Vitamin D Deficiency in Institutionalized Older Adults: Associations with Supplementation Practices but Not with Cognitive Decline or Dementia

Background/Objectives: Population aging has been accompanied by increased institutionalization of older adults and a high prevalence of vitamin D deficiency in this group. Although the literature suggests a possible relationship between vitamin D and cognition, findings remain inconsistent, particularly in institutional settings. This cross-sectional study aimed to investigate factors associated with vitamin D deficiency in institutionalized older adults, emphasizing the role of vitamin D supplementation and length of institutionalization, as well as to evaluate the association between serum vitamin D levels, cognitive decline, and dementia. Methods: A total of 104 older adults living in different long-term care institutions (LTCFs) in the city of Pelotas, RS, Brazil, were evaluated. Sociodemographic, clinical, and nutritional data were collected via interviews and medical record review. Serum 25-hydroxyvitamin D levels were categorized according to the Institute of Medicine cutoffs (<20 ng/mL and ≥20 ng/mL). Cognitive decline was assessed using the Mini-Mental State Examination, and dementia was evaluated with the Clinical Dementia Rating scale. Analyses included bivariate tests and binary logistic regression. Results: A high prevalence of vitamin D deficiency (52.9%), cognitive decline (83.6%), and questionable or mild dementia (79.4%) was observed. In multivariate analysis, vitamin D supplementation remained independently associated with vitamin D deficiency, whereas no significant association was observed between vitamin D levels and cognitive decline or dementia. Conclusions: Vitamin D deficiency in institutionalized older adults is predominantly associated with contextual and care-related factors rather than cognitive impairment, highlighting the importance of systematic nutritional monitoring and vitamin D supplementation strategies in institutional settings.