Association Between Vitamin D Deficiency and Glycemic Control in Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study.

Original Article

Abstract

Background: Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and progressive β-cell dysfunction, resulting in chronic hyperglycemia. Poor glycemic control increases the risk of microvascular and macro vascular complications. Vitamin D deficiency has emerged as a potential modifiable factor influencing glucose metabolism; however, evidence regarding its association with glycemic control remains inconsistent.

Objectives: To evaluate the association between serum vitamin D deficiency and glycemic control (HbA1c) among patients with type 2 diabetes mellitus attending a tertiary care hospital and to determine whether vitamin D deficiency is independently associated with poor glycemic control.

Methods: This cross-sectional study included 100 adults with T2DM attending the outpatient Department of Pulmonology, PIMS Islamabad from jan 2025 june 2025. Demographic, clinical, anthropometric, and laboratory data were collected. Serum glycated hemoglobin (HbA1c) was measured using high-performance liquid chromatography (HPLC), while serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured using chemiluminescent immunoassay (CLIA). Vitamin D deficiency was defined as serum 25(OH)D <20 ng/mL.Data were analyzed using IBM SPSS Statistics version 27.0. Continuous variables were compared using the independent-samples t-test, categorical variables using the Chi-square test, Pearson's correlation coefficient was used to assess the relationship between serum vitamin D and HbA1c, and multivariable logistic regression analysis was performed to identify independent predictors of poor glycemic control. A p-value <0.05 was considered statistically significant.

Results: Vitamin D deficiency was identified in 62 (62%) participants, whereas 38 (38%) had sufficient serum vitamin D levels. (≥20 ng/mL). Mean HbA1c was significantly higher among vitamin D-deficient participants than non-deficient participants (8.9 ± 1.3% vs. 7.5 ± 1.2%; p<0.001). Poor glycemic control (HbA1c ≥7%) was more frequent in vitamin D-deficient patients (81.3% vs. 52.8%; p=0.003). Multivariable logistic regression demonstrated that vitamin D deficiency was independently associated with poor glycemic control (adjusted OR 3.21; 95% CI 1.36–7.59; p=0.008)

Conclusion: Vitamin D deficiency is highly prevalent among patients with T2DM and is independently associated with poor glycemic control. Prospective studies and randomized controlled trials are warranted to determine whether correction of vitamin D deficiency improves long-term glycemic outcomes.