Overview of included studies
Of the 153 RCTs, 39 (25%) engaged children aged 0-5 years, 85 (56%) children aged 6 to 12 years, and 29 (19%) children and young people aged 13-18 years. Most studies were conducted in North America (n=77, 50%) and Europe (n=45, 29%), with relatively few in Australasia (n=15, 10%), Asia (n=7, 5%), South America (n=6, 4%),and the Middle East and North Africa (n=3, 2%). The majority were carried out in high‐income countries (n=139; 91%), with 13 (8%) in upper‐middle‐income countries, and one (1%) in a lower‐middle‐income country (based on the World Bank classifications). Most (n=91, 59%) were delivered in a school setting (primary, middle and secondary schools); 23 (15%) were delivered in the community; 6 (4%) were delivered in a health care setting; 22 (14%) in childcare which included nurseries, child-care centres, kindergartens and pre-schools; and 11 (7%) were delivered in home. The types of intervention in the Cochrane Review (16) were divided into three, those that primarily delivered dietary interventions (n=21, 14%); those in which the intervention was predominantly physical activity (n=39, 21%); and the majority, in which both diet and physical activity were delivered (n=93, 61%). These data were drawn from the Cochrane Review (16).
Distribution of interventions against the WDoH
When looking at the distribution of the 242 intervention efforts from the 153 studies (Figure 1, Panel A), 57.9% (n=140) of all efforts targeted ILF, 37.1% (n=90) at LWC, 3.7% (n=9) at SCF, and 1.2% (n=3) at WC. None of the interventions sought to change determinants at the BF level. In Figure 1 (Panel A), the intervention efforts are contrasted against the 226 perceived causes of obesity from Public Health England Action Mapping Tool (9). Over 60% of causes were coded as LWC (n=74, 32.7%) or WC (n=62, 27.4%), and the remaining 40% were coded as BF (n=22, 9.7%), ILF (n=37, 16.4%) or SCF (n=31, 13.7%) – illustrating a notable imbalance between intervention efforts and the perceived causes of obesity.
Table 2 demonstrates how the interventions focused on multiple WDoH levels. Of those interventions which focused on one level of the WDoH only (n=73), most sought to influence ILF (n=61). Studies that targeted two levels of the WDoH were likely to focus on ILF and LWC combined (n=70/74 studies). Seven studies targeted three levels (often ILF, LWC, and SCF), and only one study (26) addressed four levels of the WDoH (ILF, SCF, LWC, and WC respectively). Of note, 140 of the 153 studies (91.5%) had a focus on the ILF level.
Table 2: Foci of interventions across multiple levels of the WDoH
Number of WDoH levels interventions coded at
|
Level of the WDoH model
|
Number of studies (%)
|
BF
|
ILF
|
SCF
|
LWC
|
WC
|
One
|
-
|
✓
|
-
|
-
|
-
|
61 (39.8%)
|
|
-
|
-
|
-
|
✓
|
-
|
11 (7.2%)
|
|
-
|
-
|
-
|
-
|
✓
|
1 (0.6%)
|
Two
|
-
|
✓
|
-
|
✓
|
-
|
70 (45.8%)
|
|
-
|
-
|
✓
|
✓
|
-
|
1 (0.6%)
|
|
-
|
✓
|
✓
|
-
|
-
|
1 (0.6%)
|
Three
|
-
|
✓
|
✓
|
✓
|
-
|
6 (3.9%)
|
|
-
|
✓
|
-
|
✓
|
✓
|
1 (0.6%)
|
Four
|
-
|
✓
|
✓
|
✓
|
✓
|
1 (0.6%)
|
Footnote: Interventions were able to be coded at more than one level of the WDoH model. Table 2 demonstrates the foci of the interventions included within the 153 studies. For example, 61 studies solely focused on changing ILF, whereas 70 studies targeted ILF and LWC combined. These data are based upon the coding completed by two members of the research team (JN and THMM).
|
Specific foci of intervention efforts within the WDoH
In the secondary level of analysis, this study sought to understand the focus of intervention efforts within each of the WDoH levels. Forty-two codes (i.e. intervention focal points) were agreed upon (i.e. codes), of which the 153 studies were coded against on 411 occasions (Online Supplement I). Studies ranged from one intervention focus (n=39 studies) through to nine (n=1 study), with a mode of two foci per study.
Fourteen codes were generated for interventions targeting ILF. Thirteen of these had education at their core, however seven codes were specifically related to education targeted at parents, and five targeted children. For parents and children alike, the main focus of education was to improve multiple health behaviours (i.e. diet, physical activity, and sedentary behaviour combined) (cited in 55 studies which provided education for parents and in 75 studies for children). Beyond this, educational content varied greatly between studies, from a focus on parenting skills (n=5 studies), to screen time (n=4 studies), to infant feeding (n=4 studies). The one code at the ILF level which was not education-based was the provision of additional after-school physical activity (n=27 studies).
Very few interventions that aimed to influence determinants at the SCF level (n=9 studies), with substantial variation between interventions as where efforts were placed. Three interventions sought to influence the social norms around physical activity, with two also targeting social norms around health more broadly. Other efforts included the organisation of social events, community involvement in the intervention delivery, and peer champion training or peer involvement. The level of information provided within study descriptions that pointed towards SCF, in contrast to other levels, was often limited.
However, for interventions which intervened at the LWC level, consistent patterns emerged within the data, despite 19 codes being created (see Online Supplement I). The provision of teacher training was the most frequently observed code (n=39 studies), which often meant that interventions aimed to upskill staff so that they can deliver intervention educational material to children. Further structural changes were also noted within the curriculum; 31 interventions provided additional physical activity during school hours and 30 interventions embedded further content about positive health behaviours. Other commonly noted codes included modifications to the food- (n=10 studies) and physical activity- (n=8 studies) environments, as well as the provision of alternative food and drink options largely in school-based settings (n=20 studies).
Three interventions targeted efforts at the WC level. Only two codes were generated for efforts at this level. Two interventions employed state and district wide policies, both of which aimed to influence school food environments. One intervention worked with the Ministry for Public Education to encourage the school level adoption of the obesity prevention programme. This study, by Shamah Levy et al. (27), was considered to be the most comprehensive intervention included within the analysis, and targeted the ILF, LWC and WC levels.
Changes in intervention focus over time
The pattern of intervention efforts remained consistent over time (see Panel B, Figure 1). Of the 20 studies published before 2005, 57.1% of intervention effort was placed on ILF and 35.7% on LWC. Between 2006 and 2010, when a further 45 studies were published, these new interventions continued to focus their efforts on changing ILF (57.4%) and LWC (33.8%). With a further 88 studies published after 2010, the focus remained consistent; 57% of intervention efforts focused on changing ILF and 38.3% on LWC. Interventions frequently focused on, and were coded at, more than one level of the WDoH.
Changes in intervention focus between age groups
Panel C (Figure 1) highlights that there are no discernible trends between the focus of interventions efforts regarding age groups (<5 years, 6-12 years, and 13-18 years). One point to note is that slightly more emphasis was placed on changing SCF in interventions developed for 13-18 year olds, often by aiming to change social norms within the cohort (n=3 of the 5 studies targeting SCF). As aforementioned, interventions could be coded at multiple levels.