Serum Vitamin D Levels in Patients with Vernal Keratoconjunctivitis: A Systematic Review and Meta-Analysis

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ABSTRACT Purpose To conduct a systematic review and meta-analysis to provide an outline of available data on the association between serum vitamin D levels and vernal keratoconjunctivitis (VKC) and to determine the possible relationship in children. Methods Systematic research on all articles published until July 2023 was conducted in PubMed, SCOPUS, Web of Science, and Embase. All observational-analytical studies that measured vitamin D levels in patients with VKC were included. Extracted data were included in two separate meta-analyses: 1) a meta-analysis on the standardized mean difference (SMD) of vitamin D levels between VKC patients and the control group and 2) a meta-analysis on the prevalence of vitamin D deficiency in VKC patients. Results Seven relevant studies that included 316 patients, with the mean age of 10.8 3 ± 1.14 years, with VKC were included in this meta-analysis. The mean serum vitamin D level was significantly lower in the patients with VKC as compared with the control group (SMD: −0.92; 95% CI −1.15, −0.69, p < 0.001). The overall prevalence of vitamin D deficiency among VKC patients was 63.7% (95% CI 42.5%-80.7%, p < 0.001). VKC patients spent significantly less time outdoors during daylight compared to healthy individuals (SMD = −0.90, 95%CI −1.28, −0.52, p < 0.001). Conclusion VKC patients have lower serum vitamin D than healthy controls. This finding underscores the potential role of vitamin D in the immunopathogenesis of VKC.