Vitamin D and sudden sensorineural hearing loss: emerging associations, mechanistic insights, and prospects for precision medicine - a review.

Sudden sensorineural hearing loss (SSNHL) is defined as a rapid hearing decline of ≥30 dB across at least three contiguous frequencies within 72 h, with a multifactorial etiology encompassing vascular, viral, autoimmune, and metabolic mechanisms. Beyond its classical role in calcium and phosphorus homeostasis, vitamin D exerts broad biological effects, including immunomodulation, antioxidant defense, endothelial protection, and neuroprotection, which may collectively preserve inner ear function. Multiple observational studies have demonstrated that serum 25-hydroxyvitamin D levels are significantly lower in SSNHL patients than in healthy controls, with deficiency associated with greater hearing impairment, poorer treatment response, and higher recurrence risk. However, it must be emphasized that no standardized serum threshold, population-specific validation, or universally accepted predictive model currently exists; therefore, serum 25(OH)D should be regarded as a candidate-rather than an established-biomarker for SSNHL risk stratification. The causal relationship between vitamin D status and SSNHL remains unestablished, with a Mendelian randomization study finding no significant causal link, and inconsistencies across intervention trials highlighting uncertainties regarding optimal dosage and treatment timing. This review synthesizes current evidence on the mechanisms, clinical associations, and exploratory therapeutic potential of vitamin D in SSNHL, and proposes that future prospective, multicenter studies integrating vitamin D metabolomics and receptor gene polymorphism analyses are essential to identify patient subgroups most likely to benefit, ultimately advancing vitamin D as a candidate biomarker and a potential adjunctive therapeutic consideration in the precision management of SSNHL.