The role of cigarette smoking on new-onset of chronic kidney disease in a Japanese population without prior chronic kidney disease: Iki epidemiological study of atherosclerosis and chronic kidney disease (ISSA-CKD).

BACKGROUND: Studies regarding harmful effects of smoking on the new-onset of chronic kidney disease (CKD) have been limited. Thus, we collected and retrospectively studied 8 years of data from the annual health check-ups of the residents in Iki City (Nagasaki Prefecture, Japan). METHODS: From 2008 to 2016, 4540 adults were enrolled in the study. Information on smoking habits was obtained via a self-reported questionnaire. New-onset CKD was defined as a reduction of the estimated globular filtration rate (eGFR) to less than 60 mL/min/1.73 m2 and/or new-onset proteinuria during the follow-up examinations. RESULTS: During an average follow-up of 4.6 years, proteinuria developed in 218 people (10.4 per 1000 person-years) and eGFR decline to less than 60 mL/min/1.73 m2 was confirmed in 594 people (28.3 per 1000 person-years) including 53 who showed both proteinuria and eGFR reduction (2.8 per 1000 person-years). In terms of proteinuria, current smokers showed a higher incidence than non-smokers (14.1 and 9.17 per 1000 person-years, respectively, p = 0.001), and a significantly high hazard ratio (HR) of 1.39 with a 95% CI of 1.01-1.92 in multivariable Cox's proportional-hazard analyses. The tendency was more drastic among younger participants (p = 0.015 for trend): current smokers who were < 50 years old had a significantly higher HR of 2.55 with a 95% CI of 1.01-6.45 (p = 0.004) than non-smokers. CONCLUSIONS: Smoking significantly increased the risk for new-onset of CKD based on proteinuria development in a Japanese population without CKD, and the association was more predominant in the younger population.