NYT: Exercise and Depression

Mental Health: Exercise Is Found Not to Affect Depression
By NICHOLAS BAKALAR

Many people are sure that exercise improves their mood, and studies have suggested that exercise is almost as effective as antidepressants in relieving symptoms of depression. But a new study has found that even though people who exercise are less likely to be depressed or anxious, it is probably not because they exercise.
Dutch researchers studied 5,952 twins from the Netherlands Twins Registry, as well as 1,357 additional siblings and 1,249 parents, all 18 to 50 years old. They recorded survey data about the frequency and duration of exercise and used well-validated scales to uncover symptoms of depression and anxiety. The study was published Monday in The Archives of General Psychiatry.
Studying twins allowed the researchers to distinguish between genetic and environmental effects, and they found that the association of exercise with reduced anxious and depressive symptoms could be explained genetically: people disinclined to exercise also tend to be depressed. One does not cause the other.
This does not mean that exercise is useless in alleviating depressive symptoms. “Exercise may still be beneficial for patients being treated for an anxiety or depressive disorder,” said Marleen H. M. de Moor, the lead author of the study and a doctoral student in psychology at VU University Amsterdam. “But we couldn’t find evidence for a causal effect in the population at large.”

For more details, see Testing Causality in the Association Between Regular Exercise and Symptoms of Anxiety and Depression