Association between vitamin D deficiency and chronic kidney disease progression: A GRADE-based dose-response systematic review and meta-analysis.

BACKGROUND: This systematic review and dose-response meta-analysis aimed to evaluate the association between serum vitamin D status and chronic kidney disease (CKD) progression. METHODS: We searched PubMed, Scopus, Web of Science, and Embase for relevant observational and cohort studies published between 1990 and 2024. Eligible studies reported baseline vitamin D levels and CKD progression outcomes. We performed a random-effects meta-analysis to calculate the pooled odds ratio (OR) for CKD progression. A dose-response meta-analysis examined the relationship between serum 25-hydroxyvitamin D (25(OH)D) levels and risk, while subgroup analyses explored follow-up duration, study quality, and comorbid conditions. We assessed evidence certainty using the Grading of Recommendations Assessment, Development and Evaluation approach. RESULTS: Eleven studies met the inclusion criteria. The pooled analysis suggested that vitamin D deficiency was associated with 33% higher odds of CKD progression (OR = 1.33, 95% confidence interval [CI]: 1.06-1.67; P = .019); however, between-study heterogeneity was considerable (I-squared heterogeneity statistic [I2] = 98.2%). The pooled estimate should therefore be interpreted cautiously as an average association across heterogeneous studies. A dose-response analysis of 10 studies suggested higher odds of CKD progression per 10 ng/mL lower 25(OH)D concentration (OR = 1.18, 95% CI: 1.09-1.25), although its interpretation was limited by reconstructed category-level exposure values. Subgroup analyses showed stronger associations in studies with long-term follow-up (≥5 years; OR = 2.07, 95% CI: 1.29-3.14; P = .001) and high-quality studies (OR = 1.35, 95% CI: 1.06-1.69; P = .03). The Grading of Recommendations Assessment, Development and Evaluation assessment rated the certainty of evidence as very low for the overall association and low for the dose-response analysis, primarily because of the observational study designs and substantial between-study heterogeneity. CONCLUSION: Lower serum 25(OH)D levels were associated with higher odds of CKD progression. However, the observational nature of the evidence does not establish that routine screening or vitamin D supplementation can prevent renal function decline. Prospective studies and randomized trials are needed to clarify the clinical utility of vitamin D assessment and supplementation for renal outcomes.