Leisure-time sedentary behavior and loneliness among 148,045 adolescents aged 12–15 years from 52 low- and middle-income countries

•Sedentary behavior and loneliness are highly prevalent among school going adolescents in low and middle income countries.•Being sedentary for ≥8h/day is associated with a twice as high risk for feeling lonely compared to being sedentary for 8 h/day sedentary. Compared to those who engage in less than 1 h of LTSB per day, the OR (95%CI) of loneliness for 1–2 h/day, 3–4 h/day, 5–8 h/day and >8 h/day were 1.00 (0.91–1.11), 1.29 (1.15–1.45), 1.37 (1.17–1.61), and 1.66 (1.39–1.99), respectively. The study is cross-sectional, therefore the directionality of the relationships cannot be deduced. Our data suggest that LTSB is associated with increased odds for feeling lonely in adolescence. Future longitudinal data are required to confirm/refute the findings to inform public health campaigns.