Association between serum 25-hydroxyvitamin D levels and glycemic control among individuals with diabetes mellitus from PERSIAN Guilan cohort study

Background Vitamin D deficiency has been proposed as a potential contributor to poor glycemic control in diabetes mellitus. This study aimed to evaluate the association between serum 25-hydroxyvitamin-D [25(OH)D] levels and uncontrolled diabetes among the Prospective-Epidemiological-Research-Studies-of-the-Iranian-Adults (PERSIAN) Guilan-Cohort-Study (PGCS) population with diabetes. Methods In this cross-sectional study, 603 adults with diabetes mellitus were recruited. Fasting blood glucose (FBS), glycated hemoglobin (HbA1c), and serum 25(OH)D levels were measured using standardized laboratory methods. Controlled diabetes was defined as FBS ≤130 mg/dL and HbA1c <7%, while uncontrolled diabetes was defined as FBS >130 mg/dL or HbA1c ≥7%. Logistic regression analyses were performed to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for uncontrolled diabetes across vitamin D status categories. Results The mean serum 25(OH)D level among participants was 22.7 ± 13.8 ng/mL; 21.4% were vitamin D–deficient, 26.2% insufficient, and 52.4% sufficient. Overall, 53.9% of diabetic patients had uncontrolled diabetes. Median 25(OH)D levels were significantly lower in patients with uncontrolled diabetes compared to those with controlled diabetes (19.5 [11.6–28.5] vs. 20.7 [13.2–32.0] ng/mL, P = 0.032). In the unadjusted model, vitamin D deficiency was associated with increased odds of uncontrolled diabetes (OR = 1.53, 95% CI: 1.01–2.33, P = 0.046); however, this association lost significance after adjustment for demographic factors and supplement use (adjusted OR = 1.42, 95% CI: 0.91–2.22, P = 0.125). Conclusion Vitamin D deficiency was associated with uncontrolled diabetes only in unadjusted analyses, and this relationship was attenuated after adjustment for confounding factors. Further prospective studies are needed to clarify this association.