Influence of Vitamin B12 Deficiency on Auditory and Vestibular Functioning: An Objective Test-Based Systematic Review.

OBJECTIVE: To evaluate the effectiveness of objective audiological and vestibular assessments in detecting functional changes associated with vitamin B12 deficiency. DATA SOURCES: A comprehensive literature search was conducted in PubMed, Scopus, Web of Science, and EMBASE databases. REVIEW METHODS: This PROSPERO-registered systematic review (CRD420251049105) followed a structured search strategy based on the PICO framework. Two independent reviewers screened titles, abstracts, and full texts of eligible studies. Data extraction and quality assessment were performed independently using the Mixed Methods Appraisal Tool (MMAT), with disagreements resolved by a third reviewer. Studies investigating objective auditory and vestibular assessments, including Auditory Brainstem Response (ABR), Otoacoustic Emissions (OAE), and Vestibular Evoked Myogenic Potentials (VEMP), in individuals with vitamin B12 deficiency were included. RESULTS: Eleven studies met the inclusion criteria. Evidence suggests that vitamin B12 deficiency affects neural conduction and cochlear function, as demonstrated by prolonged ABR latencies and reduced Transient Evoked OAEs (TEOAE) and Distortion Product OAEs (DPOAE) amplitudes. Vestibular findings were inconsistent, with some studies reporting absent cVEMP responses and others finding no significant association in ENG/VNG assessments. In infant populations, vitamin B12 supplementation resulted in partial or complete recovery of auditory conduction. CONCLUSION: Vitamin B12 deficiency adversely affects neural transmission and cochlear micromechanics. Objective electrophysiological assessments, such as ABR and OAE, are sensitive indicators of subclinical neuropathy. Although vestibular involvement remains inconclusive, integrating electrophysiological and behavioral assessments may facilitate early diagnosis and timely intervention to prevent irreversible auditory dysfunction.