Serum 25(OH)D3 level is associated with cognitive impairment in middle-aged and elderly patients with type 2 diabetes mellitus

Objectives: This study aimed to investigate the association between serum 25-hydroxyvitamin D3 (25(OH)D3) levels and cognitive impairment (CI) in middle-aged and elderly individuals with type 2 diabetes mellitus (T2DM). Additionally, we sought to evaluate the potential of serum 25(OH)D3 as a marker associated with CI and to identify relevant influencing factors. Methods: This cross-sectional study included 221 middle-aged and elderly patients with T2DM, aged 50-80 years. Participants were divided into a group without cognitive impairment (n = 131, 59.28%) and a group with cognitive impairment (n = 90, 40.72%) based on cognitive function status. Demographic characteristics, clinical indicators (e.g., age, disease duration, body composition, comorbidities), and laboratory test results (e.g., 25(OH)D3, fasting C-peptide, fasting insulin, blood lipids) were collected. Logistic regression analysis was used to examine the association between 25(OH)D3 and cognitive impairment. Analyses included univariate logistic regression, multivariate regression adjusted for three sets of confounders, subgroup analyses, interaction tests, and ROC curve analyses. Results: The two groups showed statistically significant differences in age, disease duration, fasting C-peptide, fasting insulin, cholesterol, serum 25(OH)D3 levels, and 25(OH)D3 quartile distribution (P < 0.05). Differences in other indicators were not statistically significant (P > 0.05). Logistic regression analysis revealed that higher serum 25(OH)D3 levels were significantly associated with a lower prevalence of cognitive impairment. This association remained robust after adjusting for multiple confounders (including gender, hypertension, cerebral infarction, and coronary heart disease) in Model 3 (OR = 0.92, 95% CI: 0.88-0.97, P < 0.001). In the 25(OH)D3 quartile subgroup analysis, compared with the Q1 group, the Q3 (OR = 0.35, P = 0.034) and Q4 (OR = 0.25, P = 0.004) groups showed significantly lower odds of cognitive impairment, with a significant trend (P = 0.003). Receiver operating characteristic (ROC) curve analysis revealed an area under the curve (AUC) of 0.65 (95% CI: 0.58-0.72) for 25(OH)D3 in identifying cognitive impairment. Interaction tests indicated that factors such as gender, hypertension, cerebral infarction, and fatty liver did not significantly modify the association between 25(OH)D3 and cognitive impairment (P for interaction > 0.05). Conclusions: This study found that 25(OH)D3 levels were negatively correlated with the prevalence of cognitive impairment in middle-aged and elderly individuals with T2DM. Higher 25(OH)D3 levels are associated with lower odds of cognitive impairment, and 25(OH)D3 may have potential as a marker for cognitive impairment in this population. These findings highlight 25(OH)D3 as a potential factor of interest for further research into the prevention and intervention of cognitive impairment in middle-aged and elderly patients with T2DM.