TNF and vitamin D deficiency: Additionally, studies on rats have found that serum vitamin D deficiency plays a role in the etiology of deep muscle pain and that its supplementation can decrease the levels of plasma creatine kinase (CK) and some proinflammatory cytokines by reducing the gene expression of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) [21,22].