Article Text

Childhood obesity: should primary school children be routinely screened? A systematic review and discussion of the evidence
  1. Marie Westwood1,
  2. Debra Fayter1,
  3. Suzanne Hartley2,
  4. Amber Rithalia1,
  5. Gary Butler3,
  6. Paul Glasziou4,
  7. Martin Bland5,
  8. John Nixon1,
  9. Lisa Stirk1,
  10. Mary Rudolf6
  1. 1Centre for Reviews and Dissemination, University of York, York, UK
  2. 2Clinical Trials Research Unit, University of Leeds, Leeds, UK
  3. 3Institute of Health Sciences, University of Reading, Reading, UK
  4. 4Department for Primary Health Care, University of Oxford, Oxford, UK
  5. 5Department of Health Sciences, University of York, York, UK
  6. 6Department of Community Paediatrics, Leeds Primary Care Trust and University of Leeds, Leeds, UK
  1. Correspondence to:
    Dr Marie Westwood
    Centre for Reviews and Dissemination, University of York, York YO10 5DD, UK; mew3{at}york.ac.uk

Abstract

Background: Population monitoring has been introduced in UK primary schools in an effort to track the growing obesity epidemic. It has been argued that parents should be informed of their child’s results, but is there evidence that moving from monitoring to screening would be effective? We describe what is known about the effectiveness of monitoring and screening for overweight and obesity in primary school children and highlight areas where evidence is lacking and research should be prioritised.

Design: Systematic review with discussion of evidence gaps and future research.

Data sources: Published and unpublished studies (any language) from electronic databases (inception to July 2005), clinical experts, Primary Care Trusts and Strategic Health Authorities, and reference lists of retrieved studies.

Review methods: We included any study that evaluated measures of overweight and obesity as part of a population-level assessment and excluded studies whose primary outcome measure was prevalence.

Results: There were no trials assessing the effectiveness of monitoring or screening for overweight and obesity. Studies focussed on the diagnostic accuracy of measurements. Information on the attitudes of children, parents and health professionals to monitoring was extremely sparse.

Conclusions: Our review found a lack of data on the potential impact of population monitoring or screening for obesity and more research is indicated. Identification of effective weight reduction strategies for children and clarification of the role of preventative measures are priorities. It is difficult to see how screening to identify individual children can be justified without effective interventions.

  • BMI, body mass index
  • IOTF, International Obesity Taskforce
  • NSC, National Screening Committee
  • PCT, Primary Care Trust
  • obesity
  • overweight
  • monitoring
  • screening
  • BMI

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In an effort to accurately map the growing epidemic of childhood obesity (the proportion of overweight or obese children between the ages of 2 and 10 rose from 22.7% in 1995 to 27.7% in 20031), the UK government has recently introduced population monitoring in primary schools. A nationally co-ordinated population monitoring programme has benefits in terms of facilitating the gathering of epidemiological data. It is also a potentially useful tool for assessing the impact of health promotion programmes such as the School Fruit and Vegetable Scheme and the National Healthy Schools Programme upon prevalence of overweight and obesity (although it cannot establish a causal relationship). Current evidence suggests that preventative strategies for children can change behaviour, increasing levels of physical activity and encouraging a healthier diet, but little is known of their long-term efficacy in reducing the prevalence of obesity.2

The UK House of Commons Health Committee report on obesity expressed particular concerns about the long-term health consequences of obesity in children,3 and a government target has been set to halt its increase by 2010.4 The report recommended that “results should be sent home in confidence to parents, together with, where appropriate, advice on lifestyle, follow-up, and referral to more specialised services”. This approach remains controversial. Pressure to move from population monitoring to identifying overweight and obese individuals is driven by the notion that highlighting the problem and intervening early could improve long-term health outcomes.5 There is currently little evidence that weight reduction interventions are effective,6 and without this evidence any move towards identifying individual children appears difficult to justify. An additional difficulty arises as the limited evidence about effective interventions is derived from studies in motivated, often self-referred populations, and caution must be exercised in extrapolating the results to a screening scenario. Current Department of Health guidance for Primary Care Trusts (PCTs)7 on measuring body mass index (BMI) in primary school children emphasises population monitoring and discourages the use of measurement to identify individual children with weight problems until such time as evidence becomes available to support the effectiveness of doing so. It is worth noting that little is known about the potential harms of monitoring overweight and obesity, either in the context of population monitoring or screening to identify individual children.

We were commissioned by the Health Technology Assessment Programme to produce a systematic review of the clinical and cost-effectiveness of growth monitoring in children of primary school age to identify growth-related conditions. In consideration of the rise in childhood obesity within this age range and the national debate currently being conducted in the media, we included monitoring for overweight and obesity in our assessment. This article reports our findings in relation to the clinical effectiveness of monitoring for overweight and obesity, and describes those areas where evidence is lacking and where research should be prioritised.

METHODS

The systematic review was undertaken in accordance with published guidelines.8 Two reviewers screened studies for relevance independently, and full texts of studies deemed potentially relevant were ordered and assessed for inclusion by one reviewer and checked by a second. Data extraction and quality assessment were carried out using standard forms, developed and piloted a priori; data were extracted by one reviewer and checked by a second. At all stages, disagreements were resolved by consensus or consultation with a third reviewer.

All study designs (except case reports) were included. For relevance to the UK population, studies had to include children aged between 4 and 11 years in Western Europe, North America or Australia/New Zealand (excluding studies of aboriginal populations). Studies had to measure indices of overweight and obesity as part of a population-level assessment of children’s health. Accepted outcome measures were:

  • the effects on management and outcome (including specialist referrals),

  • indices of diagnostic accuracy (sensitivity and specificity) in comparison with direct measures of body fat,

  • any measure of the attitudes to monitoring (including surrogate measures such as uptake rate),

  • any measure of the human resource implications of introducing monitoring.

We did not include studies whose primary outcome measure was population prevalence, as this is already well established.

The full search strategy is available from the authors on request. Databases searched are listed in supplemental table 1 (available from http://adc.bmj.com/supplemental); no language restrictions were applied. Unpublished information on current practice and audit data were sought by directly contacting all PCT lead personnel in child health/community paediatrics and all Strategic Health Authority lead personnel in child health services in England and Wales.

Table 1

Overview of all diagnostic accuracy studies identified

The methodological quality of diagnostic accuracy studies was assessed using the QUADAS tool9,10 with appropriate review-specific modifications.

Data are summarised in a narrative, and we present a summary of the available evidence against the National Screening Committee (NSC) criteria, along with a discussion of directions for future research.

RESULTS

Figure 1 shows the flow of studies through the review process (including studies of growth monitoring to identify stature-related conditions). Despite searching a wide range of sources using a search strategy optimised for sensitivity (over 30 000 records were retrieved and screened), we identified only a small number of relevant studies. It is significant that no study addressed, either directly or indirectly, the effectiveness of either population-level monitoring or screening to identify and treat individual children.

Figure 1

 Flow chart of studies through the review process (including studies of growth monitoring to identify stature-related conditions). This study focuses on the areas covered by the studies reporting the diagnostic performance of indices of overweight and obesity, providing information on attitudes to monitoring for overweight and obesity and providing information on the human resource implications of introducing monitoring.

Diagnostic accuracy studies

Eleven studies provided data on the diagnostic accuracy of measures used to identify overweight and obesity in comparison with direct measurement of body fat.11–21 Studies varied widely in their sample size, country of origin, and the age or ages at which children were measured. An overview of the studies is presented in table 1. Reasoning that any monitoring programme would need to access simple measuring techniques, we have focussed on those studies13–16,21 that assessed BMI, weight or skinfold measures in comparison with the accepted reference standards for determining percentage body fat (x ray densitometry, hydrostatic weighing or isotope dilution).

BMI was the predominant measure of overweight and obesity evaluated. Thresholds used to define overweight and obesity varied between studies and were derived either internally from the study population, from national or other published data, or from International Obesity Taskforce (IOTF) definitions. Full details of the methods of measurement assessed and the reference standards used are presented in table 2. A number of the studies appeared to have been conducted with the aim of establishing the optimum simple measurement method for determining overweight and obesity; that is, they compared a number of different measurements or thresholds with one or more thresholds for directly measured body fat. Heterogeneity between the studies precludes any generalisations about what might be the optimum simple measure of overweight and obesity; the results of individual studies are presented in table 2.

Table 2

 Results of the five diagnostic accuracy studies that assessed BMI, weight or skinfold measures in comparison with an accepted reference standard for determining percentage body fat

None of the five studies clearly met all of the 12 QUADAS criteria. The quality assessment was limited by the poor reporting of a number of studies. The index measures and reference standards were generally well reported, with all but one study giving sufficient details to allow replication.13,15,16,21 The results of methodological quality assessment are presented in supplemental table 2 (available from http://adc.bmj.com/supplemental).

Human resource implications of monitoring

One study included information relevant to the human resource requirements of monitoring.22 This study considered general health examinations conducted at or around the time of school entry. It compared the ability of physicians with that of trained volunteers (teachers) and public health nurses to detect abnormalities in height, weight, vision, hearing, blood pressure and dental caries. No significant differences were observed.

Attitudes to monitoring

One study assessed attitudes to monitoring overweight and obesity.23 The study aimed to gather baseline BMI data in order to identify a low cost method of detecting obesity that would be acceptable to schools. A total of 252 children aged 9–10 years participated in the one-off measurement. There were three (1.2%) refusals to participate; parental consent was obtained on an opt-out basis. The study was conducted in the context of a lesson on measurement and was designed to minimise negative impacts. The results of a questionnaire, sent to teachers and school nurses, suggested general satisfaction. It should be noted, however, that this was a small study, using an approach that had been conceived with a view to minimising negative impacts. Further, no attempt to elicit the views of the participating children was reported.

Assessment against National Screening Committee criteria

An assessment of monitoring to identify childhood overweight and obesity is presented against the NSC criteria in table 3. Deficiencies and uncertainties in the evidence mean that monitoring which aims to identify and treat individuals does not currently meet the majority of the criteria.

Table 3

 Assessment of monitoring to identify childhood overweight and obesity against the National Screening Committee (NSC) criteria

DISCUSSION

Statement of principal findings

It is clear that monitoring to detect and treat individual overweight and obese children does not currently meet the NSC criteria. Although childhood obesity is an important public health issue with increasing prevalence and important consequences (co-morbidities of obesity in childhood include type 2 diabetes, hypertension, dyslipidaemia, emotional and behavioural problems, asthma and sleep apnoea),24–26 uncertainties concerning its definition and appropriate treatment mean that most of the screening criteria have not been met. There remains, however, a fundamental question as to whether or not the NSC criteria are a valid tool for assessing general health monitoring programmes such as monitoring overweight and obesity or monitoring children’s growth. Abnormalities of stature or weight are not, in themselves, disease states and therefore, arguably, monitoring children’s health with respect to these parameters should not be considered a screening exercise. Nonetheless, a rigorous approach to clarifying harms and benefits is required.

Despite its failure to meet the NSC criteria, monitoring levels of childhood overweight and obesity in the population may have inherent informative value. The importance of consistent data gathering and the availability of local data to inform planning and resource targeting are recognised in Department of Health guidance to PCTs,7 although it should be noted that population data cannot provide evidence of the effectiveness of resource targeting. If data gathered in monitoring programmes could be linked to individuals, it might also prove useful in clarifying the risk relationship between childhood BMI and long-term morbidity and mortality into adulthood. However, the value of moving from population monitoring to screening to identify and treat individual children remains, at best, questionable; it is fundamentally dependent on benefits outweighing harms. The effectiveness of treatment is currently doubtful and the potential harms of either monitoring or screening are poorly researched. In the light of this, current models of self-referral appear the best basis for attempts to treat obesity and should continue. The use of the population monitoring programme to identify individual children and provide information to parents and carers, as recommended in the UK House of Commons Heath Committee report on obesity,3 would represent a move towards screening that would be difficult to justify on the basis of current evidence.

Strengths and weaknesses of the study

Our review provides the first systematic evaluation of the available data on monitoring for overweight and obesity in children. The strengths of the study lie in its use of rigorous systematic review methodology to address an important aspect of child health. The review included a comprehensive search strategy and extensive attempts to obtain unpublished studies, but was unable to provide definitive information on the value of monitoring childhood overweight and obesity for a number of reasons. Firstly, and perhaps most significantly, no controlled studies were found evaluating monitoring versus no monitoring for the detection and treatment of overweight and obesity. Secondly, although 11 studies providing data on the diagnostic accuracy of measurement techniques were identified, these studies had a number of methodological limitations. More importantly, these studies are more informative on the limitations of BMI (and other measures) as indicators of overweight and obesity in one-off comparisons with direct measures of body fat than on the more important question of whether monitoring for overweight and obesity using BMI (or any alternative surrogate measure of body fat) can provide a useful predictor of long-term morbidity and mortality, or is a useful exercise when compared with no monitoring. The limitations of BMI as a one-off screening tool are clear but are not of direct relevance to the utility of long-term monitoring.

Only very limited data were available on the human resource implications of monitoring growth and/or overweight and obesity, although a number of important issues concerning training, costs and referral were identified.

The potential harms which may arise from labelling children as overweight or obese, or from raised personal and peer group awareness generated by population monitoring without identification, are an important and understudied area. We identified just one study that specifically assessed attitudes to monitoring and this was conducted in a context expressly designed to minimise negative impact.23

Meaning of the study: implications for policy makers

The relative benefits and harms of monitoring have not been determined and the effectiveness of current treatments is doubtful. Given these and other uncertainties, a move from population monitoring towards screening to identify and treat individual overweight and obese children could not currently be justified under the NSC criteria. A consistent approach to population level monitoring and the collection of local data is likely to be useful in providing epidemiological data and guiding planning and resource allocation for preventative and general health promotion strategies, but cannot be used to reliably determine the effectiveness of such strategies. Policy makers also need to consider the extent to which it is appropriate to evaluate general health monitoring programmes against the NSC criteria.

Current Department of Health guidance to PCTs7 focuses on population monitoring and discourages the giving out of BMI results to parents and carers or children. Involvement in healthy schools programmes is encouraged and it has been suggested that this may be a route for providing feedback to parents27; providing “whole school” information, on a regular basis, in the context of the healthy schools programme could increase awareness without moving from monitoring to screening and the identification of individual children. However, the potential harms of stigmatisation arising from raised peer group awareness remain a consideration.

Unanswered questions and future research

Funding for UK research into the relative benefits and harms of using monitoring to identify and treat overweight and obesity in childhood should be of a high priority before any move away from population monitoring and towards screening is considered. Particular emphasis should be given to randomised controlled trials to identify effective weight reduction strategies for children. Research should measure long-term outcomes (sustained weight loss, co-morbidities and mortality into adulthood). Evidence that an effective intervention can be offered is a prerequisite to the introduction of screening.

Preventative strategies are promising in terms of effectiveness2 and attractive to policy makers and the general public, but they are currently unproven and larger and longer-term trials are urgently needed. The generation of reliable, local prevalence data from population monitoring may help in targeting preventative strategies and evaluating their impact. The impact of effective prevention strategies on the need to use monitoring to identify and treat individual children should also be considered.

Current knowledge of the long-term medical consequences of childhood obesity is limited. Establishing long-term epidemiological studies is now a high priority. These should help elucidate which children are most at risk of obesity persisting into adulthood and consequent adverse outcomes. Such studies could utilise data from population monitoring programmes if these data were collected in a manner which could be linked to individuals. This would clarify the role of parameters such as BMI, which can be monitored in community settings, in determining those children most at risk.

What is already known on this topic

  • Childhood obesity is an important and growing health problem in the UK.

  • Obesity in children can have significant consequences for health and well-being in the short term and into adulthood.

  • The effectiveness of interventions to treat childhood obesity remains doubtful, to date. Preventative strategies can change behaviour and promote healthier lifestyles, but their long-term impact is unknown.

What this study adds

  • Funding for UK research into effective interventions to treat overweight and obese children is a high priority; it is difficult to justify measures to identify individual children without evidence of effective interventions.

  • Primary prevention offers a promising approach to tackling childhood obesity, but is currently unproven.

  • More large scale, well designed studies are urgently needed in this area. If effective treatments can be identified, effort should be focused upon methods of identifying overweight and obese children without stigmatisation and upon defining the appropriate target population.

CONCLUSIONS

Our review found a lack of data on the potential impact of monitoring for overweight and obesity in children; more research is indicated. Identification of effective weight reduction strategies for children and clarification of the role of preventative measures are priorities. Long-term studies of the predictors of obesity-related co-morbidities in adulthood are warranted. This would clarify the role of parameters such as BMI in determining those children most at risk.

REFERENCES

Supplementary materials

Footnotes

  • MEW takes responsibility for the work from inception to publication and managed the project. GB, with MEW, conceived and formulated the project grant application. DF led all aspects of the systematic review from protocol development to the writing of the final report, and SH and AR performed all aspects of the systematic review. LS devised and conducted the searches. GB reviewed the protocol and final report and provided expert advice on issues connected with children’s growth and growth-related conditions. MR reviewed the protocol and final report and provided expert advice on issues connected with childhood obesity. PG provided advice on issues connected with screening and reviewed the protocol and final report, and MB and JN reviewed the protocols and final report and provided general advice.

  • This project was funded by the NIHR Health Technology Assessment Programme (project number 04/09/02) and will be published in full in Health Technology Assessment. See the HTA Programme website for further project information (http://www.hta.nhsweb.nhs.uk/).

  • Competing interests: None.

  • Ethics approval: Not required.

    The views and opinions expressed herein are those of the authors and do not necessarily reflect those of the Department of Health.

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