A retrospective study on the associations of serum 25-hydroxyvitamin D with N-terminal pro-B-type natriuretic peptide and left ventricular ejection fraction in patients with type 2 diabetes mellitus

Background Accumulating evidence points to a role of vitamin D deficiency in cardiovascular diseases. However, its implications for cardiac dysfunction, particularly in patients with type 2 diabetes mellitus (T2DM), have not been well defined. In the present study, the relationships between serum 25-hydroxyvitamin D (25(OH)D) and markers for cardiac dysfunction were investigated. Methods This retrospective study enrolled 601 participants (210 males, 391 females) with T2DM, aged ≥18 years. Patients with a history of vitamin D supplementation, hyper-/hypoparathyroidism, or incomplete data were excluded. Correlation analyses were conducted to explore the associations of N-terminal pro-B-type natriuretic peptide (NT-proBNP) and left ventricular ejection fraction (LVEF) with serum 25(OH)D and related clinical indexes. Multivariate logistic regression analysis was performed to explore the association between vitamin D deficiency and elevated NT-proBNP. Causal mediation analyses were performed to examine the potential mediating role of urinary microalbumin-to-creatinine ratio (UACR) in the association between vitamin D deficiency and NT-proBNP. A directed acyclic graph (DAG) was constructed to identify confounders for multivariable adjustment and distinguish mediators. Results Of all subjects, 143 (24%) presented vitamin D deficiency and 221 (36.8%) presented vitamin D insufficiency. Elevated NT-proBNP was detected in 266 (44.3%) patients. In patients with vitamin D deficiency, NT-proBNP level was significantly increased compared with those with vitamin D sufficiency or those with vitamin D insufficiency, but LVEF showed no differences among groups. Multivariate logistic regression analysis showed that the odds ratio (OR) for elevated NT-proBNP in patients with vitamin D deficiency was 2.11 (95% CI 1.38-3.2, P < 0.001) versus patients with vitamin D sufficiency. After adjusting for age, sex, BMI, diabetes duration, hypertension, coronary heart disease, HbA1c, and eGFR, the association between vitamin D deficiency and elevated NT-proBNP remained significant (OR 1.833, 95% CI 1.115-3.013, P = 0.017). Mediation analysis revealed that approximately 43.23% of the total effect was statistically compatible with an indirect pathway through UACR. Conclusions Vitamin D deficiency was associated with elevated NT-proBNP, a marker of myocardial wall stress that may signal early cardiac involvement, whereas no association with LVEF was observed. This association was partially accounted for by UACR in exploratory mediation analyses.