Long-term effects of exercise at different intensity levels on depression: A randomized controlled trial

•Research into the long-term effects of exercise intensity on depression is scarce.•Light, moderate and vigorous exercise was compared to treatment as usual (TAU).•Light exercise led to lower depression severity than TAU at 12 month follow-up.•Light and vigorous exercise resulted in lower depression severity than moderate exercise.

Previous research has shown positive effects of exercise on depression but studies have mainly focused on the short-term effects; few have examined the long-term effect, especially with regard to differences in intensity. The aim of this study was to examine the long-term effects of prescribed exercise on depression, performed at three intensity levels. People aged 18-67 years with mild to moderate depression (Patient Health Questionnaire-9 score of ≥ 10) participated in a single-blind, parallel randomized control trial lasting 12 weeks (Sweden 2011-2013). Four arms were included: Treatment as usual (TAU, n = 310), light (n = 106), moderate (n = 105) and vigorous exercise (n = 99). Severity of depression was measured at baseline, post-treatment and 12-month follow-up using the Montgomery-Åsberg Depression Rating Scale (MADRS). Coefficients (β) and odds ratios were estimated using linear mixed models with time × group interactions. The results showed that at the 12 month follow-up the light exercise group had significantly lower depression severity scores than the TAU (− 1.9, 95% CI: − 3.7, − 0.04) and the moderate exercise group (− 2.94 95% CI: − 5.2, − 0.7). The vigorous exercise group had significantly lower scores than the moderate exercise group only (− 2.7, 95% CI: − 4.9, − 0.4). In conclusion, compared to usual care for depression, only light exercise resulted in significantly lower depression severity at 12-month follow-up. Both light and vigorous exercise was more effective than moderate exercise.Trial registration: The study was registered with the German Clinical Trial Register (DRKS study ID: DRKS00008745).