Association Between Vitamin D Status and Renal Impairment in Type 2 Diabetic Patients Treated with Metformin in N'Djamena (Chad)

Background and Objective: Vitamin D plays an important role in metabolic and renal health, and its deficiency has been linked to chronic kidney disease (CKD). This study evaluated the association between vitamin D deficiency and renal impairment among metformin-treated patients with Type 2 Diabetes Mellitus (T2DM) at the National Referral University Hospital of N'Djamena, Chad. Materials and Methods: A cross-sectional study was conducted from April to June 2025 among 88 adults with T2DM receiving metformin for at least six months. Serum 25-hydroxyvitamin D [25(OH)D], creatinine, albumin, glycated hemoglobin (HbA1c), fasting blood glucose, and estimated glomerular filtration rate (eGFR) were measured. Vitamin D deficiency was defined as 25(OH)D <20 ng/mL and renal impairment as eGFR <60 mL/min/1.73 m². Multivariate logistic regression identified factors associated with renal impairment. Results: Vitamin D deficiency and renal impairment were present in 35.2% and 30.7% of participants, respectively. Vitamin D-deficient patients had lower eGFR (p = 0.019), higher serum creatinine (p = 0.015), and lower albumin (p = 0.025). Vitamin D deficiency independently predicted renal impairment (AOR = 3.80, 95% CI: 1.40–10.20; p = 0.008), along with elevated HbA1c, fasting blood glucose, hypoalbuminemia, and serum creatinine. Conclusion: Vitamin D deficiency is common among metformin-treated patients with T2DM in Chad and is independently associated with renal impairment. Routine vitamin D and renal function assessment may improve early identification of patients at risk of diabetic kidney disease.