On April 7, 2015, MPR published an article entitled “The Vitamin D Debate: Conundrums and Complexities.” Readers expressed a strong interest in a follow-up article. The current article, which summarizes representative studies on the role of Vitamin D in musculoskeletal conditions, HIV, multiple sclerosis, heart failure, childhood asthma, urticaria, and Alzheimer’s disease, is a response to our readers’ requests.

The essential role that Vitamin D (usually defined as 25-hydroxy vitamin D (25(OH)D) plays in skeletal health is well established.1 An emerging body of research suggests that Vitamin D may play an important role in other conditions as well, although controversy continues regarding Vitamin D supplementation as a way of addressing or preventing these conditions.1,2

Vitamin D Improves Muscle Health

Several musculoskeletal conditions have been linked to Vitamin D deficiency, including diffuse and nonspecific musculoskeletal pain, muscle weakness in the elderly, sarcopenia, myopathy, falls related to muscle wasting, and falls related to cerebellar and cognitive dysfunction.3

Vitamin D affects extra-skeletal tissues via the vitamin D receptor (VDR), a transcription factor activated by 1,25-dihydroxyvitamin D (the biologically active metabolite of Vitamin D) to regulate gene transcription. VDR is involved with mineral homeostasis and skeletal health. It has been found in almost all cell types and is present on skeletal muscle.3 Validating the role of VDR may contribute to understanding the impact of Vitamin D deficiency in these conditions. Existing data already suggest that Vitamin D supplementation may contribute to the health and maintenance of muscle function and that the musculoskeletal benefits of Vitamin D supplementation outweigh any potential risks.3