Background: Proteinuria is a significant risk factor for end-stage renal disease. Previous evidence suggested that smoking and obesity increase the risk of proteinuria. However, it is unclear whether these risk factors predict the development of proteinuria independently of hypertension and diabetes mellitus. The aim of this study was to analyze the effects of obesity and smoking on the development of proteinuria in a screened cohort of subjects with normal kidney function.
Methods: A total of 5403 subjects (3403 men and 2000 women) who participated in the 1997 and 1999 health screening examinations in Okinawa Japan, and who were normal renal function (serum creatinine < or =1.2 mg/dL in men, < or =1.0 mg/dL in women) and negative proteinuria by dipstick examination in 1997 were eligible for study. Logistic analysis was used to examine the relation between the baseline state of smoking or obesity in 1997, and the development of proteinuria in 1999, adjusted for age, sex, and other confounding factors.
Results: Proteinuria developed in 5.8% of participants (6.7% in men, 4.4% in women; dipstick score, 1+ in 277, 2+ in 37, and > or =3+ in 4 participants). The incidence of proteinuria was positively associated with the number of cigarettes smoked per day (P = 0.04), and a body mass index (P < 0.0001) at baseline. Analysis showed that the relative risk (95% confidence interval) of developing proteinuria was 1.32 (1.00 to 1.74), P = 0.04 for cigarette smoking, 1.45 (1.13 to 1.86), P = 0.002 for obesity, 1.56 (1.19 to 2.06), P = 0.001 for hypertension, and 2.27 (1.55 to 3.32), P < 0.0001 for diabetes mellitus. Stratified with men and women, the relative risk was 1.28 (0.96 to 1.72), P = 0.09 for smoking, and 1.60 (1.19 to 2.14), P = 0.001 for obesity in men; the relative risk was 1.30 (0.44 to 3.80), P = 0.62 for smoking, and 1.04 (0.63 to 1.72), P = 0.87 for obesity in women.
Conclusions: Hypertension and diabetes mellitus were superior to smoking and obesity in predicting the development of proteinuria in all subjects. Stratified with men and women, obesity was a significant risk factor for the development of proteinuria independently of both hypertension and diabetes mellitus in men. The risk of developing proteinuria also tended to be increased with cigarette smoking in men. Smoking and obesity in women were not significant in this data set.