The prospective relation between physical activity and Diagnostic and Statistical Manual of Mental Disorders-defined major depression in middle childhood is unknown, as is the stability of depression. We therefore aimed to (1) determine whether there are reciprocal relations between moderate-to-vigorous physical activity (MVPA) and sedentary behavior, on one hand, and Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition defined symptoms of major depressive disorder, on the other and (2) assess the extent of stability in depressive symptoms from age 6 to 10 years.
A community sample of children living in Trondheim, Norway, comprising a total of 795 6-year-old children was followed up at 8 (n = 699) and 10 (n = 702) years of age. Physical activity was recorded by accelerometry and symptoms of major depression were measured through semistructured clinical interviews of parents and children. Bidirectional relationships between MVPA, sedentary activity, and symptoms of depression were analyzed through autoregressive cross-lagged models, and adjusted for symptoms of comorbid psychiatric disorders and BMI.
At both age 6 and 8 years, higher MVPA predicted fewer symptoms of major depressive disorders 2 years later. Sedentary behavior did not predict depression, and depression predicted neither MVPA nor sedentary activity. The number of symptoms of major depression declined from ages 6 to 8 years and evidenced modest continuity.
MVPA predicts fewer symptoms of major depression in middle childhood, and increasing MVPA may serve as a complementary method to prevent and treat childhood depression.
Comments
RE: Does exercise protect against depressive symptoms?
To the editor
Zahl et al report that children aged 6 to 8 who engage in moderate-to-vigorous physical activity (MVPA) manifest fewer symptoms of major depression. In their discussion, the authors mention various ways—physiological, psychological, and social—in which exercise may protect from mood disorders and propose the testing of programs to increase MVPA at a population level.
The authors fail to consider an alternative explanation for the association they observe: perhaps the propensity to engage in MVPA is linked genetically to mood resilience. That is what De Moor et al (1) found in an eleven-year longitudinal study of 5952 adult twins and their families: common genetic factors predisposing to both increased likelihood of exercising and decreased incidence of symptoms of anxiety and depression.
In this sample, an identical twin who exercised more did not display fewer mood symptoms than his or her co-twin who exercised less, nor did increases in exercise participation predict the observation of fewer symptoms.
These findings correspond to a common-sense view that people less prone to depression may be livelier, likelier to join group activities, and so on. Exercise has clear medical benefits, but studies suggesting that it protects from depressive symptoms tend to ignore this potential confound, the possibility that any observed association may arise from a shared innate or temperamental propensity to engage in MVPA and enjoy mood resilience.
Reference
De Moor, M. H., Boomsma, D. I., et al., “Testing Causality in the Association Between Regular Exercise and Symptoms of Anxiety and Depression,” Arch Gen Psychiatry 65 (2008): 897–905