Abnormal vitamin D3 metabolism in patients with primary Sjögren's syndrome.

Recent studies have suggested that vitamin D3 may have an immunoregulatory role in vitro. The vitamin D3 metabolism in 35 patients with primary Sjögren's syndrome was investigated by measuring blood concentrations of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) and 25-hydroxyvitamin D3 (25-OHD3), as well as phenotypes and blood concentrations of Gc globulin, the main vitamin D3 binding protein in the blood. 25-OHD3 concentrations were diminished, but those of 1 alpha,25-(OH)2D3 were normal. There was no significant difference between the distribution of Gc phenotypes in the patients with primary Sjögren's syndrome and normal controls. Likewise, blood concentrations of Gc globulin corresponded to normal values. Among patients with increased concentrations of IgM rheumatoid factor there was a significant negative correlation between the serum titres of IgM rheumatoid factor and 25-OHD3 concentrations.