Vitamin D status in patients with oral leukoplakia and oral squamous cell carcinoma: a systematic review and meta-analysis.

BACKGROUND: Vitamin D deficiency has been widely evidenced to be associated with promoting cancer progression. Herein, we performed a meta-analysis and systematic review of studies assessing vitamin D status in oral leukoplakia (OLK) and oral squamous cell carcinoma (OSCC). METHODS: This review was registered in PROSPERO (CRD420251113481) and followed PRISMA guidelines. We searched PubMed, Embase, Scopus, and Web of Science, with manual searches of reference lists through August 2025. Meta-analyses of proportion deficiency were performed using random-effects models. RESULTS: A total of seven studies met inclusion criteria, involving a total of 317 healthy controls, 45 OLK patients, and 168 OSCC patients. Vitamin D deficiency rates were 45% (threshold: 30 ng/mL) and 65% (35 ng/mL) in healthy controls, exceeding 90% in OLK/OSCC patients at both thresholds. Compared with healthy controls, a significant difference was observed in the forest plot in OLK patients (odds ratio (OR) = 36.84, 95% CI: 7.35–184.51, I2 = 0%), and in OSCC patients (OR = 32.43, 95% CI: 4.40–238.96, I2 = 35.5% at 30 ng/mL; OR = 4.67, 95% CI: 2.31–9.45, I2 = 0% at 35 ng/mL). Serum vitamin D concentrations were consistently lower in OSCC patients than healthy controls (pooled weighted mean differences: -15.35 ng/mL, 95% CI: -19.33 ng/mL to -11.36 ng/mL, I2 = 66.4% ). CONCLUSION: This systematic literature review and meta-analysis demonstrated that patients with OLK or OSCC exhibit significantly higher rates of vitamin D deficiency and lower serum concentrations compared to healthy controls. Therefore, the assessment of vitamin D status may be considered in clinical practice for individuals with OLK or OSCC.