A systematic review of the effectiveness of individual, community and societal level interventions at reducing socioeconomic inequalities in obesity amongst children

Interventions can be characterised by their level of action and their approach to tackling inequalities. Whitehead [25] describes four levels of interventions to tackle inequalities: strengthening individuals (person based strategies to improve the health of disadvantaged individuals), strengthening communities (improving the health of disadvantaged communities and local areas by building social cohesion and mutual support - via collective activities), improving living and school environments (reducing exposure to health-damaging material and psychosocial environments across the whole population), and promoting healthy macro policy (improving the macro-economic, cultural and environmental context that influence the standard of living achieved by the whole population). According to Graham and Kelly [14], these interventions are underpinned by one of three different approaches to health inequality: disadvantage (improving the absolute position of the most disadvantaged individuals and groups), gap (reducing the relative gap between the best and worst off groups), or gradient (reducing the entire social gradient). Interventions are thus either targeted (directed at those who are disadvantaged) or universal (interventions that influence the entire social gradient).

The aim of this review was to systematically examine the effectiveness of interventions (individual, community and societal) operating via different approaches (targeted or universal) in reducing socio-economic inequalities in obesity-related outcomes amongst children. A companion paper examines interventions for reducing socioeconomic inequalities in obesity amongst adults [26].

The following electronic databases were searched from their respective start dates up to the 11^th October 2012: MEDLINE, EMBASE, CINAHL, PsycINFO, Social Science Citation Index, ASSIA, IBSS, Sociological Abstracts and the NHS Economic Evaluation Database (see Additional file 1 for the full search strategies). We did not exclude papers on the basis of language, country or publication date. The electronic database searches were supplemented with website and grey literature searches.

Our review examined interventions at the individual, community and societal (environment and macro policy) level that might reduce inequalities in obesity-related outcomes amongst children aged 0-18 years. Interventions that aimed to prevent obesity, treat obesity, or improve obesity-related behaviours (diet and/or physical activity) were considered relevant, so long as they provided relevant information and analysis on both socioeconomic status and obesity-related outcomes. We defined individual level interventions as those that included individualised/one-to-one health promotion, education, advice, counselling or subsidy and were conducted in a health care or research setting, or in participant’s homes. Community level interventions were defined as group-based health promotion, education, advice, counselling or subsidy only interventions, or interventions conducted in a community setting (for example a school, community centre, sports centre and shop). We have classified the group-based educational interventions as community, rather than individual interventions, using ‘the intent’ of the intervention as an aid to classification[29]. Although we acknowledge that an element of the intent of these types of interventions is to strengthen individuals (increase ‘agency’) by targeting behaviour change, we believe that the main intent is to target the condition (group setting, peer support, peer pressure, etc) in which behaviour occurs. We do acknowledge that it is a grey area for these types of studies. Societal level studies were split into two sub-groups: Societal-environment level interventions as those that included a change in environment or access to environment; and Societal-policy level interventions as macro-level policies such as taxation, advertising restriction or subsidies. Interventions were also classified in terms of whether they took a gradient approach and included participants of all socio-economic status (SES) (“universal” interventions) or a targeted approach i.e. aimed at low SES participants only (“targeted” interventions). Measures and proxy measures of SES were parental income, parental education, parental occupation, area level or school level disadvantage (for example number of pupils receiving free or reduced school meals). We did not include ethnicity (or faith or culture) as a measure of SES. Interventions that involved drugs or surgery, and laboratory-based studies, were excluded from the review.

Our review considered prevention and treatment interventions that might reduce socioeconomic inequalities in the prevalence of obesity-related outcomes (i.e. effective interventions targeted at low SES children, or universal interventions that work equally or more effectively in low SES children compared with high SES children).

Our full review [28] included randomised controlled trials (RCTs) and non-randomised controlled trials (classified as experimental studies) that included either a non-treatment control group or standard treatment group, and prospective and retrospective cohort studies, with or without control/standard treatment groups, and prospective repeat cross-sectional studies with or without control/standard treatment groups (classified as observational studies). Only studies with duration of at least 12 weeks (combination of intervention and follow up) were included. The justification for using a 12 week cut-off was a pragmatic one, in that most existing interventions and initiative, particularly those which are school based, are of a shorter duration, for example over one school term. Given that the aim of our review was to provide useful information for policy makers and commissioners of services, who will be mindful of costs (driven, in part, by duration of the intervention), we did not want to exclude such interventions from our review; the same criteria (and justification) was used in a Cochrane review on interventions to prevent obesity in children [30]. That said, we appreciate that longer term (e.g. one year) changes in obesity-related outcomes would provide a more confident assessment of the effectiveness of such interventions. For the purpose of this article only the best evidence available for each intervention level is reported and, therefore, only RCTs and non-randomised controlled trials (experimental studies) were included.

Studies were included if they reported an obesity-related outcome (e.g. weight and height; body mass index; waist measurement/waist to hip proportion; percentage body fat; skin fold thickness; ponderal index) and if they examined differential effects with regard to socio-economic status, or were targeted specifically at disadvantaged groups or were conducted in deprived areas.

The initial screening of titles and abstracts was conducted by one reviewer with a random 10% of the sample checked by a second reviewer. Data extraction was conducted by one reviewer using established data extraction forms and independently checked by a second reviewer. The methodological quality of the included studies was appraised independently by two reviewers using the Cochrane Public Health Review Group recommended Effective Public Health Practice Project Quality Assessment Tool for Quantitative Studies [31]. This tool includes, amongst other things, an examination of sampling strategy, response and follow-up rates, intervention integrity, statistical analyses and assessment of adjustment for confounders. We used the quality appraisal criteria for descriptive purposes and to highlight variations between studies. Any discrepancies were resolved through discussion between the authors and, if consensus was not reached, with the project lead.

Our full review [28] used broad study inclusion criteria and conducted a wide search in order to capture the entire evidence base on the effects of interventions to reduce inequalities in obesity-related outcomes amongst children. This resulted in a very large evidence base that was much larger than anticipated. To make sense of it for policy and practice, this article focuses only on a narrative synthesis of the ‘best available’ international evidence for each intervention type. Best available evidence was defined in terms of both study design and study quality by each intervention type so that only those studies that provided the highest quality for each intervention type are synthesised in this paper.

Three of the ‘best evidence’ studies included children of pre-school age (0-5 years), all of the studies included children of primary school age (6-12 years) and one study included children of secondary school age (13-18 years). Three of the studies were conducted in the USA and one in Australia. Study details are summarised in Table 1 with intervention effects sizes reported in Additional file 2: Tables S1-S2 and where data are available. None of the studies in this section were based in a school setting; study settings included healthcare centres, participant’s homes, and community sites. The studies included in this section have been grouped by a) those which aimed to prevent further weight gain in children at high risk of obesity, or treat obesity, b) those which aimed to prevent obesity, or improve obesity-related behaviours (diet and/or physical activity).

Half of the ‘best evidence’ community level studies (n = 7) were conducted in the USA with four from South American countries (two from Brazil, and one each from Chile and the Republic of Peru), four from Europe (two from the Netherlands and one each from Finland and France) and one each from Australia and Israel. The majority of studies (n = 13) included children of primary school age (6-12 years), three studies included children of preschool age (0-5 years) and one included adolescents (13-18 years). All of the studies included boys and girls (usually an approximately 50/50 mix), with the exception of three studies that included girls only. Study details are summarised in Table 2 with intervention effects sizes reported in Additional file 2: Tables S3 and S4 where data are available. The studies included in this section have been grouped, firstly, as school-based interventions or interventions in other settings, and then subdivided (where studies were available) into a) those which aimed to prevent obesity, or improve obesity-related behaviours (diet and/or physical activity) or b) those which aimed to prevent further weight gain in children at high risk of obesity, or treat obesity.

The ‘best available’ evidence for the environmental interventions comes from one strong quality experimental study that followed a universal approach and compared intervention effects of low SES children (using parent education as a proxy measure) versus higher SES children [53, 54]. The study examined a multi-faceted school based obesity prevention intervention that was conducted in pre-schools in Switzerland. The intervention included changes to the school’s environment to encourage physical activity (fixed and mobile equipment such as climbing walls, hammocks, balls and stilts) along with the provision of healthy snacks, nutrition education and exercise sessions. This reasonably sized study (n = 625) found some beneficial intervention effects overall after 9½ months in terms of body fat and waist circumference, but not BMI or prevalence of overweight [54]. Sub-group analysis revealed no significant differences in intervention effects between children with low education parents and those with parents of medium/high education; however, there was a trend towards more beneficial effects in the higher SES children [53].

One strong quality experimental study [55] examined the effects of a three year community capacity-building intervention amongst 1,807 children of all SES aged 4-12 years in Australia (universal approach). The intervention was designed by a number of key organisations to build the community’s capacity to create its own solutions to promoting healthy eating, physical activity and healthy weight, and the delivered universally in all intervention schools. After three years, children in the intervention schools showed significantly lower increases in waist circumference (adjusted difference between comparison and intervention = -3.14; p = 0.01) and BMI z-score (adjusted difference = -0.11; p = 0.04) compared with the children in the control schools. There was no association between SES measures and intervention effects in the intervention schools; however, lower SES was associated with a greater gain in body fat and waist circumference in the control schools. Therefore, the intervention halted the widening of inequalities in obesity that would normally naturally occur over time.

At an individual level, the results from the ‘best available’ evidence (n = 4) identified by our review suggests that mentor-based health promotion interventions may be effective in reducing obesity prevalence in low SES children as there were particular benefits to those low income children who were already overweight or obese (one year); and that a screen time reduction intervention was more beneficial for low SES children after two years.

The ‘best available’ evidence of the effectiveness of community level interventions (n = 17) was mixed, as whilst some studies identified effective interventions both in the short- and long-term (amongst children aged 6-12), others did not. Therefore, this review has found that there is some – but not conclusive evidence – that school based nutrition and physical activity education and exercise sessions and school-delivered screen time reduction interventions were effective in the longer term (over six months) in reducing obesity-related outcomes amongst school aged children with no differential effects by SES. In the shorter-term (up to six months), family based education and behavioural weight loss programmes, and exercise based weight loss programmes targeted at low SES school aged children were effective in reducing obesity-related outcomes. There was some evidence of effectiveness of school based nutrition and physical activity education and exercise sessions amongst pre-school children in the longer-term (one year). There was no evidence of effectiveness from the one ‘best evidence’ study amongst adolescents.

Our review identified only one strong quality experimental study of more upstream environmental interventions and no studies of the effects of macro-level policy interventions on obesity-related outcomes amongst children. The multi-faceted school based obesity prevention intervention was found to be effective amongst pre-school children in the longer term (over six months) but with slightly more beneficial effects to those of higher SES. Finally, a multi-level community capacity-building intervention was effective in preventing a widening of inequalities in obesity amongst children aged 4-12 over the long term (up to three years).

The majority of the ‘best available’ evidence was from interventions conducted in the USA or South America. In most cases interventions appeared to be equally effective – or ineffective - for boys and girls – although some studies did not distinguish their results by gender. Most of the studies were of interventions targeted at low SES children/areas and often of ‘treatment’ interventions for those already overweight or obese. In terms of ‘where’ interventions appeared to be effective, the ‘best available’ evidence was dominated by school-delivered interventions and this suggested that school-based interventions targeted at low SES children could have some beneficial effects in reducing inequalities – although the evidence was by no means conclusive. This is in line with the ‘Whole School Approach’ to tackling childhood obesity. The findings of effectiveness are therefore very much limited to the effectiveness of school-based interventions, for low-income, primary school-aged children (6-12 years), particularly in the USA.

We did try to further unpick the various programme components that were used in the studies included in this review, to identify in detail why some interventions had a positive impact on inequalities in obesity-related outcomes, and others did not, particularly for interventions which appeared similar but had different effects. We did not systematically look for separate process evaluations as this was beyond the scope of the review, although we acknowledge that would have been helpful. From the information provided to us in the research papers, there were no consistent themes which shone through beyond those mentioned above. Importantly, there was no evidence that the studies included in this review increased inequalities in obesity-related outcomes. Whilst we wait for results of ongoing relevant interventions, and assuming interventions which tackle obesity-related outcomes do not increase inequalities, we suggest that interested stakeholders refer to a Cochrane review by Waters [30] which suggest the following to be promising policies and strategies:

The direction of research and evaluation in this field must move into how to implement effectively to scale, sustain the impacts over time, and ensure equitable outcomes of interventions to manage childhood obesity and reduce associated inequalities. We recommend larger, longer term studies, powered to detect the small changes that are likely to be found, with assessments of equity impacts, to enable translation of research findings into effective public health approaches for managing childhood obesity.

The majority of interventions that we included in this part of our review were aimed at preventing weight gain, although a number of ‘treatment’ interventions were also included. These ‘treatment’ interventions are more likely to show positive effects than prevention ones. The targeted approach also has limitations as even when interventions are effective amongst low income groups they are only able to reduce the health inequalities gap, they have little effect on the wider social gradient. Most studies were school based and aimed at primary school aged children (6-12 years). There were also very few studies of societal level interventions that might be expected to have more of an impact on the gradient in obesity [27]. We also found no studies that assessed the cost-effectiveness of interventions and meta-analysis was not appropriate given their heterogeneity.

Our results show that there is a clear need for more experimental studies of the effectiveness and cost-effectiveness of interventions to reduce inequalities in childhood obesity, particularly in adolescents and in terms of macro-level interventions that potentially address the entire gradient. There has been a real missed opportunity to evaluate the effects of such ‘real world’ interventions, and future interventions (such as Fulfilling Lives: A Better Start) should include such analysis. It is worth highlighting the ongoing EPHE (EPODE for the Promotion of Health Equity) evaluation study which aims to provide useful information about the impact of the EPODE intervention on socioeconomic inequalities across Europe; ‘Ensemble Prévenons l’Obésité Des Enfants’ (EPODE, Together Let’s Prevent Childhood Obesity) is a large-scale, coordinated, capacity-building approach for communities to implement effective and sustainable strategies to prevent childhood obesity [56].

Our review has found only limited effectiveness of interventions with the potential to reduce SES inequalities in obesity. The body of evidence in this review provides some support for the hypothesis that obesity treatment interventions in children can be effective and that for interventions targeted at low SES children they have reduced obesity-related outcomes; for universal interventions they have reduced the SES gradient in obesity-related outcomes. Interventions need to be developed so that they can be embedded into ongoing practice and operating systems, rather than implementing interventions that are resource intensive and cannot be maintained long-term. This review also highlights that although we may now have a good sense of the range of interventions feasible for use in reducing the risk of childhood obesity, we lack the knowledge of which specific intervention components are most effective to ensure that the equity gradients reduced. Being able to answer this question is of critical importance to decision makers.

This review was very extensive as an extremely thorough search was conducted of the international literature with a very broad inclusion and exclusion criteria that has ensured that the entire relevant evidence base was captured. This has enabled us to focus in this paper on just the best available (experimental) evidence. Quality is additionally high as double screening was applied and both data extraction and quality appraisal were independently checked. However, the review is still subject to some methodological limitations as for example the quality assessment tool, although described as a tool for public health interventions, seemed to favour those that followed a more clinical model. We particularly found the blinding question unhelpful as it mostly resulted in moderate scores. The definitions for level of intervention that were used, adapted from the health inequalities literature, meant that most studies were categorised as community level interventions. Other ways of categorising studies (such as by whether primary prevention programmes are more/less/even effective in decreasing or haltering inequalities compared to selective prevention programmes), or by examining the theoretical underpinning of interventions (such as those that are based on Social Cognitive Theory, Planned Behaviour or theories of Environment–Behaviour Relationships) could also have been used. One final limitation is our exclusion of studies that examined ethnic inequalities that may have reduced the USA literature where ethnicity is often used as a proxy for SES.