Vitamin D and Immune System: Implications in Bone Health

Recent studies have identified the involvement of the immune system in several bone complications like osteoporosis, rheumatoid arthritis (RA), periodontitis, osteoarthritis, etc. Immune cells have an indispensable role in the regulation of bone metabolism and explicitly influence the differentiation of bone cells by producing various cytokines. Fortunately, recent research has examined different immune-based therapeutics for the prevention of bone diseases in addition to revealing more information about the interaction of the bone and the immune system. Vitamin D maintains bone health by effectively absorbing calcium and thereby promoting bone mineralization. In addition, vitamin D has great immunomodulatory potential and can influence the effect of immune cells and cytokines on the pathogenesis of bone deformities. Therefore, it is plausible to suggest that the detrimental effect of vitamin D deficiency on bone is also linked to the immune system apart from its classic effect on bone mineralization. However, very few studies have enlightened on this aspect of vitamin D-mediated regulation of bone homeostasis which needs to be further unraveled. In the present chapter, we have compiled recent studies highlighting the effect of vitamin D on bone health via its effect on the host immune system. Further, we have also highlighted the role of the immune system in the maintenance of skeletal health and then have discussed the effect of vitamin D on various immune cells. In addition, we have reviewed vitamin D-facilitated immune-based approaches for the effective management of various bone pathologies such as osteoporosis, osteoarthritis and rheumatoid arthritis. This information will supposedly help in revealing further mechanistic insights into the immunological regulation of bone health by vitamin D.