In England in 2006 more than 1 in 5 children measured in reception year (age 5), as a result of the National Childhood Measurement Programme were either overweight or obese (Dinsdale and Rutter, 2008). In year 6 (age 11), nearly 1 in 3 children measured were overweight or obese. As the population evolves and advances our reliance on convenience foods, technology, and transport has resulted in a negative energy balance. Children are consuming too many high fat/sugar energy dense food and drinks, and are living sedentary lifestyles (Butland et al., 2007). All this has resulted in the average weight of children in England increasing, and concern arises from the health consequences of childhood obesity.
Consequences of childhood obesity
A recent systematic review showed obese children suffer psychological ill-health as a result of their morbidity, such as low confidence and self-esteem (Wardle and Cooke, 2005). Research also highlights significant long-term cardiovascular risk factors for childhood obesity. Obese children are at an increased risk of type II diabetes, left ventricular mass abnormalities, hypertension and blood lipid disorders (Barlow, 2007). Asthma, orthopaedic conditions, and fatty liver disease have also been shown to be associated with childhood obesity (Dietz, 1998). Due to the long-term consequences of childhood obesity it is now high on the priority list of most Western governments to tackle (Who, 2000).
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All school children in reception year (aged 5) and year 6 (aged 11) are now routinely measured for height and weight as part of the National Child Measurement Programme (Dinsdale and Rutter, 2008). This is so trends in overweight can me recorded and monitored, and also for establishing accurate baseline figures for obesity prevalence. Trends can then be compared to other populations and the impact of any interventions can be analysed to see if it has any effect on the proportion of overweight children within the population. Another reason for monitoring trends is so comparison between different populations can be made, and then worldwide trends in overweight can be monitored. However, this has led to a number of challenges.
Measuring childhood obesity
Measuring childhood obesity does present science and public health with a range of methodological problems. Body mass index (weight/heightÂ²) is widely used in adult populations. Cut off points have been classified for adults 18.5 kg/mÂ² to 24.9 kg/mÂ² is considered healthy, 25 kg/mÂ² to 29.9 kg/mÂ² overweight, and above 30 kg/mÂ² obese.
A BMI of above 30 kg/mÂ² is recognised internationally as a definition of adult obesity; however children are still growing so BMI needs to be adjusted for age and sex (Cole et al., 2000). Establishing international trends for childhood obesity has been challenging due to the wide variations in definitions of childhood obesity worldwide. BMI cut off points for obesity in adults are established from survey data obtained from cross-sectional surveys in the UK, reference data for BMI is based on National Diet and Nutrition Surveys. Centile cut off points are identified at the point, where health risk of obesity rises steeply.
Childhood obesity has been thought of as cosmetic problem and cut off points when health risk increases is difficult to establish with any precision as children have less obesity related disease than adults (Cole et al., 2000). During puberty adolescents will double their weight and increase in height on average by 20%, as boys and girls also grow very differently this means establishing acceptable cut off points has been a challenge. Another challenge is hoe different countries define childhood obesity. For example, the French define a child obese above the 97th Centile; in the UK a child over the 95th Centile is defined as obese. Cole , et al (2000) proposed cut off points for childhood obesity are supported by the International Obesity Task Force and are based on international survey data, however much international debate is still ongoing on defining childhood obesity for international comparison worldwide (Who, 2000).
Research within the scientific literature refers to childhood obesity as an "international epidemic" with 2.3 to 3.3 fold increases in the USA over 25 years. In the UK 2.0 fold to 2.8 fold increases, Brazil, 3.6 fold increase, Ghana 3.8 fold increase, Australia 3.4 fold increase in boys, 4.6 fold increase in girls (Who, 2000).
Obesity is the result of the increase in energy intake and decrease in energy expenditure overtime for the vast majority of children (Barlow, 2007). Preventing and treating obesity therefore involves trying to change behaviour and lifestyle, and aims to ensure people eat less and become more active. This is referred to as the common sense cure for childhood obesity by some researchers (Ebbeling et al., 2002). Interventions aimed at tackling and preventing childhood obesity focus on childhood periods of risk for adult obesity highlighted from scientific evidence (Dietz and Gortmaker, 2001).
Critical periods in the development of childhood obesity
Gestation and early infancy
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Research shows three critical periods exist for the development of obesity in childhood (Dietz, 1994). These periods are during gestation and early infancy, between the ages of 5 to 7, referred to as adiposity rebound, and during indolence. Obesity that occurs in these periods increases the risk of adult obesity and adverse health outcomes (Dietz, 1994). Studies showing that infants that were exposed to famine prenatally or during early life suggest prenatal and perinatal over or under nutrition influences the development of fatness in later life.
Other large epidemiological studies involving 300,000 19 year-old men have confirmed this association (Ravelli et al., 1976). During in utero nutritional exposure it is hypothesised that appetite regulation and adipocyte numbers may be entrained within this time period. Exposure to under nutrition in the late in utero period may reduce adipocyte replication in the third trimester of pregnancy, impairing food intake regulation and increase the risk of obesity in later life (Dietz, 1994). In the third trimester, early under nutrition or over nutrition may protect or promote obesity in later life as it may influence adipose tissue cellularity (Dietz, 1994). Research has also highlighted low birth weight as a potential risk factor for obesity later in life (Butte, 2009).
Adiposity rebound is another critical time period where studies have shown an increased risk of development of obesity. In the first year in life BMI increases, then decreases until around the age of 5 when BMI is seen to increase again for a second time (Siervogel et al., 1991). This second time period is referred to as the adiposity rebound and research shows it may have a significant effect on body fatness in adolescence. The hypothesis is that children who experience adiposity rebound early, at age 5 have significantly larger sub scapular skin fold thickness measurements than children who experience this second rebound period later, aged 6 to 7 (Siervogel et al., 1991).
Research shows children who develop obesity during the adolescence period of development are at increased risk of morbidity in later life (Must et al., 1992). A long-term 55 year follow up study showed mortality increased for overweight adolescence. Morbidity for both adolescence boys and girls significantly increased for those in the obese category for BMI. One hypothesis that has been explored for adolescent developmental obesity is body fat distribution occurring during the adolescent period. As adolescents mature body fat appears to be deposited centrally and peripheral fat decreases during this time period (Mueller, 1982).
Treatment and Prevention Interventions
The intellectual and psychological immaturity of children is an obstacle to treating and preventing childhood obesity. Children are less well developed than adults therefore this has helped shape the type of interventions targeted at children. Most interventions have focused on family and school based interventions. Other interventions have looked at pharmacological and surgical treatments (Oude Luttikhuis et al., 2009).
Observational studies have shown a link between breast feeding and childhood obesity. Children who are breast fed compared to formula fed were less likely to be obese (Armstrong and Reilly, 2002). A recent meta-analysis of 9 studies with more than 69,000 participants showed a risk reduction for breast feeding with an odd's ratio of 0.78, 95% CI (0.71, 0.85) (Harder et al., 2005). However the authors report one limitation of this study was the exclusion of certain studies that may have resulted in publication bias. Including more studies in the analysis may have reduced the protective effective seen for breastfeeding.
A number of robust systematic reviews have taken place to examine the evidence for childhood obesity interventions. One point to highlight despite is the quality of the reviews, are the limitations of published studies included, and this suggests interventions have had little impact on this global epidemic.
The Cochrane library has published several robust reviews to investigate the effectiveness of treatment programmes for childhood obesity. A review in 2003 looked at interventions for treating childhood obesity (Summerbell et al., 2003). This reviewed identified randomised controlled trials of lifestyle interventions for treating childhood obesity. 18 randomised trials were included with 975 participants, the majority of studies included were hospital based specialist clinics aimed at treating the condition. The author's highlighted included studies were of insufficient statistical power to detect a true effect of the intervention, and as trials had differing outcomes it was not possible to conduct a meta-analysis of included trials. Most trials included motivated groups of patients making it difficult to generalise the results to the wider population who may not be as motivated as this group. This review concluded that there was insufficient evidence to support anyone treatment over another due to the sample sizes of included trials and their lack of generalise ability (Summerbell et al., 2003).
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A systematic review in 2005 looked at approaches to obesity prevention in children and was one of the strongest reviews published so far in terms of the robust methodology used (Summerbell et al., 2005). The authors had strict inclusion criteria and located 22 studies included in the review. 10 long term studies were included, 2 physical activity, 2 diets, and 6 combined diet and physical activity showed there was no treatment effect. Only one study included showed a significant effect on BMI of girls. Only one study within the review showed a significant effect for skin fold thickness changes, but not when looking at BMI change. The results led the authors to conclude that interventions to date did not significantly influence weight of children.
Research has highlighted a number of support structures required for effective management of childhood obesity. Parental support, family structure and function, and home environment are all important factors when tackling childhood obesity (Doak et al., 2006). Recent studies including these approaches have shown a more positive effect on children than earlier reviews. A recent meta-analysis of family based treatment programmes for childhood obesity included 44 treatment and/or control groups, 16 studies met the criteria for meta-analysis finding a large and significant mean effect size of - 0.89 for family interventions (95% CI = - 1.06 to - 0.73) for BMI standard deviation score (Young et al., 2007).
This review is further supported by a recent Cochrane update review which looked at childhood obesity treatment interventions using combined approaches involving increasing physical activity levels of participants, behavioural and psychological approaches aimed at changing diet (Oude Luttikhuis et al., 2009). When investigating treatment interventions for childhood obesity, this meta-analysis showed a much smaller effect size - 0.06 (95% CI = - 0.12 to -0.01) for BMI standard deviation score. This robust review included 64 RCT's with 5230 participants, 12 studies looked at physical activity and sedentary behaviour, 6 looked at diet, and 36 looked at behaviour change treatment approaches including cognitive behavioural therapy and solution focused therapy. 10 interventions included drug treatment and no surgical interventions were considered. Again this review concluded there was insufficient evidence to support one treatment option over another. Combined treatment involving behaviour and lifestyle interventions did produce small statistically significant reductions in overweight children and adolescents (Oude Luttikhuis et al., 2009).
What components of an intervention are effective is unclear within multi-component interventions within the literature. Limited high quality evidence exists for prevention and treatment based family interventions and further research is needed to gain greater understanding of which components are most important to include in order for family based interventions to be effective (Katz et al., 2008). Research also highlights the is little evidence of the cost effectiveness of interventions targeted at young children to prevent obesity (Bond et al., 2010). A review published in the Health Technology Assessment Journal reviewed 595 childhood obesity papers and reported that none of them were robust enough to be included in a cost effectives systematic review (Bond et al., 2010). There are gaps in evaluating the cost-effectiveness of these interventions and this is something that needs to be addressed by future studies.
School based interventions
School based interventions for childhood obesity have focused on delivering nutritional based educational messages, interventions to decrease television viewing, promote physical activity, modification of school meals and improving nutritional standards (Gonzalez-Suarez et al., 2009). Systematic reviews of the literature however report they have had little impact on childhood obesity (Jaime and Lock, 2009). The small number of published studies and concerns over different methodologies used makes robust evidenced based reviews of the literature difficult. Research also shows varying effects between girls and boys. For example, quantative analysis suggests social learning approaches may be more beneficial amongst girls, with boys showing benefit from environmental physical activity approaches (Kropski et al., 2008). This review identified 14 studies for inclusion; however the authors highlight 10 of these identified papers offered only weak grade two quality evidence.
In a population based evidence review of childhood obesity interventions targeting the school setting that focused on behaviour change approaches found only modest changes in behaviour (Sharma, 2006). This review highlights television viewing as being the most modifiable behaviour observed. When reviewing systematic reviews of the evidence for treatment and prevention programmes it is difficult to form a judgement. Although systematic reviews show only a small effect size, some randomised trials included in studies have shown significant positive effects (Sacher et al., 2010b).
Published randomised controlled trials aimed at treating obesity have shown positive benefits on BMI. Of 94 children who participated in a community based programme between 2004 and 2005 in the UK found 71% of children at 6 months had shown a decrease in BMI standard deviation scores. At 6 months mean change in BMI - 0.07, SD 0.16, p < 0.01) (Rudolf et al., 2006). A study assessing the feasibility of the MEND programme showed slightly better mean change BMI standards deviation scores at 6 months. Mean BMI was - 0.8, SD 1.2, p < 0.05, significant changes in waist circumference were also observed mean waist circumference - 3.4, SD 2.0, p < 0.05 (Sacher et al., 2005). Although these studies have shown significant improvements in BMI both studies have been feasibility studies therefore sample sizes have been small, hence why some meta-analysis have failed to find an effect when pooling these studies together.
As these interventions evolve and develop more robust trials are just beginning to take place. Standardisation of intervention protocols should take place for more consistent delivery across different settings. There needs to be an increase in the use of multiple health markers to gain a clear picture of how the different components of an intervention influence how effective it is. A randomised controlled trial of the MEND programme found significant improvements in BMI z-scores at 6 months ( -0.24, p < 0.01) and ( 0.23, p < 0.01), for improvements in cardiovascular fitness when compared to controls (Sacher et al., 2010a). Even these larger trials have scientific limitations; firstly, blinding of participants is not always possible reducing validity and reliability. High attrition rates are often seen in interventions; a third limitation is also the short follow up, (baseline to 12 months). This also limits conclusions for the long-term effects of these trials.
A prospective cohort study has shown significant benefits for young children, 185 overweight children attending a weight loss camp for a mean stay period of 29 days, lost on average 6.0 kg and reduced BMI by 2.4 units. BMI standard deviation scores of 0.28 were also observed when compared to controls (Gately et al., 2005). This multi-component program highlights children can achieve weight loss, however results cannot be generalised to the wider population. Such weight loss camps are also extremely expensive and beyond the budgets of most NHS Primary Care Trusts.
Nature of the evidence
From a public health perspective the increasing severity and prevalence of childhood obesity demands increased funding for research into new dietary, physical activity and behaviour approaches for both prevention and treatment interventions.
Systematic reviews and meta-analysis have failed to give a clear picture of how successful prevention and intervention strategies have been at tackling childhood obesity. Participants are often recruited through existing specialist clinics treating obesity or through advertisements and this can further affect the results as participants who respond may well be very motivated to succeed leading to bias results. Public Health practitioners are still unsure of the most effective services to commission to impact on childhood obesity.
Randomised control trials in a variety of settings in clusters throughout England to increase the quantity and quality of available evidence so more accurate assessments of effectiveness can be made. These should use current best practice examples of interventions such as those developed by MEND, Carnegie weight management and the WATCH IT Programmes.
Increase the number of following trials with large sample sizes and multiple trials sites in England. Studies should have a minimum of 80% power to detect an affect in each trial to ensure each study is robust. Multi-centred trials in the following areas should help increase the knowledge and move the science forward and aid understanding within this field:
Family based prevention and treatment interventions, randomised controlled trials - community, hospital based, GP based.
School based prevention and treatment interventions, cluster randomised controlled trials.
Physical activity RCT alone, cluster randomised controlled trials.
Diet alone, cluster randomised controlled trials.
Psychological approaches, CBT, Solution focused, cluster randomised controlled trials.
Combined physical activity, diet, and psychological approaches, cluster randomised controlled trials.
Economic cost-effective analysis of trials so real life costs can be assessed for best practice within the NHS.
Systematic review of all trials to establish the most effective approaches to use.
Although though overall effect of interventions to prevent and treat childhood obesity is a little disappointing, there are many positive robust studies that demonstrate there is still much to learn. Continued investment is required on a much larger scale to give scientists and the NHS enough information to commission robust interventions in a number of different settings to obtain the robust data required to act. Until further evidenced based long-term studies exist, current interventions will fail to treat and prevent childhood obesity on the scale required to reduce the future health and economic burden of this disease.