Smoking and progression of diabetic nephropathy in type 1 diabetes

OBJECTIVE - Cigarette smoking contributes to development of diabetic nephropathy. However, long-term studies on the effect of smoking on decline in kidney function in diabetic nephropathy are lacking, We assessed the impact of smoking on progression of diabetic nephropathy in type I diabetic patients enrolled in a prospective observational cohort study started in 1983. RESEARCH DESIGN AND METHODS - We identified all albuminuric type I diabetic patients (n = 301) followed for at least 3 years, median (range) 7 years (3-14), who under-went at least yearly measurement of glomerular filtration rate (GFR) by the Cr-51-EDTA plasma clearance technique (n = 8, range 3-24). In total, 192 men and 109 women were included (age [mean +/- SD] 36 +/- 11 years, duration of diabetes 22 +/- 8 years); 271 patients were treated with antilrypertensive drugs, predominantly ACE inhibitors in 179 patients. Patients were classified as smokers if they smoked more than one cigarette per day during a portion of or the entire observation period. Blood pressure, albuminuria, HbA(1c), and serum cholesterol were measured every 3-4 months during the study. RESULTS - In all 301 patients, the mean (SE) rate of decline in GFR (DeltaGFR) was 4.0 (0.2) ml . min(-1) . year(-1) during the investigation period. No difference in DeltaGFR was demonstrated between nonsmokers (n = 94), DeltaGFR 4.5 (0.4), ex-smokers (n = 31), DeltaGFR 3.1 (0.7), and smokers (n = 176), DeltaGFR 3.9 (0.3) ml . min(-1) . year(-1), respectively (NS). Adjustment for other risk factors for progression of diabetic nephropathy did not alter the results: smoking was not associated with AGFR, whereas blood pressure, albuminuria, HbA(1c), and serum cholesterol were demonstrated to be independent progression promoters. CONCLUSIONS - in our study, smoking was not associated with decline in kidney function in type I diabetic patients with diabetic nephropathy.