Excessive Smart Device Use and Mental-Metabolic Health Risks in Middle-aged Adults: Evidence from the Korean National Health and Nutrition Examination Survey

Abstract Background Excessive smart device use has been increasingly associated with adverse mental and metabolic health outcomes, but data on middle-aged adults are limited. This study examined the associations between heavy smart-device use and mental health, metabolic health, and their combined risk among Korean adults aged 40–59 years. Methods Data from 3,079 adults from the 2021 and 2023 Korea National Health and Nutrition Examination Surveys were analyzed. Excessive smart device use was defined as at least 4 h per day. Mental health outcomes included high stress and depressive symptoms; metabolic health outcomes covered metabolic syndrome and phenotypes (metabolically healthy normal weight, metabolically healthy obesity, metabolically unhealthy normal weight, and metabolically unhealthy obesity). Participants were grouped by risk: no-risk, single-domain risk (mental or metabolic), and dual-domain risk. Analyses were stratified by sex, sleep duration, muscle-strengthening activity, and sedentary behavior, adjusting for demographic (age, sex, education, household income, marital status, employment) and lifestyle factors (smoking and alcohol use) using complex survey sampling. Results Excessive smart device users demonstrated increased risk of experiencing high stress (adjusted odds ratio [aOR]: 1.39; 95% confidence interval [CI]: 1.16–1.67), depressive symptoms (aOR: 1.60; 95% CI: 1.21–2.11), metabolic syndrome (aOR: 1.23; 95% CI: 1.02–1.50), metabolically healthy obesity (aOR: 1.30; 95% CI: 1.01–1.67), and metabolically unhealthy obesity (aOR: 1.42; 95% CI: 1.13–1.77). Furthermore, excessive smart device use was associated with elevated odds of single-domain risk (aOR: 1.30; 95% CI: 1.08–1.57) and dual-domain risk (aOR: 1.76; 95% CI: 1.36–2.27). Stratified analyses indicated that several associations achieved statistical significance only among subgroups characterized by inadequate or excessive sleep, insufficient muscle-strengthening activity, or prolonged sedentary behavior. Conclusions Excessive smart device use is associated with mental health issues, adverse metabolic profiles, and their co-occurrence. Public health interventions should incorporate assessments and management of digital device use, particularly for individuals with poor sleep, low physical activity, and prolonged sedentary time.