Smoking and progression of diabetic nephropathy in patients with type 1 diabetes

Aims To evaluate the effect of cumulative smoking on the development of diabetic nephropathy. Methods Study included 3613 patients with type 1 diabetes, participating in the Finnish Diabetic Nephropathy Study. The 12-year cumulative risk of microalbuminuria, macroalbuminuria and end-stage renal disease (ESRD) was estimated for current, ex- and nonsmokers. Cox regression analyses, with multivariable adjustments for other risk factors for diabetic nephropathy, were used to evaluate the risk at different stages of diabetic nephropathy based on the cumulative amount of smoking in pack-years. Results The 12-year cumulative risk of microalbuminuria was 18.9 % (95 % CI 14.6–23.0, P < 0.0001) for current smokers and 15.1 % (10.3–19.6, P = 0.087) for ex-smokers, compared with 10.0 % (7.8–12.1) for nonsmokers. The corresponding risks of macroalbuminuria were 14.4 % (95 % CI 10.8–17.9, P < 0.0001), 6.1 % (3.5–8.6, P = 0.082) and 4.7 % (3.0–6.4), respectively. The 12-year cumulative risk of ESRD was 10.3 % (95 % CI 8.4–12.4, P < 0.0001) for current smokers and 10.0 % (7.9–12.3, P < 0.0001) for ex-smokers, compared with 5.6 % (4.6–6.7) for nonsmokers. In the current smokers, one pack-year increased the risk of macroalbuminuria with a HR of 1.025 (1.010–1.041) and the risk of ESRD with a HR of 1.014 (1.001–1.026) compared with nonsmokers, in the fully adjusted model. In the ex-smokers, the risk of macroalbuminuria and ESRD was no different from the risk in nonsmokers after multivariable adjustment. Conclusions Current smoking is a risk factor for the progression of diabetic nephropathy and the risk increases with the increasing dose of smoking. Ex-smokers seem to carry a similar risk of progression of diabetic nephropathy as nonsmokers.