The effect of vitamin D plus protein supplementation on sarcopenia: A systematic review and meta-analysis of randomized controlled trials

Purpose: The exact effect of vitamin D supplementation, either as monotherapy or in combination with protein, on musculoskeletal health in patients with sarcopenia is currently unknown. This study aimed to determine the effect of vitamin D alone or with protein supplementation on muscle strength, mass, and performance in this population. Methods: A comprehensive search was conducted in Medline, Cochrane Central and Scopus databases, up to March 31st, 2020. Data were expressed as standardized mean difference (SMD) with 95 % confidence intervals (CI). I-2 index was employed for heterogeneity. Results: The initial search identified 1164 studies, eight of which met the eligibility criteria for qualitative and quantitative analysis, yielding a total of 776 patients. Vitamin D (100-1600 IU/day) plus protein (10-44 g/day) supplementation exhibited a beneficial effect on muscle strength, as demonstrated by an improvement in handgrip strength (SMD 0.38 +/- 0.07, 95 % CI 0.18-0.47, p = 0.04; I-2 76.2 %) and a decrease in the sit-to-stand time (SMD 0.25 +/- 0.09, 95 % CI 0.06-0.43, p = 0.007; I-2 0%) compared with placebo. However, the effect on muscle mass, assessed by skeletal muscle index, was marginally non-significant (SMD 0.25 +/- 0.13, 95 % CI-0.006-0.51, p = 0.05; I-2 0%). No effect on appendicular skeletal muscle mass or muscle performance (assessed by walking speed) was observed with vitamin D plus protein. Conclusions: Vitamin D supplementation, combined with protein, improves muscle strength in patients with sarcopenia, but has no effect on muscle mass or performance.