The Relationship Between Serum Vitamin D Levels and the First-Attempt Success of the Epley Maneuver in Posterior Canal Benign Paroxysmal Positional Vertigo (PC-BPPV).

Background/Objectives: Vitamin D deficiency has been associated with the occurrence and recurrence of benign paroxysmal positional vertigo (BPPV), but its influence on the immediate success of canalith repositioning maneuvers remains uncertain. This study investigated the relationship between serum vitamin D levels and the first-attempt success of the Epley maneuver in patients with posterior canal BPPV (PC-BPPV). Methods: This prospective observational study included 140 consecutive adults with objectively confirmed unilateral PC-BPPV. Serum 25-hydroxyvitamin D levels were measured at presentation before treatment. All patients underwent a standardized Epley maneuver. First-attempt success was defined as complete resolution of positional vertigo and disappearance of positional nystagmus on the Dix-Hallpike test at the one-week follow-up visit. Serum vitamin D levels were analyzed both as a continuous variable and according to laboratory reference ranges: deficiency (<50 nmol/L), insufficiency (50-75 nmol/L), and sufficiency (75-250 nmol/L). Results: The Epley maneuver was successful after the first attempt in 74 of 140 patients (52.9%). In the primary, pre-specified analysis, first-attempt success was more frequent among patients with serum vitamin D ≥50 nmol/L than <50 nmol/L (60.9% vs. 46.1%; OR 1.83, 95% CI 0.93-3.59, p = 0.079), a difference that did not reach statistical significance. In unadjusted exploratory analyses, patients with first-attempt success had significantly higher median serum vitamin D levels than those with treatment failure (52.2 [IQR, 30.0-68.4] vs. 36.8 [IQR, 21.3-66.1] nmol/L, p = 0.029), and success rates numerically increased across the three-tier classification (46.1%, 62.2%, 59.3%), without a clear dose-response pattern, neither the overall comparison (p = 0.208) nor pairwise subgroup comparisons reaching statistical significance. In a multivariable model adjusting for age, sex, and month of enrolment, vitamin D remained independently, though modestly, associated with first-attempt success (adjusted OR 1.14 per 10 nmol/L, 95% CI 1.00-1.29). Conclusions: The pre-specified primary comparison of first-attempt Epley maneuver success between vitamin D-deficient and non-deficient patients did not reach statistical significance, although the point estimate favored higher success in the non-deficient group (OR 1.83, 95% CI 0.93-3.59). An exploratory, initially unadjusted analysis suggested a positive, modest association between serum vitamin D as a continuous variable and first-attempt success; this association persisted after multivariable adjustment (adjusted OR 1.14, 95% CI 1.00-1.29) but did not follow a clear dose-response pattern across categorical vitamin D thresholds. These findings should be regarded as hypothesis-generating rather than establishing a definitive prognostic role for vitamin D, and larger, adequately powered multicenter studies are needed to confirm them.