Relationship between vitamin D status, glycemic control and chronic diabetic complications in type 2 diabetes mellitus: a retrospective study

<p data-start="0" data-end="341"><strong data-start="0" data-end="17">Introduction.</strong> Vitamin D deficiency is common worldwide and has been associated with disturbances in glucose metabolism, although evidence remains inconsistent. This study evaluated serum 25(OH)D levels and their crude associations with glycemic control and chronic diabetic complications in patients with type 2 diabetes mellitus (T2DM).</p> <p data-start="343" data-end="1179"><strong data-start="343" data-end="355">Methods.</strong> This retrospective study included 170 adults with T2DM treated between January 2023 and June 2024. Participants were categorized according to serum 25(OH)D concentration into a low vitamin D group (≤30 ng/mL) and a normal vitamin D group (≥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, and 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, and correlations were evaluated using Pearson or Spearman coefficients. No multivariable regression analyses were conducted.</p> <p data-start="1181" data-end="1558"><strong data-start="1181" data-end="1193">Results.</strong> Patients with lower 25(OH)D levels had significantly longer diabetes duration, higher BMI, and higher HbA1c, FPG, and PPG values. Weak negative correlations were observed between 25(OH)D and glycemic parameters (r = –0.13 to –0.25). The prevalence of chronic diabetic complications was significantly higher in the low vitamin D group. All findings were unadjusted.</p> <p data-start="1560" data-end="1814" data-is-last-node="" data-is-only-node=""><strong data-start="1560" data-end="1575">Conclusion.</strong> Lower 25(OH)D levels were associated with poorer glycemic parameters and a higher prevalence of chronic diabetic complications in T2DM. However, given significant group differences and the lack of adjustment, causality cannot be inferred.</p>