The association between serum vitamin D level and risk and prognosis of melanoma: a systematic review and meta‐analysis

Background Vitamin D has antineoplastic effects, but the synthesis of vitamin D requires ultraviolet radiation, a known risk factor for melanoma. Objective To investigate the correlations between serum vitamin D levels and risk and prognosis of melanoma. Methods A systematic review and meta‐analysis were conducted. Online databases were searched on 31 Oct 2018. Results Twenty‐five studies with a total of 11166 patients with melanoma were included. There was no significant difference in serum vitamin D levels between patients with melanoma and controls [standardized mean difference (SMD), −0.185; 95% confidence interval (CI), −0.533 to 0.162]. However, the prevalence of vitamin D deficiency was significantly higher in patients with melanoma than that in controls (odds ratio, 2.115; 95% CI, 1.151–3.885). In terms of prognosis, serum vitamin D levels were significantly higher in melanoma patients with lower Breslow thickness (≦1 vs. >1 mm: SMD, 0.243; 95% CI, 0.160–0.327). Moreover, melanoma patients with lower vitamin D levels had a significantly higher mortality rate (hazard ratio, 1.558; 95% CI, 1.258–1.931). Conclusions Vitamin D deficiency is associated with higher Breslow thickness and mortality in melanoma patients.