Depression in adolescents
Existing research demonstrates that depression among adolescents is highly prevalent worldwide and that rates have increased significantly since the 1980s [Collishaw et al, 2010, Collishaw et al, 2015, Mojtabai et al, 2016]. The risk of depression rises sharply as children transition into adolescence, with prevalence estimates of depression reported to be between 4-11% in mid-to-late adolescence and up to 20% by late adolescence [Mojtabai et al, 2016, Thapar et al, 2012, Birmaher & Brent, 2007].
A significant noted trend is the rise in prevalence of depression among adolescent females compared to males, estimated at 2:1 [Collishaw et al, 2010, Collishaw et al, 2015, Mojtabai et al, 2016, Thapar et al, 2012, Rice et al, 2017, Neufeld et al, 2017, NHS England, 2016, DHSC & DoE, 2017, Parkin et al, 2017]. Also of relevance is that Lesbian, Gay, Bisexual and Transgender (LGBT) young people report experiencing depression and anxiety, suicidality and self-harm at considerably higher rates than heterosexual young people of a similar age [Lea et al, 2014, Guasp, 2017]. Research in the United Kingdom (UK) and other high-income countries suggests that depression is more prevalent amongst people from Black and Asian Minority Ethnic (BAME) backgrounds [Mooney et al, 2016, Williams et al, 2015].
Recent research suggests that adolescents who seek help do benefit from contact with mental health services. The ROOTS longitudinal cohort study conducted in the UK [Neufeld et al, 2017] found that contact with mental health services by 14 year olds with depression reduced the likelihood of depression by age 17 years. There are also concerns regarding the use of antidepressant drugs for adolescents younger than 18 years [Sharma et al, 2016] and there is also a lack of strong evidence regarding the effectiveness of psychological treatments, such as Cognitive Behavioural Therapy (CBT) and Interpersonal Psychotherapy (IPT) [Thapar et al, 2012]. This suggests the need for alternative approaches such as promoting changes in behaviour and health behaviours such as exercise.
Exercise, high intensity training, and depression
There are several mechanisms that have been proposed to explain the many ways by which physical activity may be beneficial in the management of depression [Lawlor & Hopker, 2001]. Some of these might be via social mechanisms; physical activity participation can provide a diversion from depressive thoughts, opportunities to learn new skills, and increased socialisation [Lowe et al, 2008]. In addition, there may be physiological mechanisms; physical activity is associated with promoting the release of endorphins and other neurotransmitters which can improve mood [Mandolesi et al, 2018]. Further, inflammation has been identified as a potential contributor to the development of depression [Miller et al, 2009], suggesting that anti-inflammatory strategies, such as regular physical exercise [Gleeson et al, 2011] may be effective at preventing and managing depressive symptoms. However, the optimal intensity of exercise required has not been established and this information is critical when determining prescription.
There remains considerable uncertainty about the extent to which exercise intensity is related to benefit for depression.
Exercise for adolescents with depression
There is growing evidence that exercise may be an effective intervention to reduce depressive symptoms in adults [Cooney et al, 2013, Josefsson et al, 2014, Schuch et al, 2016, Chekroud et al, 2018]. For adolescents with depression the evidence base is scarce and evidence quality is poor.
A Cochrane review in 2006 [Larun et al, 2006] and subsequent systematic reviews in 2013, 2016 and 2018 [Brown et al, 2013, Carter et al, 2016, Bailey et al, 2018], respectively) examined the effects of exercise interventions in reducing depression and anxiety in children and adolescents. However, the low quality of the studies reviewed, the small number of studies included, small sample sizes, and a diversity of participants, interventions and methods of measurement limit the ability to draw conclusions. A recent pragmatic small scale RCT [Carter et al, 2015] conducted in the UK reported no effect on depressive symptoms at post-intervention, but a significant effect at six months in favour of the intervention, suggesting a delayed response. The authors concluded that large, well reported and robust trials conducted with help-seeking young people in real-world treatment settings are required.