By Dr. Geoffrey Modest
And, perhaps the last blog on exercise, at least for now…
A Norwegian study assessed the relationship between physical activity, sedentary lifestyle, and DSM-IV defined major depressive disorder (MDD) in kids aged 6 to 10 years old (see DOI: 10.1542/peds.2016-1711).
- Community sample of 6-year-old children (n=795) in Trondheim, Norway were followed-up at 8 and 10 years of age.
- Physical activity was recorded by accelerometry – wearing an accelerometer for 7 consecutive days, 24 hours a day, and only removing when bathing or showering; they assessed the time period of 6 AM till midnight and excluded periods of time where there were greater than 20 minutes of 0 counts (suggesting they were not wearing the unit); sedentary activity was <100 counts per minute; and moderate-to-vigorous physical activity, MVPA, was >2296 counts per minute). Major depression was assessed through semistructured clinical interviews of parents and children using the Preschool Age Psychiatric Assessment (PAPA), with a summed score creating the DSM-IV defined MDD; and the Child and Adolescent Psychiatric Assessment (CAPA) was used as well for children 8 and 10 years old.
- DSM-IV defined MDD decreased from age 6 to 8 but then increase from age 8 to 10. (the prevalence of MDD was around 0.5% in all of the age groups)
- Minutes of MVPA did not change from age 6 to 8 but decreased from age 8 to 10
- Sedentary activity increased from age 6 to 8 and increased further from age 8 to 10
- The symptoms of MDD and sedentary activity were modestly stable over this time. MVPA was more stable.
- Cross-sectional findings
- The symptoms of MDD were negatively correlated with MVPA at age 8 and 10, but were unrelated to sedentary activity.
- At both ages of 6 and 8, higher levels of MVPA predicted fewer symptoms of MDD 2 years later, with a reduction of 0.2 symptoms of depression per daily hour spent in MVPA
- There was no difference between males and females.
- MVPA predicted reduced numbers of MDD symptoms from age 6 to 8, but depression did not predict later MVPA (i.e. it seems to be unidirectional). And there were no effects of sedentary activity on depression or vice versa
- Some studies have found that physical activity may reduce the likelihood of the symptoms of major depressive disorder in adolescents and adults (see Craft LL. Prim Care Companion J Clin Psychiatry 2004; 6: 104, which includes meta-analyses showing exercise’s therapeutic benefit, on the order of cognitive therapy).It has been unclear whether this was related to the physical activity or the lack of sedentary behavior (these 2 are not perfectly correlated, and, for example, children may do periods of intense activity but have a lot of sedentary behavior time). This Norwegian study assessed these factors prospectively in younger children, finding that MVPA mattered but sedentary behavior time did not
- One particular strength of this study is that they did look at symptoms of depression over time, since these often wax and wane. Also the study allows us to looks at the bi-directionality of the relationship between physical activity and depression, finding that the results were unidirectional from MVPA to MDD. Another advantage of the study over others is that they used a formal assessment of depression as well as a formal assessment of exercise.
- The effect size of MVPA on MDD symptoms was small, but still on the order of magnitude of those of psychosocial intervention programs in children. And medications do not always work (and probably have more adverse effects than exercise…). So, exercise may well be an important therapeutic approach to treating depression in kids (i.e., not just preventative, as suggested in this study, and should probably be formally evaluated).
- Some postulates as to why physical activity might decrease depressive symptoms include: these activities might distract children from thinking about negative events; physical activity in children also may bolster their self-esteem; and physically active children are more socially integrated into peer groups.
- The mechanism by which physical activity might have helped include: higher availability of neurotransmitters which are depleted in people with depression and which may have antidepressant effects if augmented (e.g. serotonin, dopamine and norepinephrine); the potentially positive role for exercise-induced endorphins (see above cited article by Craft); also, there is evidence of increased cerebral blood flow and cognitive function with exercise. Other studies have shown that children taking exams in school do better when they are more physically active prior to taking those exams.
- One quite concerning social evolution is that many schools have cut out physical education/activity in order to cram in more academic subjects. Unfortunately, this could not just lead to decrease school performance, but also reinforce future patterns of inadequate physical activity. It is concerning in this study that exercise decreased and sedentary time increased from ages 8 to 10.
So, MVPA did predict fewer future MDD symptoms in children, and such symptoms were relatively stable from ages 6 to 10. Sedentary activity however did not affect the risk of future symptoms of depression, and depression does not seem to influence the likelihood of MVPA or sedentary behavior. Their conclusion was that increasing MVPA at a population level may prevent depressive symptoms or MDD. And I think it makes sense for us in primary care to strongly encourage physical activity and advocate for more exercise in schools, and that exercise be considered an integral part of the curriculum, emphasized and promoted by the school system. And that there be more neighborhood-friendly and safe exercise venues, etc. Per the prior blogs and the myriad articles on the benefits of exercise, this is not just to prevent depression…