Solar Ultraviolet Radiation Exposure, Vitamin D Status, and Risk of Renal Cell Carcinoma: A Systematic Review and Meta-Analysis of Observational Studies

Abstract

Background: The incidence of renal cell carcinoma (RCC) continues to rise. Solar ultraviolet (UV) radiation is the main source of vitamin D, which is activated in the kidney, but individual-level evidence linking sunlight with RCC has not been pooled.

Objective: To quantify the associations of solar UV exposure and of vitamin D status with the incidence of RCC.

Methods: PubMed/MEDLINE, Europe PMC and OpenAlex were searched. Cohort and case-control studies reporting adjusted estimates for occupational, ambient or personal solar UV exposure, or for circulating or predicted 25-hydroxyvitamin D, were eligible. Adjusted relative risks (RR) for the highest versus lowest exposure were pooled separately for each domain with random-effects models (Hartung–Knapp intervals). Risk of bias was rated with the Newcastle–Ottawa Scale and certainty with GRADE.

Results: Eleven studies with 1,045,226 participants were included. In five UV studies (64,648 cases), the highest exposure carried a lower RCC risk: RR 0.84 (95% CI 0.75–0.95), I² 18.2%, prediction interval 0.72–0.99. Occupational studies alone gave 0.84 (0.67–1.06). Vitamin D results came from six studies. Four categorical studies gave 0.55 (0.31–0.98) and two per-doubling studies 0.79 (0.45–1.41); combined, 0.67 (0.48–0.92), yet the prediction interval (0.38–1.18) crossed unity and the largest consortium found no association. Certainty: low for UV, very low for vitamin D.

Conclusion: Individuals with more solar UV exposure had a modestly lower RCC risk, and vitamin D status pointed the same way, though inconsistently. With low certainty, and with UV a cause of skin cancer, the results call for research and do not change sun-protection advice.