The synergistic interaction of vitamin D deficiency and insomnia on dizziness-related handicap in patients with benign paroxysmal positional vertigo.

BACKGROUND: While insomnia and vitamin D deficiency are known risk factors for BPPV, their interactive effect on the dizziness-related handicap is unknown. Given that both may independently promote pro-inflammatory states, a synergistic interaction is biologically plausible. Therefore, this study aimed to investigate both the independent and interactive effects of insomnia and 25-OH-D levels on the dizziness-related handicap in BPPV patients. We specifically hypothesized that insomnia amplifies the detrimental impact of low vitamin D, aiming to provide an empirical basis for integrated clinical management strategies. METHODS: In this cross-sectional study, 125 patients with BPPV were enrolled. Serum 25-OH-D levels and Dizziness Handicap Inventory (DHI) scores were measured. A multivariable linear regression model, refined by a systematic variable selection procedure, was used to assess the effects of insomnia and 25-OH-D on log-transformed DHI scores after adjusting for potential confounders. RESULTS: After multivariable adjustment in the final parsimonious model, insomnia, lower 25-OH-D levels, and their interaction term all remained highly significant predictors of higher dizziness-related handicap (all p < 0.01). The interaction indicated that the negative association between 25-OH-D and DHI was significantly stronger in patients with insomnia. CONCLUSION: Insomnia and vitamin D deficiency are independently associated with greater dizziness-related handicap in BPPV patients, and they demonstrate a significant synergistic interaction. However, due to the study's design, a definitive causal relationship cannot be established. Assessing and managing both conditions may be crucial for mitigating the handicap imposed by BPPV.