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

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