Exercise has been dubbed "nature's antidepressant" by doctors for years, and now a new study confirms the notion.

The finding follows a four-month look at the impact that running had on anxiety and depression when compared to a common antidepressant.

SSRIs (selective serotonin reuptake inhibitors) work by boosting levels of serotonin, a neurotransmitter that's a key player when it c...