Supplementary Material for: Association of self-reported nighttime sleep duration with chronic kidney disease: China Health and Retirement Longitudinal Study

Introduction: The cohort study aimed to assess the association of nighttime sleep duration and the change in nighttime sleep duration with chronic kidney disease (CKD), and whether the association between nighttime sleep duration and CKD differed by daytime napping.
Methods: This study included 11677 individuals of the China Health and Retirement Longitudinal Study (CHARLS) and used data from the 2011 baseline survey and four follow-up waves. Nighttime sleep duration was divided into three groups: short (<7h per night), optimal (7-9h), and long nighttime sleep duration (>9h). Daytime napping was divided into two groups: no nap, with a nap. We used Cox proportional hazards model to examine the effect of nighttime sleep duration at baseline and change in nighttime sleep duration on incident CKD, and a joint effect of nighttime sleep duration and nap time on onset CKD.
Results: With a follow-up of 7 years, the incidence of CKD among those with short, optimal and long nighttime sleep duration was 9.89, 6.75, and 9.05 per 1000 person-years, respectively. Compared to individuals with optimal nighttime sleep duration, short nighttime sleepers had a 44% higher risk of onset CKD (hazard ratio [HR]: 1.44, 95% Confidence intervals [CIs]:1.21-1.72). Compared to participants with persistent optimal nighttime sleep duration, those with persistent short or long nighttime sleep duration had an increased risk of incident CKD (HR:1.44, 95%CI:1.15-1.80). We found a lower incidence of CKD in participants with short nighttime sleep duration and a nap (HR:0.74, 95%CI:0.60-0.93), compared to those with short nighttime sleep duration and no nap.
Discussion/Conclusion: Short nighttime sleep duration and persistent long or short nighttime sleep duration were associated with a higher risk of onset CKD. Keeping persistent optimal nighttime sleep duration may help reduce CKD risk later in life. Daytime napping may be protective against onset CKD.

研究背景：本队列研究旨在探讨夜间睡眠时长及其变化与慢性肾脏病（chronic kidney disease, CKD）的关联，并分析夜间睡眠时长与CKD的关联是否因日间午睡状态存在差异。
研究方法：本研究纳入中国健康与养老追踪调查（China Health and Retirement Longitudinal Study, CHARLS）的11677名受试者，采用2011年基线调查及四轮随访的数据。将夜间睡眠时长分为三组：短睡眠（每晚<7小时）、最优睡眠（7~9小时）及长睡眠（每晚>9小时）；将日间午睡分为两组：无午睡、有午睡。本研究采用Cox比例风险模型（Cox proportional hazards model），分析基线夜间睡眠时长及夜间睡眠时长变化对新发CKD的影响，并探究夜间睡眠时长与午睡的联合效应对CKD发病的作用。
研究结果：经过7年随访，短睡眠、最优睡眠及长睡眠组人群的CKD发病率分别为每1000人年9.89、6.75及9.05例。与最优睡眠时长的受试者相比，短睡眠者的CKD发病风险升高44%（风险比（hazard ratio, HR）：1.44，95%置信区间（confidence interval, CI）：1.21~1.72）。与持续保持最优夜间睡眠时长的受试者相比，持续短睡眠或持续长睡眠者的新发CKD风险均升高（HR：1.44，95%CI：1.15~1.80）。与短睡眠且无午睡的受试者相比，短睡眠且有午睡的受试者CKD发病率更低（HR：0.74，95%CI：0.60~0.93）。
讨论与结论：夜间睡眠时长过短，以及持续长睡眠或持续短睡眠，均与CKD发病风险升高相关。持续保持最优夜间睡眠时长，有助于降低晚年罹患CKD的风险。日间午睡或可对CKD发病起到保护作用。