A Systematic Review and Meta-Analysis of Longitudinal Studies Exploring the Link Between Physical Inactivity and Indicators of Childhood Overweight/Obesity and Metabolically Unhealthy Obesity Risk in Western Countries

BACKGROUND: Physical inactivity (PI) is a major contributor to adiposity and cardiometabolic morbidity. OBJECTIVE: To synthesize evidence of the association between PI and childhood overweight/obesity (OV/OB) and metabolically unhealthy obesity (MUO; OB accompanied by cardiometabolic abnormalities) risk. METHODS: A systematic review and meta-analysis of prospective epidemiological studies and randomized controlled trials (RCTs) was performed following PRISMA guidelines (PROSPERO ID: CRD42023482960). Studies conducted in Western countries with 2-19-year-old participants, PI-related exposures (time/frequency of engagement in various sedentary behaviors) and interventions (targeting PI reduction), OV/OB-/MUO-related outcomes and ≥ 12-month follow-up were extracted from PubMed and Scopus (publication timeframe: 01/01/2013-30/06/2024). Study quality was assessed through risk of bias (RoB). RESULTS: Among 86 prospective epidemiological studies with OV/OB-related outcomes (42% high-RoB), PI was evaluated objectively (accelerometry) in 34 and subjectively (questionnaires) in 57 (29% and 68% reported detrimental associations, respectively). In random-effects meta-analysis, subjectively-assessed total screen time was positively associated with body mass index (BMI) [n = 4; beta (95%CI): 0.116 (0.037, 0.195) kg/m2] and BMI z-score [n = 8; beta (95%CI): 0.032 (0.002, 0.063)], while television viewing was positively associated with BMI [n = 3; beta (95%CI): 0.227 (0.025, 0.428) kg/m2], BMI z-score [n = 4; beta (95%CI): 0.042 (0.007, 0.077)] and OV/OB incidence [n = 5; logRR (95%CI): 0.089 (0.044, 0.133)]. The sole RCT (low-RoB) indicated a beneficial effect of reducing sedentariness on anthropometric indices. Two prospective epidemiological studies (high-RoB) suggested positive associations between subjectively-assessed total screen time and MUO-related outcomes. CONCLUSIONS: Screen time is positively associated with indicators of childhood OV/OB risk, while limited evidence also supports its detrimental role in MUO.