Abstract
BACKGROUND: Sensory impairment is a strong modifiable risk factor for dementia; however, whether vitamin D deficiency (VDD) was associated with increased risk in this high-risk group remains unclear. Individuals with vision or hearing impairment are prone to VDD due to reduced sunlight exposure, making this question clinically relevant. METHODS: From the TriNetX Global Collaborative Network, this retrospective cohort study identified adults aged ≥50 years with documented vision and/or hearing impairment and serum 25-hydroxyvitamin D [25(OH)D] measurement. Patients were classified into VDD group (<20 ng/mL) and control group (≥30 ng/mL). The index date was defined as the date of the first 25(OH)D measurement that met the cohort-specific threshold and satisfied all eligibility criteria. The primary outcome was incident dementia over a 10-year follow-up. Secondary outcomes included dementia subtypes (i.e., vascular dementia and Alzheimer's disease), cognitive impairment, osteoporotic fracture (positive control), healthcare visits (detection bias assessment), and recurrent VDD. RESULTS: After propensity score matching, 158,382 patients were included in each cohort. Compared to the control group, the VDD group was associated with a significantly higher risk of incident dementia [hazard ratio (HR), 1.55; p < 0.001], vascular dementia (HR, 1.70; p < 0.001), Alzheimer's disease (HR, 1.48; p < 0.001), cognitive impairment (HR, 1.40; p < 0.001), and subsequent VDD (HR, 4.73; p < 0.001). The risk of osteoporotic fracture was significantly associated with VDD (HR, 1.34; p < 0.001), whereas healthcare visits were slightly lower in the VDD group (HR, 0.91; p < 0.001), arguing against detection bias. Vitamin D insufficiency was associated with a significant but attenuated association with dementia (HR, 1.39; p < 0.001). CONCLUSION: In this cohort study, VDD was associated with an increased risk of incident dementia in adults with vision and/or hearing impairment, with exploratory findings supportive of a graded pattern. Although residual confounding cannot be excluded, these findings raise the possibility that low vitamin D status may be a potentially modifiable contributor to dementia risk in sensory-impaired populations.