Continued smoking exacerbates but cessation ameliorates progression of early type 2 diabetic nephropathy

We tested the hypothesis that continued cigarette smoking exacerbates and its cessation ameliorates progression of the early nephropathy of type 2 diabetes mellitus (DM2) from microalbuminuria to macroalbuminuria.

We recruited 91 DM2 subjects with microalbuminuria, 39 nonsmokers and 52 smokers. Smokers underwent smoking cessation intervention with 11 of the 52 smokers quitting, yielding 3 groups: nonsmokers (NS, n = 39), continued smokers (S, n = 41), and quitting smokers (Quit, n = 11), all on angiotensin converting enzyme inhibition (ACEI), treated toward recommended BP and glycemic targets, and followed prospectively for 5 years. Subjects had yearly measurements of estimated glomerular filtration rate (eGFR) and albumin (mg)-to-creatinine (g) ratios (alb/cr) in spot morning urines. Comparison of changes in characteristics was done using analysis of variance, with all pair wise multiple comparison procedure at alpha = 0.05.

Although average urine alb/cr was not different among groups at recruitment, 7 of the 41 S (17%) but none of the 50 NS or Quit progressed to macroalbuminuria (P < 0.003). eGFR decline rate was faster in S (-1.79 +/- 0.35 mL/min/yr) than in NS or Quit (-1.30 +/- 0.43 and -1.54 +/- 0.37 mL/min/yr, respectively, P < 0.001). Multivariate analysis revealed smoking to be the only measured baseline factor that influenced eGFR decline rate (P < 0.041).

Smoking exacerbates progression of early to advanced DM2 nephropathy and its cessation is an effective kidney-protective intervention in the early nephropathy of DM2.