Supplementary Material for: Association between Sleep Duration and Incident Chronic Kidney Disease: A Population-Based Cohort Analysis of the NAGALA Study

Background: The duration of sleep might be a risk factor for chronic kidney disease (CKD). We investigated the relationship between sleep duration and incident CKD. Methods: In this retrospective cohort study of 7,752 men and 6,722 women, we divided the subjects into 4 groups according to sleep duration, i.e., those whose reported regular sleep duration was <6 h (the “<6 h group”), those whose sleep duration was >6 but <7 h (the “6 to <7 h group”), those with a sleep duration of 7 to <8 h (the “7 to <8 h group”), and those with ≥8 h sleep (the “≥8 h group”). CKD was defined as the presence of proteinuria and/or an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2. The HR of the 4 groups for incident CKD were calculated with a Cox proportional hazards model, with the 7 to <8 h group set as the reference. Results: Incident CKD was detected in 1,513 (19.5%) men and 688 (10.2%) women over the median follow-up period of 7.0 (3.3–11.9) years in the men and 6.7 (3.1–10.8) years in the women. There was no association between sleep duration and incident CKD in the women. In the men, the HR of incident CKD was 0.54 (95% CI 0.45–0.64, p < 0.001) in the <6 h group, 0.73 (95% CI 0.66–0.82, p < 0.001) in the 6 to <7 h group, and 0.93 (95% CI 0.78–1.11, p = 0.433) in the ≥8 h group. Conclusion: The risk of incident CKD is lowest in those who sleep <6 h. We revealed that the risk of incident CKD is lowest in those who sleep <6 h among apparently healthy men.