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Chapter 6

Abstract

Vitamin D in Rheumatic Diseases:

The pleiotropic effects of vitamin D on the various metabolic, anticancer, and immunomodulatory functions of the body based on the presence of vitamin D receptors (VDR) on various cell types has been recognized worldwide now. Of few understood mechanisms of immunomodulatory actions of vitamin D are the

suppressive action on the maturation of antigen-presenting cells and decrease in the levels of pro-inflammatory cytokines. Vitamin D deficiency has been implicated in the immune diseases like rheumatic diseases, asthma, psoriasis, and multiple sclerosis. Vitamin D deficiency has been associated with increased frequency and severity of disease flares in rheumatic diseases like lupus and rheumatoid arthritis. Other studies have shown higher prevalence of persistence and evolution in to more definite rheumatic disorder in undifferentiated arthritis and undifferentiated connective tissue disorder patients with vitamin D deficiency. Multiple factors like avoidance of sunlight, the use of corticosteroids and hydroxychloroquine, skin pigmentation, etc. should be considered when evaluating vitamin D levels in these patients, needless to say the consideration of higher-dose supplement for these patients. It is thus prudent that all patients with established or undifferentiated rheumatic diseases are evaluated for vitamin D status and an adequate supplemen-

Vitamin D has two bioequivalent forms, D2 (ergocalciferol) and D3 (cholecalciferol). It is synthesized mainly from 7-dehydrocholesterol in keratinocytes of the skin stimulated by UVB of sunlight and metabolized in the liver to 25(OH)D and subsequently converted to its active form 1,25(OH)2D in the kidney [1, 2]. It maintains calcium and phosphorus homeostasis, optimizes bone health and muscle function and immunomodulation, has antiproliferative effect on keratinocytes, and suppresses cytokine production [3, 4]. Serum 25(OH)D3 level of at least 50 nmol/l is considered to be optimal for bone health and extra skeletal effects [5]. The term hypovitaminosis D includes vitamin D insufficiency and deficiency. Vitamin D insufficiency is defined as a serum 25(OH)D concentration of 21– 29 ng/ml (50–75 nmol/L), whereas deficiency means serum 25(OH)D level of

tation is recommended to prevent the associated consequences.

rheumatic diseases, inflammation

<20 ng/ml (<50 nmol/L) [6].

83

1. Introduction

Keywords: vitamin D, vitamin D deficiency, immunomodulation,

Interpretation and Significance

Binit Vaidya and Shweta Nakarmi
