Vitamin D3 metabolism in patients with rheumatic diseases: Low serum levels of 25-hydroxyvitamin D3 in patients with systemic lupus erythematosus

Summary 1,25-dihydroxyvitamin D₃ (1,25(OH)₂ D₃) has been shown to modulate lymphocyte activation in vitro. Through binding to specific receptors 1,25(OH)₂ D₃ inhibits proliferation, immunoglobulin production and the release of cytokines. Moreover, 1,25-(OH)₂ D₃ is efficiently produced by activated monocytes. These findings suggest that 1,25-(OH)₂ D₃ may play a role as a regulator of immunological activation. Consequently, we found it of interest to study the serum levels of the two major metabolites of vitamin D₃ in patients with systemic lupus erythematosus (SLE) (n=21), rheumatoid arthritis (RA) (n=29) and osteoarthritis (n=12). In patients with SLE the levels of 25-OH D₃ were below those of the healthy controls (p=0.0008) and OA (p=0.0168). The levels 1,25-(OH)₂ D₃ corresponded to normal levels. There were no significant correlations between 25-OH D₃ levels and clinical or paraclinical disease manifestations. Further, the phenotypic distribution of Gc-globulin, which binds vitamin D₃ metabolites in circulation, was normal. The serum concentrations of 1,25-(OH)₂ D₃ and 25-OH D₃ in patients with RA and OA corresponded to those of the controls. Although the cause of the reduced 25-OH D₃ levels in SLE patients is unclear, possible beneficial effects of administration of vitamin D to these patients should be considered.