Is physical activity a protective factor for emotional wellbeing in young people?

Background

WHO(1) state that mental health problems are a worldwide public health concern and consequently, promotion of mental health is a key component of UK public health policy(2,3). Foresight(5) recently published a report which has drawn together evidence in this field and provides a framework for further developments.

Mental illness has a long-term impact on people and is a risk factor for mortality and morbidity(5), costing the UK economy £100 billion a year(6). In 2004, 10% of children and young people aged 5-16 years had a clinically diagnosed mental disorder, the majority of which were either emotional (anxiety or depression) or conduct disorders(7). However, many more young people are thought to suffer from poor emotional wellbeing. This was demonstrated in a report by UNICEF(8) in which the UK ranked bottom for children's wellbeing in comparison with North America and 18 European countries. A number of policies have been developed with a specific focus on the health and wellbeing of young people (9-11) and recently, NICE published guidance for promoting social and emotional wellbeing in primary(12) and secondary(13) schools. These key documents clearly demonstrate the need for a focus on improving the emotional wellbeing in young people in the UK.

Knowledge about factors that protect against mental health problems and improve emotional wellbeing in young people is required. There is some evidence of a positive although guarded association between physical activity and emotional health outcomes in adults(14,15), but young people are seldom studied. There are two relevant Cochrane reviews, the first by Larun et al(16) who examined the evidence for physical activity reducing or preventing common mental health disorders (anxiety and depression) amongst children and adolescents. They concluded that there was some evidence for a beneficial effect although the evidence was not robust enough, given the heterogeneity in the populations studied, to draw any conclusions. Ekeland et al(17), in a related Cochrane review, concluded that exercise had positive short-term effects on self-esteem in children and adolescents. However, neither review directly examined the association between physical activity and general emotional wellbeing. Similarly, some longitudinal studies have examined the relationship between depression and physical activity in adolescence(18-20) yet only two have explored the relationship between physical activity and emotional wellbeing(21,22). Predominately, the evidence is based on cross-sectional studies(23-26).

Clear conclusions about the association between physical activity and emotional wellbeing are difficult to make largely due to the use of different definitions and measures of physical activity and failure to investigate the dose-response relationship - the optimal amount and type of physical activity (incorporating information on the frequency, duration and intensity of such activity) to achieve emotional health benefits(27,28). Moreover, there have been a number of terms used to refer to emotional wellbeing (e.g. psychosocial health, mental health) and a range of different self-report questionnaires for measuring emotional wellbeing, which also makes it difficult to compare findings between studies. Furthermore, little is understood about the mechanisms that may underlie an association between physical activity and emotional wellbeing(22).

The proposed analysis will form part of an NIHR doctoral fellowship supervised by Professor Rona Campbell (co-supervised by Professor David Gunnell and Dr Ashley Cooper).

The research will analyse data already collected as part of ALSPAC to address the following aims:

* To determine whether physical activity is a protective factor for emotional wellbeing in young people

* To investigate the dose-response relationship between physical activity and emotional wellbeing in young people

* To determine whether emotional wellbeing is a barrier to physical activity in young people

Hypotheses will be tested through analysis of data from 2000 children in the ALSPAC cohort and 1000 children in the AHEAD cohort. Baseline physical activity was measured in the ALSPAC cohort at 12 years and then at follow-up age 14 then 16 years; AHEAD at 12 years then 15 years. Emotional wellbeing was measured at baseline in ALSPAC at 11 years and then at follow-up age 13 years; AHEAD at 12 years then 15 years.

Outcome data

The primary outcome is total difficulties score as measured by the SDQ (Strengths and Difficulties Questionnaire) http://www.sdqinfo.com/b1.html (29). This scale was selected as it is a valid and reliable instrument suitable for young people aged 11-16 and it can also be completed by parents or teachers (30). The 25 items in the SDQ comprise of 5 scales (emotional symptoms, conduct problems, hyperactivity/inattention, peer relationship problems, and pro-social behaviour) with 5 items in each. A 'total difficulties score' is calculated for the first four sub-scales (range 0-40). A high score (20+) on the total difficulties score can be used to identify those that may have mental health disorders. The 5 sub-scales will also be investigated independent of each other (each sub-scale ranges from 0-10). Child self-reported SDQ data collected from the AHEAD cohort and maternal and teacher reported data from the ALSPAC cohort will be analysed and also compared to explore the quality and content of the SDQ data from different informants.

Exposure data

Accelerometers are objective physical activity measurement devices which provide precision of measurement, as they overcome children's lack of ability to recall and quantify physical activity (31). The Actigraph accelerometer was selected for use with both the ALSPAC and AHEAD cohorts as it has been validated in both children and adolescents. Two main physical activity variables will be derived- total physical activity and time spent in moderate or vigorous physical activity (MVPA). Appropriate cut-points will be used to determine moderate and sedentary levels of activity.

Linear regression analysis (for continuous outcomes) and random effects logistic analysis (for dichotomous outcomes) will be used. Potential confounding factors will be controlled for e.g. age, gender, socio-economic markers and ethnicity in AHEAD and a number of additional confounders available from the ALSPAC data. Gender-specific effects will be formally tested.

In the AHEAD cohort (n=1000), an odds ratio of 1.36 can be detected with 80% power (at 5% significance). ALSPAC will have a minimum of 2000 participants in any analysis (due to a smaller number with physical activity data at 16 years compared to 12 and 14 years). If n=2000, an odds ratio of 1.24 can be detected with 90% power (at 5% significance).

The possibility of using the longitudinal nature of the data more fully can be explored by using repeated measures analyses. The role of e.g. social support as a potential mediator of this association (using number of close friends reported in the ALSPAC data, and peer nominations in the AHEAD data) could be investigated and the potential pathways using path analysis examined.