Associations between serum 25-hydroxyvitamin D and prognosis of chronic kidney disease: a prospective cohort study

25-hydroxyvitamin D [25(OH)D] deficiency is prevalent in patients with chronic kidney disease (CKD), the associations between serum 25(OH)D levels and mortality in patients with CKD remain unclear, and this study aimed to explore these associations further. 4989 participants with CKD were enrolled in the study, and the Cox regression model was used to assess the effects of serum 25(OH)D concentrations on mortality risk. A restricted cubic spline model was used to explore the dose–response relationships, and threshold effect analysis was performed based on inflection points identified by a two-piecewise linear regression model. In addition, subgroup and sensitivity analyses were employed. 1255 participants died during a mean follow-up period of 70 months. Compared with the 25(OH)D-deficient group, the fully adjusted hazard ratios and 95% confidence intervals for the 25(OH)D-adequate group were 0.631 (0.545, 0.730) for all-cause mortality, 0.569 (0.435, 0.743) for cardiovascular mortality, 0.637 (0.461, 0.878) for hypertension mortality, and cancer mortality was 0.596 (0.426, 0.834). The inflection points of serum 25(OH)D concentration affecting all-cause and cardiovascular mortality were 89 nmol/L, and 107 nmol/L, respectively. Subgroup analyses and interaction tests suggested that the effects varied across populations. The results of sensitivity analyses indicated a reliable correlation. We found an association between serum 25(OH)D concentrations and the prognosis of patients with CKD as a reliable predictor of early intervention and intensive care.