Current perspectives on vitamin D, immune system, and chronic diseases.

Accumulating data support that vitamin D possesses several biological and molecular actions apart from its role in calcium homeostasis. Immune cells express vitamin D receptor and are capable of metabolizing vitamin D. Within this context, experimental studies show that vitamin D modulates immune and inflammatory responses. Epidemiologic evidence linking poor vitamin D status to autoimmune diseases, type 2 diabetes, and cardiovascular disease suggests that insufficient vitamin D may be involved in the etiology of such disorders. Given the impact of immune and inflammatory abnormalities in the development of chronic diseases, including autoimmune disorders, it is possible that vitamin D might reduce chronic disease risk by modulating the immune system.