Associations of Mentally Active Versus Passive Sedentary Behavior with Smartphone Addiction in Adults

Background: Sedentary behavior (SB) has been linked to problematic smartphone use: however, whether different types of SB differentially relate to smartphone addiction risk remains unclear. This study aimed to examine the prevalence of smartphone addiction risk and the independent associations of mentally active and mentally passive SB—across total, weekday, and weekend estimates—with smartphone addiction scores among Saudi adults. Methods: This cross-sectional, web-based study recruited adults aged 18–65 years residing in Saudi Arabia through social media platforms. After excluding participants with missing anthropometric data, implausible body mass index (BMI) values, or total SB >24 h/day, 1037 participants were included (mean age 28.9 ± 11.5 years; 52.9% female). SB was assessed using the Arabic Sedentary Behavior Questionnaire and categorized into mentally active (e.g., desk work, reading, computer use) and mentally passive (e.g., television viewing, sitting while listening to music) domains. Smartphone addiction risk was measured using the Smartphone Addiction Scale (SAS). Multiple linear regression analyses were conducted to examine associations. Results: Participants reported 9.7 ± 4.6 h/day of total SB, including 5.3 ± 3.3 h/day mentally active SB and 4.4 ± 2.5 h/day mentally passive SB. High-risk smartphone addiction was prevalent (66.2%). In multiple linear regression models, mentally passive SB was strongly and positively associated with higher smartphone addiction risk in crude and adjusted analyses, including weekday and weekend estimates, whereas mentally active SB showed no significant associations. Adults with excessive total SB (≥8 h/day) had higher smartphone addiction scores than those with < 8 h/day (107.5 ± 32.0 vs. 94.6 ± 31.2; p < 0.001). Conclusions: These findings indicate that mentally passive SB, rather than mentally active SB, is consistently linked to elevated smartphone addiction risk, with stronger associations observed across both weekdays and weekends.