Supplementary Material for: The effect of social isolation on sarcopenia: a longitudinal study among the middle-aged and older population in China

Introduction: Although social isolation is associated with premature death and somatic and mental diseases, evidence of its long-term effect on sarcopenia is scarce. This study aimed to examine the longitudinal association between social isolation and possible sarcopenia. Methods: We extracted baseline and four-year follow-up data from the China Health and Retirement Longitudinal Study and included participants aged 45 years or above. Social isolation was measured by factors including living alone, marital status, frequency of contact with adult children and friends, and participation in social activity. The change in social isolation from baseline to follow-up was classified into stable, progressive, and regressive groups. Possible sarcopenia was detected using the handgrip strength and five-time chair stand test. Using mixed effects logistic regression, we studied the effect of baseline isolation and the change in isolation status on possible sarcopenia at a four-year follow-up. Results: A total of 5289 participants aged 45 to 90 years and without possible sarcopenia at baseline were included. After four years, possible sarcopenia was detected in 21.7% (1146/5289) of the participants. Compared with the low social isolation group, the middle (OR=1.53, 95% confidence interval [CI]=1.16~2.04, p=0.003) and high social isolation groups (OR=1.65, 95% CI=1.26~2.18, p<0.001) were associated with a higher risk of possible sarcopenia. Being not married/cohabiting (OR=1.58, 95% CI=1.19~2.10, p=0.002), lack of contact with children (OR=1.86, 95% CI=1.21~2.85, p=0.004), and lack of social activities (OR=1.26, 95% CI=1.04~1.53, p=0.019) were associated with an increased risk of possible sarcopenia. Compared with the stable social isolation group, the progressive group was associated with a greater risk of possible sarcopenia (OR=1.51, 95% CI=1.17~1.95, p=0.001). Conclusions: Social isolation is associated with an increased risk of possible sarcopenia. Progressive social isolation further elevates the risk. The most vulnerable groups are middle-aged and older people who live alone, are not socially active, and lack contact with their children.引言：尽管社交孤立与过早死亡、躯体及精神疾病存在关联，但目前关于其对肌肉减少症(sarcopenia)长期影响的研究证据仍较为匮乏。本研究旨在探讨社交孤立与可能的肌肉减少症之间的纵向关联。 研究方法：本研究从中国健康与养老追踪调查中提取基线及四年随访数据，纳入年龄≥45岁的参与者。社交孤立通过独居情况、婚姻状况、与成年子女及朋友的接触频率、社会活动参与度等维度进行评估。将基线至随访阶段的社交孤立变化情况划分为稳定、进展性及消退性三组。可能的肌肉减少症通过握力测试及五次坐姿起立测试进行筛查。采用混合效应logistic回归模型，分析基线社交孤立水平及社交孤立状态变化对四年随访时可能的肌肉减少症的影响。 研究结果：本研究共纳入5289名年龄在45至90岁之间、基线无可能肌肉减少症的参与者。四年随访后，共计21.7%（1146/5289）的参与者被检出可能的肌肉减少症。与低社交孤立组相比，中社交孤立组（OR=1.53，95%置信区间[CI]=1.16~2.04，p=0.003）与高社交孤立组（OR=1.65，95% CI=1.26~2.18，p<0.001）的可能肌肉减少症发病风险均显著升高。未结婚/无同居伴侣（OR=1.58，95% CI=1.19~2.10，p=0.002）、缺乏与子女的接触（OR=1.86，95% CI=1.21~2.85，p=0.004）及较少参与社会活动（OR=1.26，95% CI=1.04~1.53，p=0.019）均与可能的肌肉减少症发病风险升高显著相关。与稳定社交孤立组相比，进展性社交孤立组的可能肌肉减少症发病风险更高（OR=1.51，95% CI=1.17~1.95，p=0.001）。 研究结论：社交孤立与可能的肌肉减少症发病风险升高显著相关，而进展性社交孤立会进一步加剧该风险。独居、社会参与度低及缺乏子女联系的中老年群体为该关联的高风险人群。