A newly published study suggests that exercising an hour or more per week could lower the incidence of depression. The study followed 33,000 adults in Norway for 11 years, and found that an hour or more of weekly exercise was associated with 12% fewer cases of developing depression. But note that it didn't prevent anxiety.
Interestingly, the researchers found that "regular leisure-time exercise of any intensity" had these positive effects - it doesn't have to be aerobic or incredibly strenuous exercise. Exercise is associated with a number of biological changes that could have an impact on mental health. From Science Daily:
A landmark study led by the Black Dog Institute has revealed that regular exercise of any intensity can prevent future depression -- and just one hour can help. Published in the American Journal of Psychiatry, the results show even small amounts of exercise can protect against depression, with mental health benefits seen regardless of age or gender.
In the largest and most extensive study of its kind, the analysis involved 33,908 Norwegian adults who had their levels of exercise and symptoms of depression and anxiety monitored over 11 years. The international research team found that 12 percent of cases of depression could have been prevented if participants undertook just one hour of physical activity each week.
A healthy cohort of participants was asked at baseline to report the frequency of exercise they participated in and at what intensity: without becoming breathless or sweating, becoming breathless and sweating, or exhausting themselves. At follow-up stage, they completed a self-report questionnaire (the Hospital Anxiety and Depression Scale) to indicate any emerging anxiety or depression.
Results showed that people who reported doing no exercise at all at baseline had a 44% increased chance of developing depression compared to those who were exercising one to two hours a week. However, these benefits did not carry through to protecting against anxiety, with no association identified between level and intensity of exercise and the chances of developing the disorder. [Original article.]