Níveis de vitamina D e desempenho cognitivo de pessoas idosas cognitivamente saudáveis e com doença de Alzheimer residentes na comunidade: um estudo transversal

Abstract

In recent years, there has been an increase in studies suggesting a relationship between vitamin D levels and brain health. Both the vitamin D receptor and the enzyme that converts 25-hydroxyvitamin D into its active form are expressed in all organs of the body, including brain regions responsible for cognition, mainly the hippocampus, thalamus, hypothalamus, basal ganglia, and cerebellum. Some studies have shown that vitamin D deficiency is associated with a higher risk of cognitive decline and the development of dementias, especially Alzheimer's disease (AD). Other evidence indicates that this association is not yet consistent. Objectives: To investigate the association between serum vitamin D levels and cognitive performance in cognitively healthy older adults and in people living with AD dementia. Methods: This is an analytical observational study with a cross-sectional design. Participants were grouped into two groups: cognitively healthy (n = 147) and with AD (n = 53). The assessment protocol consisted of the following instruments: Sociodemographic questionnaire and health information; Addenbrooke's Cognitive Examination Revised (ACE-R); Mini-Mental State Examination (MMSE); Digit Span Test; Trail Making Test (TMT); Consortium for Establishing a Registry of Alzheimer's Disease (CERAD); Memory Complaints Scale (MCS); Clinical Rating Scale for Dementia (CDR); Geriatric Depression Scale (GDS); Katz Scale; and Lawton and Brody Scale. In addition, blood vitamin D levels were assessed in elderly individuals in the cognitively healthy group. Data were analyzed using the R statistical software. Categorical variables were presented as frequencies and percentages, and continuous variables as mean ± standard deviation and median (interquartile range). For comparisons between groups, the chi-square test, Welch's t-test, and Mann-Whitney test were used, depending on the data distribution. Linear regression models were used to assess the association between vitamin D levels and cognitive outcomes (global score and ACE-R), adjusted for age, sex, education, depressive symptoms, and APOEε4 status. Sensitivity analyses included variables related to sun exposure. Missing data were handled using multiple imputation (MICE), and the Benjamin-Hochberg correction was applied for multiple comparisons. The significance level adopted was 5% (p < 0.05). Results: Individuals with dementia were older (79.0 ± 7.7 years), had lower education (7.1 ± 5.2 years), a higher frequency of the APOE ε4 allele (60.4%), and worse performance on all cognitive tests (p < 0.001), with no significant difference in serum vitamin D levels between the groups. In the adjusted models, vitamin D was not associated with global cognitive performance or ACE-R. Conversely, as expected, older age, the presence of the APOEε4 allele, and depressive symptoms were associated with poorer cognition, whereas higher education was associated with better cognitive performance (p < 0.05). The inclusion of variables related to sun exposure did not modify the results. Conclusion: Serum vitamin D levels were not associated with cognitive performance in older adults, regardless of the diagnostic group. On the other hand, factors such as age, education, presence of the APOEε4 allele, and depressive symptoms showed a significant association with cognition. These findings reinforce the multifactorial nature of cognitive aging and suggest that vitamin D may play a limited role when analyzed in isolation.