Higher prevalence of childhood overweight and obesity in association with gender and socioeconomic status in the Hunter region of New South Wales

ORIGINAL RESEARCH

Higher prevalence of childhood overweight andobesity in association with gender andsocioeconomic status in the Hunter region of NewSouth Wales

Rachel SUTHERLAND,1,2 Meghan FINCH,1,2 Michelle HARRISON1 and Clare COLLINS2

1Hunter New England Population Health, and 2School of Health Sciences, University of Newcastle, Newcastle,New South Wales, Australia

AbstractObjective: To determine the prevalence of overweight and obesity in primary school-aged children in the Hunterregion and examine associations with gender, age, socioeconomic status (SES) and geographical location.Design: Cross-sectional survey of a stratified sample of randomly selected government primary schools in theHunter region with SES defined by Socio-Economic Index For Areas index and geographical location based on schooleducation areas.Subjects: A total of 2224 out of 5206 (42.7%) primary school children from randomly selected government primaryschools representing year 1 to year 6 (x = 9.61 � 1.7).Setting: Sixteen government primary schools in the Hunter Region of New South Wales.Main outcome measures: Overweight and obesity were assessed using the international body mass index cutpoints, standardised for both age and gender as defined by Cole.Data analyses: Chi square (a = 0.05) was used to compare prevalence across categories of gender, age, SES orgeographical location.Results: Of the 2224 children who had their height and weight measured, 28.35% (n = 606) were either overweight(n = 415, 19.3%) or obese (n = 191, 9.06%). Significant differences in the prevalence of combined overweight andobesity were observed between children residing in high and low socioeconomic areas, by ages and between boysand girls.Conclusion or application: The prevalence of childhood obesity is high and appears more prevalent in girls, inchildren residing in low-income areas and at specific ages. Determinants of the observed differences will need to beinvestigated in order to address the higher prevalence of childhood obesity in high-risk population groups.

Key words: childhood obesity, high risk, paediatric, prevalence, prevention, socioeconomic status.

INTRODUCTION

The prevalence of childhood obesity is increasing rapidly inmost Western countries, and is reported to have reachedepidemic levels.1–3 In the period between 1985 and 1997,

the prevalence of combined overweight and obesity amongchildren is more than doubled, with 19–23% of Australianchildren classified as overweight or obese.4 This is alarmingin a public health context as childhood overweight andobesity have significant immediate and long-term healthconsequences, including the persistence of obesity intoadulthood which has been reported in 25–50% of cases.5

Primary prevention of overweight among children, prior tothe development of risk factors for chronic disease, is there-fore a critical step in stemming the spread of the obesityepidemic.1,6,7

In order to respond appropriately at the local level, anassessment of children’s weight status is important.8 Locally,the Hunter region did not have representative data on theprevalence of overweight and obesity among children. This

R. Sutherland, MPH, APD, Public Health Nutrition Program Manager,Conjoint Lecturer in Nutrition and DieteticsM. Finch, MPH, Public Health Nutritionist, Conjoint Lecturer in Nutri-tion and DieteticsM. Harrison, Grad Dip Medical Stat, StatisticianC. Collins, PhD, APD, Associate Professor in Nutrition and DieteticsCorrespondence: C. Collins, Room HA12, Hunter BuildingCallaghan Newcastle, NSW 2308, Australia. Email:[email protected]

Accepted May 2008

Nutrition & Dietetics 2008; 65: 192–197 DOI: 10.1111/j.1747-0080.2008.00287.x

© 2008 The AuthorsJournal compilation © 2008 Dietitians Association of Australia

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mailto:[email protected]

is a serious omission given that the Hunter region has beenshown to have higher self-reported levels of overweight andobesity in male and female adults compared with the stateaverage.9 The Hunter region has also been shown to havevery high levels of coronary heart disease,10 which arose inthe context of a lower rate of adult obesity in the populationat the time. An assessment of weight status among childrenacross the Hunter population will help in planning healthpromotion strategies, provide baseline data to evaluate theimpact of prevention initiatives as well as assist in predictingadult weight-related morbidity and mortality,11–13

As limited resources are currently available to develop,implement and evaluate local-level population health strat-egies, there is a clear need to ensure that funds are directedtowards initiatives that are likely to be effective and resultin population health gains. The decision to developpopulation-based strategies or to target high-risk groupsshould be considered within the context of relevant localpopulation data. The present study aimed to enhance popu-lation data by determining the prevalence of overweight andobesity in a sample of Hunter primary school-aged children.An additional aim was to identify which sectors of the popu-lation, such as gender and socioeconomic groups, are with ahigher prevalence of overweight and obesity.

METHODS

Study design

The study was a cross-sectional survey to determine preva-lence in a sample of randomly selected government primaryschools, representing a range of socio-demographic areasand geographical locations,

Sample

The study was conducted in the Hunter region of New SouthWales (NSW), Australia. A random sample of governmentprimary schools was invited to participate. Eighteen schoolswere randomly selected from a list obtained from NSWDepartment of Education incorporating all governmentprimary schools in the Lake Macquarie, Newcastle, Maitlandand Muswellbrook school education areas (n = 228, as atMarch 2004). The sample was generated using SAS statisticalsoftware (version 8.2. of the SAS System for Windows, 2005,SAS Institute, Cary, NC, USA). Prior to randomisationprimary schools were classified by socioeconomic status(SES) and geographical status to represent a socio-demographic and geographical range in order to maximisethe representativeness of the sample. Stratification by SESwas conducted prior to randomisation, with all schoolsgrouped according to SES based on postcode according tothe Socio-Economic Index For Areas. The two upper quar-tiles and two lower quartiles were combined to form twogroups as an indicator of low and high SES.14 Geographicregions were quasi-defined as metropolitan and regional andbased on school education areas, with metropolitan incor-porating all schools in the Newcastle and Lake Macquarie

education areas and regional including all schools in theMaitland and Muswellbrook education areas.

The sampling unit for the present study was an individualschool with the sampling frame consisting of all governmentschools in the Hunter Area. Magarey et al. reported that 19%of 7- to 11-year-old children and 23% of 12- to 15-year-oldchildren are overweight or obese.15 Using this informationand assuming a 95% confidence interval, with a precision of�0.5, we obtained the sample sizes. The estimated samplesizes were then adjusted for the effects of clustering and forthe likely response rate of 48%.16

A recruitment package was sent to school principals out-lining the study and responsibilities of the school. Expres-sion of interest forms were returned by schools willing toparticipate or those requesting further details. Follow-upphone calls were made to each school and individual meet-ings, presentations at staff and parents’ and citizens’ meet-ings and additional phone calls made if deemed necessary bythe school principal. School principals who agreed to par-ticipate gave written consent for the study to occur withinthe school. If the principal agreed to participate, the childrenin year 1 to year 6 were invited to participate in the study.Informed consent was also sought from parents and chil-dren. Participation was voluntary.

Teachers distributed the consent forms and parents weregiven two weeks to complete and return the form. In addi-tion, verbal consent was also sought from children on theday height and weight were measured.

Measures

Height and weight were measured for each child via a stan-dard procedure by trained research staff. Height was mea-sured, to the nearest 0.1 cm using a Harpenden PortableStadiometer (Holtain, Crosswell, UK), with the head in ahorizontal plane and the heels in contact with the verticalbeam after asking subjects to inhale, stretch to their fullestheight while applying gentle upward pressure to maintainthe fully erect position during measurement.17 Weight wasmeasured to the nearest 100 g using A & D electronic scales(Model UC-321, Tokyo, Japan) in light clothing withoutshoes and recorded by trained data collectors. All heightmeasurements were taken by either of the two data collec-tors. Date of birth was collected on the demographic sectionof the survey and exact age was calculated. Body mass index(BMI) was calculated as weight (kg)/height(m)2. Duplicatemeasures were taken from the first two schools only. Datawere collected between August and November 2004.

Overweight and obesity were assessed using the interna-tional BMI cut points, standardised for both age and genderas defined by Cole et al.18,19

Statistical analysis

Chi square (a � 0.05) was used to determine if the propor-tion of children classified as normal weight or overweightand obese differed, based on gender, age, SES or geographi-

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cal location (based on district local government regions) inwhich the children attended school. Results were analysedusing SAS statistical software.

The data were adjusted for clustering prior to analysisbecause of children being more alike within each school andparticularly within each age groups within schools. SAS-callable SUDAAN was used to perform the clustering analysisusing an inflation factor of 4.2. (version 10, ResearchTriangle Institute, Research Triangle Park, NC, USA).

Ethics approval

The study was approved by the Hunter Area Research EthicsCommittee (Approval No. H-797-0404), the University ofNewcastle Human Research Ethics Committee (ReferenceNo. 03/12/10/3.18) and the NSW Department of Educationand Training (SERAP No. 04.46).

RESULTS

Of the 18 primary schools contacted, 17 agreed to partici-pate and measurements were completed in 16 within thestudy period, generating a response rate of 88.9%. Oneschool asked to take part in the data collection process,however, specified a date out of study data collection periodthe following year and was therefore not included. Thesample (n = 16) consisted of eight high-SES schools andeight low-SES schools.

Parental consent was obtained for 2238 children from apossible sample of 5206 (43%). Of these, 2224 children(42.7%) were available on the day of measurement. Themean age among children participating in the study was9.6 years (�1.7 SD). Of these, 49% (n = 1087) were male.While the consent rates for high- and low-SES areas were notdifferent (P > 0.05), the proportion of children participatingon the measurement day who were from high SES was 58%(n = 1286) and 41.5% resided in metropolitan versus 58.5%in regional areas.

Of those measured, 606 (28.4%, CI 25.4–29.1%) wereclassified as either overweight (n = 415, 19.3%) or obese(n = 191, 9.1%) with 71.7% classified as normal weight.Table 1 indicates the results by gender.

The prevalence of combined overweight and obesity dif-fered across the age groups (Table 2), with the highest preva-lence observed in those children aged 12 years (34.9%, CI24.6–46.8%) and the lowest prevalence observed amongchildren aged 10 years (20.8%, CI 15.6–27.3%, P = 0.04).

Over 30% of children were classified as overweight or obeseby age of six years (32.2%) and seven years (32.3%). Furtheranalysis by gender for each age group showed that preva-lence varied according to age for girls (P = 0.018), but notfor boys (P > 0.05).

Table 2 shows the combined overweight and obesityprevalence between high and low socioeconomic groupsoverall. Analysis by gender for each socioeconomic groupshowed that there was a significant association betweenprevalence and SES for boys and girls separately (girlsP = 0.0001, boys P = 0.0003). No significant differenceswere observed in the prevalence of childhood overweightand obesity based on geographical region (Table 2). Analysisby geographical region and gender showed no significantassociations.

DISCUSSION

The present study aimed to determine the prevalence ofoverweight and obesity in a sample of Hunter primaryschool-aged children. Findings indicate that combinedprevalence of overweight and obesity is almost 30%. This isconsistent with other current Australian studies.20–22

An additional aim of the study was to identify sectors ofthe population with higher prevalence of overweight andobesity. Our data indicate that prevalence is higher in girls.This is in contrast to the findings of Booth et al.22 who in astatewide study of school children (K, 2, 4, 6 8 and 10) inNSW found combined overweight and obesity to be similarin boys and girls (25% vs 23.3%). A similar study conductedin Victoria with school children aged 5–6 and 10–12 yearsreports 29% of children falling within the overweight orobese categories with similar proportions of boys and girls ineach age group categorised as overweight and obese.20 Incontrast, a study of four-year olds in South Australia usingthe Cole definitions has found gender differences with acombined prevalence of 21.4% in girls versus 17.3% inboys.23 This is also supported by a study of school childrenaged 7–15 years in Western Australia reporting combinedoverweight and obesity at 23.1% for boys and 30.5% forgirls.21 This suggests that further investigation of thesegender differences is warranted, with physical activity andother factors associated with obesity taken into consider-ation.24 School-based obesity prevention strategies deliveredto all students have also had varying impacts on male andfemale students.25 Despite this, care must be taken to ensurethat the obesity prevention messages focus on the develop-

Table 1 Prevalence of normal weight, overweight and obesity in male and female primary school children across the Hunterregion

Gender Total n Normal weight % Overweight % Obese %Combined overweight/

obese % (95% CI) P

Female 1137 68.5 21.6 9.9 31.5 (25.4–38.3)0.01(a)

Male 1087 75.0 16.8 8.2 25.0 (19.9–31.8)(a) P value tests the difference in prevalence in combined overweight and obesity between boys and girls.

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ment of healthy lifestyle behaviours, rather than bodyweight,to avoid an unnecessary focus on weight loss.

The prevalence of overweight and obesity differed signifi-cantly by age. Although the oldest children in the study hadthe highest prevalence of overweight and obesity, of concernwas the one-third of six- and seven-year olds identified asalready overweight or obese. These rates are considerablyhigher than rates observed in five- to six-year olds in anotherAustralian study conducted at a similar time, with 19–23%of boys and girls, respectively, classified as overweight orobese,20 and could be confounded by differences in thetiming of adiposity rebound. Furthermore, our data indi-cated that in the Hunter region of NSW, age and genderdifferences in the prevalence of combined overweight andobesity exist and the differences may be driven by the ratesin girls. While further study is required to assess the deter-minants of this, it is important to acknowledge that all theage rates are high and that prevention strategies may havegreater success when aimed at younger children. These arelikely to be strategies that target the family and early childcare environment.26

The prevalence of childhood obesity was also observed tobe higher among children from lower socioeconomic areas.This finding is strengthened through the analysis demon-strating that the SES difference in prevalence holds for bothboys and girls. While this trend has been demonstrated inadults, particularly in women,9 data demonstrating an asso-ciation between weight and SES among children are stillcurrently limited. Children attending school in lower-SESareas in the Hunter region were 1.5 times more likely to be

overweight or obese compared with children from higher-SES areas. O’Dea27 also found low SES to be associated witha higher prevalence compared with middle to high SES(26.9% vs 13.9%, P < 0.001). In addition, a recent study bySalmon et al.20 has also shown similar trends with childrenresiding in lower-SES areas also more likely to be overweightor obese than those from higher-SES areas (19% vs 29%).

Australian studies indicate that residents from the lowest-income neighbourhoods have 2.5 times more exposure to fastfood restaurants.28 In addition, studies have shown thatlower-income groups may be less physically active and havepoorer access to footpaths, parks and facilities,29,30 as well aslimited ability to afford sporting registration and other costsassociated with physical activity.31,32 Currently, there is limitedevidence of successful interventions targeting overweight andobesity in children living in lower-SES communities. Thefindings from the present study indicate the need for furtherinvestigation of the determinants of obesity in lower-incomepopulations as a way to inform strategies focusing on improv-ing physical activity and eating environments.

This survey provides important baseline data to monitortrends in the Hunter region of NSW and can also serve todetermine the impact of interventions designed to addressobesity. The present study also highlights that specific popu-lation subgroups within the community deserve particularattention and more targeted obesity prevention strategies.However, further research is required to investigate morefully the determinants of the observed differences. Suchinformation would serve as the next step in identifying effec-tive strategies to address the rise in obesity prevalence.

Table 2 Prevalence of normal weight, overweight and obesity among primary school children by age, socioeconomic status(SES) and geographical region across the Hunter region

FactorTotal

NNormal

wt %Overweight

%Obese

%Combined overweight/

obese % P

Age (years)(a)

6 117 67.8 18.4 13.9 32.2

0.04(b)

7 389 67.7 20.2 12.1 32.38 375 70.9 19.3 9.4 29.19 386 73.1 20.1 6.9 27.0

10 371 79.2 13.8 7.1 20.811 375 73.1 18.3 8.6 26.912 209 65.1 27.5 7.5 34.9

SES(c)

High SES 1286 77.8 15.8 6.4 22.20.02(b)

Low SES 938 65.8 22.6 11.6 34.2Geographic location(d)

Metropolitan 925 71.4 18.7 9.9 28.60.93(b)

Regional 1299 71.9 19.8 8.4 28.2(a) Age in whole numbers represents age up until the day before the next birthday (e.g. 6.0–6.99 years).(b) P value tests the difference in prevalence in combined overweight and obesity across age groups, high and low socioeconomic areas orgeographical regions.(c) SES defined by Socio-Economic Index For Areas which consists of four indexes developed by the ABS. Each index summarises a differentaspect of the socioeconomic conditions of the Australian population using a combination of variables from the Census of Population andHousing. The two upper quartiles and two lower quartiles were combined to form two groups as an indicator of low and high SES.(d) Defined by school education areas with metropolitan incorporating all schools in the Newcastle and Lake Macquarie education areas andregional including all schools in the Maitland and Muswellbrook education areas.



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The present study has several limitations. The responserate of 43% is low; however, it is comparative to otherpaediatric prevalence studies. Timperio et al., Cleland et al.and Watson et al. report response rates of 27–44%, 40% and47%, respectively.16,33,34 The ethical requirement of obtainingactive parental consent has been identified as reducingresponse rates.34 There may therefore be a selection bias,with parents and children at extremes of bodyweight poten-tially not being willing to participate. Furthermore, theexclusion of private schools potentially biases the sampletowards lower-SES groups. Prevalence may potentially beconfounded by pubertal status and hence distort compari-sons with standardised BMI cut points. Despite these andother limitations, the main findings stand when comparedwith similar studies conducted in Australia, that overweightand obesity are now common among primary children andthe issue requires urgent action.

CONCLUSION

The present study provides the first data for childhood over-weight and obesity in the Hunter region, with resultsconsistent with other Australian studies.20,21 These data willallow the impact of strategies aimed at preventing childhoodobesity to be monitored. Evaluation of population-basedobesity prevention remains a key priority, as currently thereis limited evidence available to inform childhood obesityprevention strategies.

The present study demonstrates that women and childrenfrom lower-SES areas may be at higher risk of overweightand obesity. In order to ensure that the health gains achievedover the past 20 years remain, this datum highlights theneed for a population-wide approach to childhood obesityprevention.1 Further, intense efforts that are targeted tohigher-risk groups are clearly needed. The development of aportfolio of strategies that incorporates both the broad popu-lation health approach and specific strategies for those mostat risk will ensure an equitable approach to health promo-tion and childhood obesity prevention.

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Higher prevalence of childhood overweight and obesity in association with gender and socioeconomic status in the Hunter region of New South Wales