Smartphone Addiction and Health Indicators in Portuguese University Students: The Moderating Role of Physical Activity

Background/Objectives: Smartphone addiction has emerged as an important public health concern among university students and has been linked to risky movement patterns, such as physical inactivity, prolonged sitting time, and poor sleep outcomes. The purpose of this study was to examine the relationships between smartphone addiction, sleep quality, sleep duration, sitting time, and physical activity among Portuguese higher education students, as well as to see if physical activity moderates the relationship between smartphone addiction and health-related behaviors. Methods: A cross-sectional correlational study included 147 Portuguese higher education students (70.1% male; mean age = 20.11 ± 1.94 years). Data were gathered by an online questionnaire that included the Smartphone Addiction Scale-Short Version (SAS-SV), the International Physical Activity Questionnaire-Short Form (IPAQ-SF), and the Pittsburgh Sleep Quality Index (PSQI-PT). Descriptive statistics, Spearman correlations, Mann–Whitney U tests, and hierarchical multiple linear regression analysis were run. Results: The prevalence of smartphone addiction was 22.4%. Smartphone addiction was positively associated with sitting time (r = 0.226, p = 0.007) and negatively associated with physical activity (r = −0.169, p = 0.047). The link between smartphone addiction and sleep quality (ΔR2 = 0.035, p = 0.028) and sleep duration (ΔR2 = 0.039, p = 0.017) was associated with a weaker relationship with physical activity. However, neither interaction survived Bonferroni correction for multiple comparisons (adjusted α = 0.017). Conclusions: Smartphone addiction is associated with increased sedentary behavior and decreased physical activity levels. The exploratory moderation pattern observed suggests a potential role of physical activity in the relationship between smartphone addiction and sleep indicators, pending replication in larger and more heterogeneous samples.