Relationship Between Perceived Stress and Anxiety in High School Senior Students: The Mediating Role of Social Support and the Moderating Influence of Lifestyle

(1) Background: The purpose of this study was to investigate the associations between perceived stress and anxiety in high school senior students, taking into account the possible influence from lifestyle (physical activity, nicotine dependence, and alcohol use) and social support. (2) Methods: A representative sample of high school senior students (N = 405; mean age: 18.2 ± 0.4), reflecting the overall geographic distribution of Lithuania's student population, was investigated using anonymous questionnaires on perceived stress (Perceived Stress Scale, PSS-10), anxiety (Generalized Anxiety Disorder Scale, GAD-7), perceived social support (Multidimensional Scale of Perceived Social Support, MSPSS), lifestyle (Fagerström Test for Nicotine Dependence), alcohol use (Alcohol Use Disorders Identification Test, AUDIT), and physical activity (International Physical Activity Questionnaire, IPAQ). Hierarchical multiple regression analysis was employed, investigating mediating and moderating effects. (3) Results: The direct effect of perceived stress on anxiety was significant (<i>B</i> = 0.364; SE = 0.0486; 95% CI [0.268, 0.459]; <i>p</i> < 0.001). Furthermore, the analysis revealed a significant indirect effect via social support (<i>B</i> = 0.387; SE = 0.0525; 95% CI [0.284, 0.490]), indicating that a portion of the relationship between perceived stress and anxiety was mediated by social support. Physical inactivity, alcohol use, and nicotine dependence served as moderators. Our findings confirmed that all three moderators showed significant interaction effects, with standardized β = -0.124, <i>p</i> = 0.002, for physical inactivity, β = 0.073, <i>p</i> = 0.016, for alcohol dependence, and β = 0.119, <i>p</i> = 0.001, for nicotine dependence, in the relationship between perceived stress and anxiety among high school senior students. (4) Conclusions: These findings have practical insights for educators who implement physical activity and alcohol and nicotine usage programs for high school senior students to help reduce their stress and anxiety.