Are elderly adults with vitamin D deficiency at increased risk of developing dementia? EVIDENCE-BASED ANSWERProbably. Vitamin D (25[OH]-D) deficiency and insufficiency in older adults are associated with a greater risk for developing dementia compared with individuals with sufficient levels of 25(OH)-D, but not Alzheimer's dementia (SOR: B, meta-analysis of cohorts). Additionally, older patients with vitamin D deficiency experience more cognitive decline over time than those with normal levels (SOR: B, systematic review of cohorts and cross-sectional studies, and a single cohort).