Longitudinal associations of loneliness with mental ill-health, physical ill-health, lifestyle factors and mortality in ageing adults in Thailand

OBJECTIVES: The aim of this study was to assess the longitudinal association between loneliness, mental and physical ill-health indicators, lifestyle factors and mortality among middle-aged and older adults in Thailand. METHODS: We analyzed prospective cohort data of participants 45 years and older from three consecutive waves in 2015 (n = 5616), 2017 (n = 3600), and in 2020 (n = 2863) of the Health, Aging and Retirement in Thailand (HART) study. Loneliness was assessed with a single item. To assess the longitudinal associations between loneliness and health outcomes between 2015 (baseline), 2017 (first follow-up) and 2020 (second follow-up), we conducted Generalized Estimating Equations analysis (GEE). RESULTS: The proportion of loneliness was 21.6% in 2015, 23.8% in 2017 and 21.3% in 2020. In the adjusted GEE logistic regression model, loneliness was positively associated with mental ill-health (poor self-rated mental health status, poor quality of life/happiness, depressive symptoms, and insomnia symptoms), physical ill-health (poor self-rated physical health status, hypertension, kidney disease, osteoporosis, and ADL disability), and lifestyle factors (physical inactivity, and having underweight). Furthermore, in adjusted Cox proportional hazards regression, loneliness was associated with mortality. In adjusted logistic regression, compared to without loneliness in all three study waves, having loneliness in one wave and/or two to three waves was positively associated with incident mental ill-health (incident poor self-rated mental health status, incident poor quality of life/happiness, incident depressive symptoms, and incident insomnia symptoms), incident physical ill-health (incident poor self-rated physical health status, incident diabetes, incident kidney disease, and incident ADL disability), and incident lifestyle factors (having incident underweight). CONCLUSION: We found that loneliness was associated with several mental and physical ill-health indicators, lifestyle factors and mortality. Enhanced screening and treatment of loneliness may reduce mental and physical ill-health indicators in Thailand. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12888-023-05263-0.