Cigarette Smoking Is Associated With Low Glomerular Filtration Rate in Male Patients With Type 2 Diabetes : Response to De Cosmo et al.

We read with interest the article by De Cosmo et al. (1) in the recent issue of Diabetes Care. The authors concluded from their cross-sectional data that cigarette smoking enhanced the risk of renal dysfunction in patients with type 2 diabetes despite their failure to demonstrate a significant dose effect; i.e., a relationship between the number of cigarettes smoked per day and the progression of nephropathy. While the authors suggested that these somewhat conflicting findings may have been due to indication bias, we would like to respectfully offer another explanation—that exclusion of ex-smokers from the analysis accounted for the negative dose effect. Sawicki et al. (2) reported that pack-years of cigarettes smoked was a dose-dependent risk factor for the progression of nephropathy in type 1 diabetic patients. Their prospective data demonstrated that the progression of nephropathy was statistically less common in individuals who never smoked compared with current smokers, with the values for ex-smokers being somewhere in the middle of these two groups. In addition, two prospective studies (3,4) in type 2 diabetic patients reported that those who were current or ex-smokers were at a significantly elevated risk of developing nephropathy. These studies strongly suggest that the inclusion of ex-smokers is imperative when evaluating a diabetic patient’s risk of nephropathy.