋力低下や筋肉痛を認める患者ではビタミンDを投与すべきだと考えますが、D：25(OH)Dの血中濃度が25nmol/L以下であれば筋力改善目的にルーチンにビタミンDを投与する、という気にはとてもなりません。

Abstract
This systematic review demonstrates that vitamin D supplementation does not have a significant effect on muscle strength in vitamin D replete adults. However, a limited number of studies demonstrate an increase in proximal muscle strength in adults with vitamin D deficiency.

INTRODUCTION: The purpose of this study is to systematically review the evidence on the effect of vitamin D supplementation on muscle strength in adults.

METHODS: A comprehensive systematic database search was performed. Inclusion criteria included randomised controlled trials (RCTs) involving adult human participants. All forms and doses of vitamin D supplementation with or without calcium supplementation were included compared with placebo or standard care. Outcome measures included evaluation of strength. Outcomes were compared by calculating standardised mean difference (SMD) and 95% confidence intervals.

RESULTS: Of 52 identified studies, 17 RCTs involving 5,072 participants met the inclusion criteria. Meta-analysis showed no significant effect of vitamin D supplementation on grip strength (SMD -0.02, 95%CI -0.15,0.11) or proximal lower limb strength (SMD 0.1, 95%CI -0.01,0.22) in adults with 25(OH)D levels > 25 nmol/L. Pooled data from two studies in vitamin D deficient participants (25(OH)D <25 nmol/L) demonstrated a large effect of vitamin D supplementation on hip muscle strength (SMD 3.52, 95%CI 2.18, 4.85).

CONCLUSION: Based on studies included in this systematic review, vitamin D supplementation does not have a significant effect on muscle strength in adults with baseline 25(OH)D >25 nmol/L. However, a limited number of studies demonstrate an increase in proximal muscle strength in adults with vitamin D deficiency.