You’ve probably heard this before, but listen up: Exercise is incredibly valuable, not only for general health, but for its mood-boosting effects, too. You don’t need to run a marathon to reap the benefits of exercise. In a recent study, researchers had depressed patients pedal a stationary bike, measuring their subjective symptoms and cortisol (stress hormone) levels before and afterwards. They found that after just 15 minutes of exercise, both the patients’ symptoms of depression and cortisol levels were significantly reduced.