Exercise and other forms of physical activity elicit a wide range of beneficial health effects. Findings from a large study in Sweden suggest that physical activity reduces the risk of depression.

The observational study involved more than 395,000 people who were followed over a period of 21 years. The study participants were either skiers who partook in Vasaloppet, an annual long-distance cross-country ski race held annually in Sweden (physically active), or non-skiers (physically inactive). Vasaloppet skiers typically exercise a minimum of four hours weekly and have a high level of physical fitness.

The findings indicated that physical activity was associated with a 50 percent lower risk of developing depression during a 10-year period compared to physical inactivity. Adjustments for age, sex, and education did not alter the results.

Some have suggested that the association between higher level of physical activity and lower risk of depression might be an artifact of reverse causation. For example, people with depression – especially those whose condition is undiagnosed – might be less likely to engage in physical activity. However, Mendelian randomization studies and data from molecular, genetic, and interventional trials suggests that the relationship is indeed causal.

Check out our in-depth video covering exercise and depression, including data from randomized controlled trials, Mendelian randomization trials, mechanistic studies, and even ideal exercise parameters.

An easy take-home message: Aerobic exercise at 70 to 80 percent of maximum heart rate for 40 minutes or more may be critical for boosting brain-derived neurotrophic factor (BDNF) – a growth factor that controls and promotes the growth of new neurons.

• Link to full study.