Vitamin D and arthritis

Abstract

Vitamin D is a pleiotropic steroid molecule that exerts its physiological effects through the ubiquitous vitamin D receptor. Vitamin D is formed from its precursor in the skin upon exposure to the sunlight. Its importance in calcium homeostasis has been well known for a century, but recently several non-calcemic effects have been recognized. Vitamin D regulates several genes involved in cellular differentiation, apoptosis and has immunomodulatory effects. Epidemiologic data suggest that vitamin D deficiency may increase the risk of common cancers and autoimmune diseases. In experimental animal models, autoimmune diseases can be ameliorated by treatment with active vitamin D metabolites. Potential use of vitamin D supplementation to modify these diseases would certainly be a novel approach. Preliminary data from cross-sectional studies show that low vitamin D levels may be associated with increased disease activity in rheumatoid arthritis. Other studies show a possible increased risk of osteoarthritis with low vitamin D levels. These findings, while interesting, are not confirmed by all studies. Moreover, the cross-sectional design of these studies does not establish causality. Currently, the optimal and minimal level of vitamin D required for its physiological functions in humans is unknown. We, thus, await more research and randomized controlled interventional trials to answer these critical questions.