Researchers studying exercise and depression have published their findings in JAMA Pediatrics that physical activity is not a predictive marker for levels of depression in teenagers.
Dr Helen Stain, Senior Clinical Lecturer (Psychological Interventions), School of Medicine, Pharmacy and Health at Durham University, said:
“It is alarming that young people may think this study shows that exercise is not necessary or important for them. People often do exercise with others and we know that social support is protective for mental health.
“The study is a randomized controlled trial of the effect of physical activity on protecting adolescents from depression and the results showed no statistically significant effect.
“There are a number of concerns with the methods that may have led to such a finding and are important to highlight.
“The reason the study did not find that exercise can protect teenagers from depression could be due to the low rates of depression in the sample with only 17 of the 736 adolescents identified as having depression at the start and only 28 at the end of the study. It could also have been due to the assessment of physical activity and depressive symptoms not being done at the same time so that it is not possible to be sure that physical activity was the only influence on depression.
“Importantly, the study did not statistically control for, or measure the level of social contact associated with physical activity. The protective intervention that the researchers were seeking may be this combination of social contact with physical activity.
“It is important that the results of this study are not interpreted as physical activity being of no benefit for adolescents but rather that more research is needed.”
Two authors of the study Prof Ian Goodyer, Child and Adolescent Psychiatrist, University of Cambridge and Dr Umar Toseeb, Postdoctoral Research Associate in School of Psychological Science, University of Manchester, said:
“Dr Stain has somewhat misunderstood the purpose and design of this research. This was a prospective longitudinal repeat measures design not a randomised controlled trial. The objective was to reveal if there was a naturalistic association over time between physical activity and depressive symptoms in adolescents aged 14 years at first assessment and 17 years at follow-up. We chose this age period because these mid-adolescent years are associated with marked changes in neurodevelopment and consequential shifts in physical parameters including activity and cognition. We have already shown how normative changes in sleep and appetite can be misconstrued as signs of depression in adolescents1. The same may be true for physical activity when there are marked changes in the maturing adolescent independent of affective and cognitive development.
“The statistical analyses used are appropriate for a prospective repeat measures design. Adolescents do not appear to be very accurate in their self-reporting of physical activity2 and we reduced this potential source of error by utilizing state of the art objective physiological measures3 of activity not biased by self-reporting of exercise or sedentary behaviours. We did include clinical depression episodes to ensure the lack of association was not hiding a stronger signal between under-activity at 14 years and the emergence of clinical depression by 17 years. We agree with Dr. Stain that a larger sample of depressed patients might show an activity-mental symptom correlation and this does need to be investigated. Such a study would need to take the effects of normal changes in physical activity over adolescence into account 3 and consider that reduced exercise may be a consequence of clinical depression. Our results have no relevance as to whether a physical activity intervention in such patients would be of value. That remains to be established as Dr. Stain indicates. In addition our results cannot be construed as proposing no value for physical activity only that in the teenage years activity and mental state may not be interdependent upon each other.
“The environmental origins of individual differences in physical activity are of great interest and certainly deserve further study. Social context may be one of a range of psychosocial variables involved in adolescent physical activity and we agree with Dr. Stain that these may particularly important as mediators in a trial design. This remains to be established.
“We suggest the findings highlight further evidence for a fundamental distinction in understanding the maturation of metabolic and cognitive systems in the second decade of life when there is the highest incident risk for major affective disorders. The results support prior research that in the adolescent population at large individual differences in eating sleeping and physical activity are driven more by latent maturational mechanisms than mental illness mechanisms. This suggests strongly that the subtype of major depression used in adults, known as atypical depression and characterised in part by core symptoms of increased appetite or weight gain, sleepiness or excessive sleep and marked fatigue or weakness should be used with extreme caution in the adolescent age range.”
‘Exercise and Depressive Symptoms in Adolescents: A Longitudinal Cohort Study’ by Toseeb et al. published in JAMA Pediatrics on Monday 13th October.