Social isolation, loneliness and sarcopenia: insights from three longitudinal ageing cohorts of 22 countries

BACKGROUND: Sarcopenia is a major age-related health condition that remains inadequately recognised as a public health concern. While previous studies have primarily focused on physical risk factors, limited evidence exists regarding the distinct contributions of social isolation and loneliness to sarcopenia development. This study investigates the individual and joint effects of social isolation and loneliness on sarcopenia. METHODS: A total of 87 205 middle-aged and older adults from the Health and Retirement Study, the Survey of Health, Ageing and Retirement in Europe, and the China Health and Retirement Longitudinal Study were analysed. Sarcopenia was classified as a state of sarcopenia or severe sarcopenia. Social isolation was assessed based on the number of adverse social events. Loneliness was measured through the revised UCLA Loneliness Scale and the Center for Epidemiologic Studies Depression scale. Cox regression was used, adjusting for sociodemographic covariates, and random-effect meta-analysis was used to pool country-specific estimates. Subgroup analyses were conducted on all covariates. RESULTS: Social isolation and loneliness were individually and jointly associated with a higher risk of incident sarcopenia, persistent sarcopenia and worsening sarcopenia states. A synergistic effect was found only for the consistent coexistence of both conditions from baseline to the end of the follow-up. Subgroup analyses demonstrated a stronger association among middle-aged participants without chronic diseases. CONCLUSION: Our findings suggest social isolation and loneliness should be treated as differentiated measures of social connections in future interventions or studies. Interventions may be more worthwhile before people are exposed to multiple risk factors.