25(OH)D3 and F-25(OH)D as indicators of chronic kidney disease progression in patients with rheumatoid arthritis.

Vitamin D (VitD) deficiency has been associated with the development of rheumatoid arthritis (RA) and chronic kidney disease (CKD), but its exact role in patients with RA and CKD remains unclear. This cross-sectional study explored the relationship of 25(OH)D2, 25(OH)D3, and Free 25(OH)D [F-25(OH)D] with CKD progression in patients with RA. Patients with RA (n = 1514) were enrolled and divided into the mild, moderate, and severe CKD groups. Total 25(OH)D, 25(OH)D3, and F-25(OH)D in the moderate and severe CKD groups were lower than in the mild CKD group (all P < 0.05), while there were no differences in 25(OH)D2 levels (P = 0.095). As the severity of CKD progressed, total 25(OH)D, 25(OH)D3, and F-25(OH)D decreased (all Padj.<0.05). When progressing from moderate to severe CKD, only 25(OH)D3 decreased significantly (Padj.=0.014). Partial correlation and multiple logistic regression analyses revealed a significant association between 25(OH)D3 and the progression of CKD deterioration, as did F-25(OH)D (all P < 0.05). Further seasonal stratified analysis showed that this correlation existed only in spring, summer, and autumn for 25(OH)D3 and only in spring and summer for F-25(OH)D (P < 0.05). In conclusion, the serum 25(OH)D3 and F-25(OH)D levels may be indicators of CKD progression in patients with RA to plan for timely intervention and management.