Smoking and progression of diabetic nephropathy in type 1 diabetes

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 1 diabetic patients enrolled in a prospective observational cohort study started in 1983.

We identified all albuminuric type 1 diabetic patients (n = 301) followed for at least 3 years, median (range) 7 years (3-14), who underwent at least yearly measurement of glomerular filtration rate (GFR) by the (51)Cr-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 antihypertensive 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.

In all 301 patients, the mean (SE) rate of decline in GFR (deltaGFR) was 4.0 (0.2) mlx min(-1) x year(-1) during the investigation period. No difference in Delta GFR 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 x min(-1) x year(-1), respectively (NS). Adjustment for other risk factors for progression of diabetic nephropathy did not alter the results: smoking was not associated with deltaGFR, whereas blood pressure, albuminuria, HbA(1c), and serum cholesterol were demonstrated to be independent progression promoters.

In our study, smoking was not associated with decline in kidney function in type 1 diabetic patients with diabetic nephropathy.