Influence of Smoking on Proteinuria and Change in eGFR; Its Relevance: A Longitudinal 8-year Follow Up Analysis

Abstract

Objective: To clarify the influence of smoking on proteinuria, and change in eGFR - its relevance based on an 8-year longitudinal analysis.

Methods: The subjects were 7,476 males (smokers 2,954, previous smokers 2,471, non-smokers 2,051) who were 35 – 65 years old, had a 0.56 – 1.03 mg/dL serum creatinine level at baseline, and had maintained a smoking habit over 8 years. Proteinuria was defined as 1+ or higher in the dipstick test. Percent change in eGFR in each year (PCG) and eGFR decline rate (GDR) were calculated for each subject using the ordinary-least-squares method.

Results: The hazard ratio of smoking to non-smoking for new-onset proteinuria was 1.4 in the non-proteinuria group at baseline. The incidence of proteinuria in smokers was higher than in non-smokers and previous smokers over the entire range of eGFR. Smoking, lower eGFR, elevation of blood pressure, glycemic status, BMI, and uric acid were independent risk factors for proteinuria. The average GDR was –0.48 mL/min/1.73 m²/year. GDR was greater in smokers and previous smokers with proteinuria, younger subjects, and subjects with a higher eGFR. Over 3 years, in subjects without proteinuria in the 1st year who developed proteinuria in the 2nd year, eGFR significantly decreased. In the 3rd year, eGFR recovered in those without proteinuria, while it decreased in those with proteinuria. Smoking, anti-diabetic treatment, and elevation of blood pressure and BMI were risk factors for the latter. The prevalences of –25% and +25% PCG were 2.7 and 6.6%, respectively. Smoking was a risk factor for –25% PCG.

Conclusion: Smoking is a risk-factor for proteinuria. Smokers and previous smokers with proteinuria had a greater GDR. Continuing proteinuria is suggestive of a future decline in eGFR.