Effects of current smoking and smoking discontinuation on renal function and proteinuria in the general population

Background. Smoking may adversely affect the progression of renal diseases. However, it is unknown whether smoking affects renal function in subjects without nephropathy. Methods. In 1998, 28,409 volunteers from the general population were examined at the Institut Regional pour la Sante (IRSA). Renal function was estimated with creatinine clearance using the Cockcroft formula. Dipstick proteinuria was assessed on an overnight urine sample by a trained technician. Results. Adjusted creatinine clearance was higher in current smokers than in former smokers and never smokers (100.6 +/- 13.6 vs. 98.8 +/- 13.9 mL/min/1.73 m(2), P < 0.0001, and vs. 98.5 +/- 14.0 mL/min/1.73 m(2), P < 0.0001, respectively). This difference was predominant in men and weak in women, and was associated with the number of cigarettes smoked daily. The slope of the projected age-related decline in the creatinine clearance accelerated with age, but it was similar in current smokers, former smokers, and never smokers. Creatinine clearance was associated with a relative risk of proteinuria [for each mL/min/1.73 m(2), the relative risk was 1.007 (95% CI, 1.000 to 1.015), P = 0.056, for 1+ or higher proteinuria; and 1.018 (1.004 to 1.030), P = 0.0078, for 2+ or higher proteinuria]. Current and former smokers had a marked risk of 2 or higher proteinuria [adjusted RR (95% CI), 3.26 (1.66 to 6.80), P = 0.0009, and 2.69 (1.24 to 5.99), respectively, P = 0.013, vs, never smoking], which was independent of the daily or cumulative cigarette consumption. Conclusions. In the general population, smokers do not exhibit lower creatinine clearance than never smokers. In fact, creatinine clearance is slightly higher in current smokers at least in men, even when normotensive and hypertensive subjects are analyzed separately, but the difference is small, especially in women. This effect seems reversible upon smoking discontinuation. Chronic smoking results in a marked risk of irreversible proteinuria that may occur despite moderate smoking.