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：尽管社交隔离与过早死亡、躯体及精神疾病存在关联，但目前关于其对肌肉减少症（sarcopenia）的长期影响的研究证据仍较为匮乏。本研究旨在探讨社交隔离与可能的肌肉减少症之间的纵向关联。
方法：本研究从中国健康与养老追踪调查（China Health and Retirement Longitudinal Study）中提取基线数据与四年随访数据，纳入年龄≥45岁的研究对象。社交隔离通过独居状态、婚姻状况、与成年子女及朋友的接触频率、社交活动参与情况等维度进行评估。将基线至随访阶段的社交隔离变化情况分为稳定组、进展组与缓解组。采用握力测试与五次坐站试验检测可能的肌肉减少症。通过混合效应logistic回归分析，探究基线社交隔离水平及隔离状态变化对四年随访时可能的肌肉减少症的影响。
结果：本研究共纳入5289名年龄介于45至90岁、基线时无可能肌肉减少症的参与者。经过四年随访，21.7%（1146/5289）的参与者被检出可能的肌肉减少症。与低社交隔离组相比，中社交隔离组（OR=1.53，95%置信区间[CI]=1.16~2.04，p=0.003）与高社交隔离组（OR=1.65，95% CI=1.26~2.18，p<0.001）的可能肌肉减少症发病风险显著升高。未结婚/同居（OR=1.58，95%置信区间[CI]=1.19~2.10，p=0.002）、缺乏与子女的接触（OR=1.86，95%置信区间[CI]=1.21~2.85，p=0.004）以及缺乏社交活动（OR=1.26，95%置信区间[CI]=1.04~1.53，p=0.019）均与可能的肌肉减少症发病风险升高存在关联。与稳定社交隔离组相比，进展组的可能肌肉减少症发病风险更高（OR=1.51，95%置信区间[CI]=1.17~1.95，p=0.001）。
结论：社交隔离与可能的肌肉减少症发病风险升高相关，且进行性加重的社交隔离会进一步提升该风险。独居、社交活动匮乏以及缺乏子女联系的中老年群体为该疾病的易感高风险人群。