A recent meta-analysis of controlled trials published in Journal of Science and Medicine in Sport suggests that vitamin D supplementation increases both lower and upper limb muscle strength.
As many of our readers know, vitamin D’s more classic roles in human health involve the muscles and the bones. Studies consistently show that vitamin D increases muscle strength by increasing the size of muscle fibers and increasing the rate of protein synthesis.
Much of this research has been in the form of randomized controlled trials, meaning researchers can confidently make statements of causality based on results from these trials. With that said, some trials indicate a positive effect for vitamin D on muscle strength, while others suggest vitamin D has no role.