Relationship between 25-hydoxyvitamin D, muscle strength, and incidence of injury in healthy adults: a systematic review.

The purpose of this systematic review is to answer the following clinical questions in healthy adults: is vitamin D status related to (1) muscle strength? (2) or incidence of injury? A literature search was performed using Pubmed, SPORTDiscus, and Web of Science to capture relevant articles that have examined these outcomes. Inclusion criteria required studies to address at least one of the 2 questions stated above, enroll healthy human subjects with a mean age of 18 to 65 years of age, and include serum 25-hydoxyvitamin D measures. Study characteristics such as vitamin D status, study design, and study population were documented. Measured assessors and outcomes from all studies were extracted to answer at least one of the two questions. When applicable, data were used to compute effect sizes at a 95% confidence interval for comparisons across studies to answer the 2 questions. The results of these studies indicate a weak to moderate effect of higher 25-hydoxyvitamin D levels on greater muscle strength and reduced incidence of injury. Randomized controlled clinical trials examining these questions are scarce when compared with the popularity of vitamin D testing; therefore, future trials are necessary to advance our understanding and to clarify the effect vitamin D has on extraskeletal outcomes in healthy adults.