Association of combined nighttime – midday napping patterns with possible sarcopenia among older Chinese adults: a cross-sectional analysis of CHARLS

Objective To investigate the association between combined nighttime and midday napping patterns and possible sarcopenia in the Chinese elderly population to provide evidence for developing targeted sleep health management strategies.Method This study use data from the 2015 China Health and Retirement Longitudinal Study (CHARLS) and included 7,003 elderly participants (≥60 years). Possible sarcopenia was defined according to the Asian Working Group for Sarcopenia 2019 consensus (AWGS 2019). The dose-response relationship between sleep duration and possible sarcopenia was analyzed using a Restricted Cubic Spline (RCS) model. Based on the RCS results, nighttime sleep duration was categorized as short (<6 h), medium (6-8 h), or long (>8 h), and nap duration was categorized as none (=0 min), short (>0-30 min), or long (>30 min). These categories were combined to construct nine distinct sleep patterns. A multivariate logistic regression model was employed to analyze the joint effects of these sleep patterns on possible sarcopenia. A sensitivity analysis was conducted among older adults with normal total sleep duration to assess the independent association of sleep patterns. Stratified analyses by sex and age were conducted to explore the associations between sleep patterns and possible sarcopenia across different subpopulations.Results The prevalence of possible sarcopenia in the study population was 39.60%. A U-shaped association was observed for both nighttime sleep duration and total sleep duration with possible sarcopenia, while an inverted L-shaped association was found for nap duration. After adjusting for covariates, compared to the reference group with "medium nighttime sleep + short midday nap", individuals with the "short nighttime sleep + no midday nap" pattern exhibited a significantly higher odds of possible sarcopenia (OR = 1.629, 95% CI: 1.302-2.036). Furthermore, the combinations of "short nighttime sleep + long midday nap", "long nighttime sleep + no midday nap", and "long nighttime sleep + long midday nap" were also significantly associated with possible sarcopenia. The sensitivity analysis revealed that the "long nighttime sleep + no midday nap" pattern remained significantly associated with possible sarcopenia (OR = 1.770, 95% CI: 1.191-2.630, P = 0.005) among older adults with normal total sleep duration (6-9 h). Stratified analyses revealed that these adverse associations between specific sleep patterns and possible sarcopenia remained significant among females and individuals aged below 80 years.Conclusion Nighttime sleep duration demonstrated a dominant role within the joint sleep patterns, while the association of napping variability was primarily evident under conditions of non-medium (i.e., either short or long) nighttime sleep duration. Even with normal total sleep duration, the particular sleep structure of "long nighttime sleep without any midday napping" was associated with possible sarcopenia. Overall, a comprehensive assessment of combined nighttime-midday sleep patterns is instrumental in identifying older adults at elevated risk associated with sarcopenia.

研究目的：本研究旨在探讨中国老年人群夜间与日间午睡联合睡眠模式与可能肌少症（possible sarcopenia）的关联，为制定针对性睡眠健康管理策略提供循证依据。
研究方法：本研究采用2015年中国健康与养老追踪调查（CHARLS）的数据，共纳入7003名年龄≥60岁的老年参与者。可能肌少症的定义参照《亚洲肌少症工作组2019共识》（AWGS 2019）。采用限制性立方样条（Restricted Cubic Spline, RCS）模型分析睡眠时长与可能肌少症之间的剂量-反应关系。基于RCS模型结果，将夜间睡眠时间划分为短时长（<6小时）、中时长（6~8小时）及长时长（>8小时），午睡时长则划分为无午睡（=0分钟）、短午睡（0~30分钟）及长午睡（>30分钟）。将上述分类组合后，共构建9种不同的睡眠模式。采用多因素logistic回归模型分析上述睡眠模式对可能肌少症的联合效应。在总睡眠时间正常的老年人群中开展敏感性分析，以评估睡眠模式的独立关联。按性别与年龄进行分层分析，以探讨不同亚群中睡眠模式与可能肌少症的关联。
研究结果：本研究人群中可能肌少症的患病率为39.60%。夜间睡眠时间及总睡眠时间与可能肌少症均呈U型关联，而午睡时长则呈倒L型关联。校正混杂因素后，以“夜间中时长睡眠+短时午睡”为参照组，“夜间短时长睡眠+无午睡”模式人群的可能肌少症患病风险显著升高（OR=1.629，95%CI：1.302~2.036）。此外，“夜间短时长睡眠+长午睡”“夜间长时长睡眠+无午睡”及“夜间长时长睡眠+长午睡”这三种组合模式也与可能肌少症存在显著关联。敏感性分析结果显示，在总睡眠时间正常（6~9小时）的老年人群中，“夜间长时长睡眠+无午睡”模式仍与可能肌少症存在显著关联（OR=1.770，95%CI：1.191~2.630，P=0.005）。分层分析结果显示，特定睡眠模式与可能肌少症的上述不良关联在女性及80岁以下人群中仍具有统计学意义。
研究结论：夜间睡眠时间在联合睡眠模式中发挥主导作用，而午睡的影响主要体现在夜间睡眠时长非中等（即过短或过长）的情况下。即使总睡眠时间处于正常范围，“夜间长时长睡眠且无午睡”这一特殊睡眠结构仍与可能肌少症相关。总体而言，全面评估夜间与日间午睡的联合睡眠模式，有助于识别肌少症风险升高的老年人群。