Diabetes Duration Is Associated with Declining Kidney Function: eGFR and CKD Burden Across Duration

<b>Background:</b> Diabetic kidney disease is a major complication of type 2 diabetes mellitus (T2DM) and a leading cause of chronic kidney disease (CKD) worldwide. While diabetes duration is often considered a marker of cumulative metabolic exposure, its independent contribution to renal decline beyond aging and hypertension remains incompletely defined. <b>Methods:</b> We conducted a cross-sectional study including 250 adults with T2DM. Diabetes duration was analyzed both as a continuous variable and across four predefined strata (0-4, 5-9, 10-14, and ≥15 years). The primary endpoint was estimated glomerular filtration rate (eGFR), analyzed as a continuous outcome. Functional CKD was defined as eGFR < 60 mL/min/1.73 m². Linear and logistic regression models were constructed in unadjusted and adjusted forms (age, sex, BMI, hypertension, HbA1c). A sensitivity analysis modeling duration per 5-year increase was performed. <b>Results:</b> Mean eGFR declined significantly across duration strata (82.45, 84.27, 78.72, and 61.57 mL/min/1.73 m², respectively; <i>p</i> < 0.001). The prevalence of functional CKD increased markedly in patients with ≥15 years of diabetes (54.2%) compared with shorter-duration groups (~15-18%; <i>p</i> < 0.001). In linear regression, each additional year of diabetes was associated with a 1.32 mL/min/1.73 m² decline in eGFR (<i>p</i> < 0.001), remaining significant after adjustment (β = -0.85; <i>p</i> < 0.001). In logistic regression, each additional year was associated with a 10.7% increase in adjusted odds of CKD (OR = 1.11; 95% CI 1.04-1.17; <i>p</i> < 0.001). Each 5-year increment conferred a 66% increase in adjusted CKD risk (OR = 1.66; 95% CI 1.25-2.21; <i>p</i> < 0.001). Patients with ≥15 years of diabetes had nearly fourfold higher adjusted odds of CKD compared with those with 0-4 years (OR = 3.90; 95% CI 1.42-10.75; <i>p</i> = 0.008). <b>Conclusions:</b> Diabetes duration is strongly and independently associated with declining kidney function. Prolonged disease exposure confers a substantial increase in CKD risk, even after adjustment for age, hypertension, and metabolic factors. These findings highlight the progressive nephrotoxic impact of cumulative hyperglycemic exposure and underscore the need for early and sustained nephroprotective strategies in T2DM.