Introduction. Vitamin D deficiency is widespread worldwide
and has been linked with disturbances in glucose metabolism,
although evidence remains inconsistent. The aim of this study
was to evaluate serum 25(OH)D levels and their crude associations with glycemic control and chronic diabetic complications
in patients with type 2 diabetes mellitus (T2DM).
Methods. This retrospective study included 170 adults with
T2DM treated at the University Clinical Centre of Republic of
Srpska from January 2023 to June 2024. Patients were categorized according to serum 25(OH)D concentration into two
groups: low vitamin D (≤ 30 ng/mL) and normal vitamin D (≥
31 ng/mL). Collected data included age, sex, body mass index
(BMI), diabetes duration, treatment modalities, fasting plasma
glucose (FPG), 2-hour postprandial glucose (PPG), HbA1c, and
documented complications (retinopathy, neuropathy, diabetic
kidney disease, atherosclerotic cardiovascular disease). Normality was assessed using Q–Q plots and the Shapiro–Wilk test;
group comparisons were performed using Student’s t-test or
non-parametric equivalents; correlations were evaluated using
Pearson or Spearman coefficients. Due to the retrospective design and limited number of available covariates, no multivariable regression analyses were performed.
Results. Patients with lower 25(OH)D levels had significantly longer diabetes duration, higher BMI, and higher values of
HbA1c, FPG and PPG. Weak negative correlations were observed
between 25(OH)D and glycemic parameters (r values between
–0.13 and –0.25). The prevalence of chronic diabetic complications was significantly higher in the low 25(OH)D group. All presented results were unadjusted.
Conclusion. In this retrospective analysis, lower 25(OH)D levels
were accompanied by poorer glycemic parameters and higher
prevalence of chronic diabetic complications in patients with type
2 diabetes mellitus. However, the groups differed significantly in
diabetes duration and BMI, and all presented results were unadjusted. Therefore, the observed differences cannot be attributed
exclusively or predominantly to vitamin D levels. The findings indicate an association, but do not demonstrate causality
