BACKGROUND:An inverse association between total leisure-time physical activity (LTPA) and depression has been previously documented in the scientific literature. Our objective was to prospectively assess the association of LTPA with the risk of depression, focusing on several dimensions of LTPA (intensity, duration and type). METHODS:The SUN (Seguimiento Universidad de Navarra) project is a prospective cohort study formed by Spanish university graduates. A total of 15,488 adults (40.2% men, mean age 37 ± 12 years) initially free of depression were assessed. A report of a validated medical diagnosis of depression or the habitual use of antidepressants (any of both) were considered as incident cases of depression. LTPA was estimated through previously validated self-reported questionnaires. Participants were classified following Physical Activity recommendations from the World Health Organization, and according to the intensity, duration and type of LTPA. Cox proportional hazards regression models were run, adjusted for demographic, lifestyle, and dietary factors, to estimate adjusted hazard ratios (HR) of depression and 95% confidence intervals (CI). RESULTS:During 163,059 person-years of follow-up we registered 870 incident cases of depression. Participants with higher total LTPA (METs-h/wk) and higher duration of LTPA (hours/wk) exhibited a lower risk of depression HR = 0.84 (95% CI: 0.72-0.99) and HR = 0.83 (0.70-0.99) respectively, whereas intensity of LTPA (MET) did not show any association with depression. CONCLUSION:Participants with higher LTPA had a lower risk of depression. The inverse association was stronger for total LPTA time than for its intensity. Higher duration of LTPA should be encouraged to prevent depression.