Estimates of overweight and obesity among samples of preschool-aged children in Melbourne and Sydney.

Abstract

Objective: Childhood obesity is a significant and increasing public health issue. We present results from two cross-sectional surveys from Melbourne and Sydney that sought to estimate the level of overweight and obesity among preschool-aged children.

Methods: In Melbourne, weight and height of 196 children from 12 randomly selected preschools and kindergartens were measured and recorded. In Sydney, data on weight and height of 325 children attending four early childhood centres were extracted from client records. The two studies used the age and gender-specific body mass index criteria for classifying overweight and obesity.

Results: The prevalence of Melbourne preschool-aged children considered overweight was 15.3% for boys and 17.3% for girls, with a further 7.1% of boys and 8.2% of girls considered obese. In Sydney, the proportion of children considered overweight was 15.3% for boys and 26.3% for girls. An additional 8.7% of boys and 8% of girls were considered obese.

Conclusion: There is some evidence that childhood obesity may begin in the preschool years. Intervention programs targeting obesity should be considered for families with preschool-aged children in urban Australia.

Key words: childhood obesity, overweight, preschool-aged children, prevalence.

INTRODUCTION

In Australia, childhood obesity is recognised as a significant public health problem (1) as it is overseas. (2) Over the past 20 years, the prevalence of overweight and obesity among Australian children has increased from 10% in 1985 to between 19% and 23% to date. (3-7)

Public concern about increased levels of childhood obesity contributed to several Australian states holding summits in 2002 to identify strategies to address the problem. (8,9) Childhood obesity increases the risk of mortality and morbidity in adulthood. (10) In addition, children who develop obesity in early childhood are twice as likely to maintain the condition throughout life. (11) Obese children are also more likely to experience ongoing health problems in childhood (e.g. sleep apnoea, asthma, hyperinsulinaemia, muscle and joint problems). (2) A number of longitudinal studies have shown that fatness in later childhood tracks to adulthood. (12,13) A study of 5- to 10-year-old Australian children that measured the stability of body mass index (BMI) Z-scores over time found that the vast majority of children remained in the same BMI category. (14)

Despite an increase in obesity among school-aged children, little is known about the prevalence of overweight or obesity among Australian children under the age of six years. Until recently, there was lack of consensus among health professionals about the definition of overweight and obesity for this age group. International BMI cut-off points have now been developed for the 2- to 18-year-old age group that correspond to the adult definitions of overweight and obesity. (15)

To estimate the level of overweight and obesity in Australian preschool-aged children, we present the results of two cross-sectional surveys of young children from Melbourne and Sydney. As these two data sets were collected independently, the procedures for data collection differ. However, both studies targeted preschool-aged children. BMI, as an index of weight for height, was used to estimate overweight and obesity for both surveys. The two sets of data were collected in a reasonably similar time period (1996-97 for Melbourne data, 1998 for Sydney data). We used the international BMI cut points to calculate the prevalence of overweight and obesity among both populations of preschool-aged children. (15)

STUDY DESIGN AND DATA COLLECTION METHODS

Study 1 -- Melbourne

Study design and study population

The study design was a cross-sectional cluster survey of children aged four and five years (age range from 48 to 69 months old with mean age of 57.3 months) from randomly selected kindergartens in Melbourne in 1996-97. The sampling frame was the complete list of 109 kindergartens located in central Melbourne and registered with the Department of Human Services, Victoria. Twenty-one kindergartens were randomly selected using the random number feature of Excel. Invitation letters were sent with details about the study The sample included kindergartens located in areas with various levels of socioeconomic status. Twelve kindergartens (58% of selected and 11% of total) agreed to participate and provided lists of children's name, gender and date of birth. Parents of all eligible children were then asked if they would allow their children to be included in the study. We chose the child whose birthday is the closest to the field measurement date if more than one child from the same family was eligible.

Anthropometry measurements

Weight was measured to the nearest 0.1 kg using standard TANITA digital scales (Model 1609, Tanita Corporation, Tokyo, Japan). Body weight was measured with the child wearing only light clothes and in thin socks or bare feet. Height was measured to the nearest 0.1 cm using a portable height measurer (INVICTA Plastics Ltd, Oadby, England). A single observer (Y. Z.) was used for all measurements.

Study 2 -- Sydney

Study design and study population

The study design was a convenience sample survey of 325 preschool children aged two to four years from four early childhood health centres located in low-socioeconomic suburbs (based on the Social-Economic Indexes for Areas) of the Central Sydney Area Health Service.

Data collection

Weight and height data for the two- to four-year-olds (children born 1994 onwards) were obtained from client records at four early childhood health centres in 1998. The original measurements were carried out by experienced early childhood health nurses and recorded in the client notes. The weights were taken using 'sit-on' scales measuring to the nearest 0.1 kg and the heights were measured without shoes and recorded to the nearest centimetre. The data also included gender and age in months when weight and height were measured.

The studies were approved by The University of Melbourne Human Research Ethics Committee and Ethics Review Committee of Central Sydney Area Health Service.

Data analysis

BMI (=weight (kg) divided by height (2) ([m.sup.2])) was calculated for each child. Each child's BMI was then compared with international cut-off points curve by gender and age for overweight and obesity. (15) Children were classified as overweight if their BMI fell within the cutoff points equivalent to the adult with BMI between 25 and less than 30. They were classified as obese if their BMI was equal or above the cut-off point equivalent to the adult BMI of 30. That is, the number of children defined as being overweight did not include the obese children. Descriptive statistics were calculated using SPSS version 10.0. (16)

RESULTS

In the Melbourne study, 310 children from 12 kindergartens were eligible for the study. We obtained written consent from parents of 261 (84.2%). Two hundred and forty children completed at least one measurement (weight or height) and 196 children completed both measurements. The remaining children were absent on the day, unwilling to be measured or had left the kindergarten. The estimation of the prevalence of overweight and obesity was based on data from 196 participants aged four and five years old.

In this sample of 196 children aged four and five years, 16.3% were overweight and an additional 7.6% were obese. For boys (n = 98), 15.3% were overweight and 7.1% were obese (Table 1). The corresponding figures for girls (n = 98) were higher, with 17.3% overweight and 8.2% obese. Chi-squared test was used and the difference between boys and girls was not statistically significant (P = 0.15).

In the Sydney sample of 325 children, 21.2% of children were classified as overweight and an additional 8.3% were classified as obese (Table 2). For boys (n = 150), the proportion of children classified as overweight and obese was 15.3% and 8.7%, respectively. The proportion of girls (n = 175) classified as overweight was higher than boys (26.3% vs 15.3, P = 0.02), but were similar to boys in the level of obesity (8%).

DISCUSSION

Although these two studies are not directly comparable and have clear methodological weaknesses, they nonetheless suggest that childhood overweight and obesity is already evident in Australian preschool-aged children. The implication of these results is that overweight and obesity prevention programs will also need to include a focus on families with young children and children's care services.

The limitations of study 1 include a small sample size and lack of consideration of design effects. Study 2 suffers from an unrepresentative sampling frame with unknown generalisability and drawing on data from existing records for which the quality is unknown.

However, despite the limitations and the fact that the two studies included children of different ages, the general conclusion remains that there is a relatively high prevalence of overweight and obesity among preschool-aged children. A methodologically rigorous prevalence study is required to calculate an accurate level of overweight and obesity in this population. Further research on overweight and obesity with preschool-aged children will need to focus on developing standard methods for measuring height and weight in this age group for population studies. Otherwise, it will remain difficult to accurately determine the true level of overweight and obesity among young children. The clear conclusion from the present study is that to prevent childhood obesity, it is a public health priority that family-based interventions commence early in infancy.

ACKNOWLEDGEMENTS

We would like to thank the participating preschools and kindergartens in Melbourne, and early childhood health centres in Sydney. We would also like to thank Associate Professor Damien Jolley for his advice on the Melbourne study and Lena Obaid for collecting some of the data for the Sydney study.

REFERENCES

1 National Health and Medical Research Council. Acting on Australia's Weight--A Strategic Plan for the Prevention of Overweight and Obesity. Canberra: NHMRC, 1997.

2 Center for Nutrition Policy and Promotion, USDA. Childhood Obesity: Causes and Prevention--Symposium Proceedings October 27, 1998. Washington, DC: Center for Nutrition Policy and Promotion, USDA, 1999.

3 Wilcken DEL, Lynch JF, Marshall MD et al. Relevance of body weight to apolipoprotein levels in Australian children. Med J Aust 1996; 164: 22-5.

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7 Booth ML, Wake M, Armstrong T, Chey T, Hesketh K, Mathur S. The epidemiology of overweight and obesity among Australian children and adolescents, 1995-97. Aust N Z J Public Health 2001; 25: 162-9.

8 Department of Human Services of Victoria. A Healthy Balance: Victorians Respond to Obesity 23-24 October 2002. (Cited 13 Mar 2003.) Available from URL: http://www.health.vic.gov.au/nutrition/downloads/forumreport.pdf

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12 Power C, Lake JK, Cole TJ. Body mass index and height from childhood to adulthood in the 1958 British cohort. Am J Clin Nutr 1997; 66: 1094-101.

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14 Hesketh K, Wake M, Waters E, Carlin J, Crawford D. Stability of body mass index in Australian children: a prospective cohort study across the middle childhood years. Public Health Nutr 2004; 7: 303-9.

15 Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ 2000; 320: 1-6.

16 SPSS. SPSS for Windows, Release 10.0.0. Chicago: SPSS, 1999.

Yeqin ZUO, (1) Maine NORBERG, (2) Li Ming WEN (1) and Chris RISSEL (1)

(1) Health Promotion Unit and (2) Community Health Services, Central Sydney Area Health Service, Camperdown, New South Wales, Australia

Y. Zuo, MPH, NSW Pap Test Register Manager

M. Norberg, MPH, APD, Community Nutritionist 

L.M. Wen, MD, Senior Research and Evaluation Officer

C. Rissel, PhD, Director

Correspondence: L.M. Wen, Health Promotion Unit, Central Sydney Area Health Service, Level 9, King George V Building, Missenden Road, Camperdown, NSW 2050, Australia. Email: [e-mail]

Table 1 Prevalence of overweight and obesity in children aged four and
five years in Melbourne using international cut-off points for body mass
index

                      Boys (n (%))              Girls (n (%))
Age (years)  n   Overweight (15)  Obese (15)  n   Overweight (15)

4.0-4.4      26   6 (23.1)        1 (3.8)     25   4 (16.0)
4.5-4.9      41   5 (12.2)        3 (7.3)     42   9 (21.4)
5.0-5.4      31   4 (12.9)        3 (9.7)     31   4 (12.9)
Total        98  15 (15.3)        7 (7.1)     98  17 (17.3)

             Girls (n (%))
Age (years)  Obese (15)

4.0-4.4      0
4.5-4.9      6 (14.3)
5.0-5.4      2 (6.5)
Total        8 (8.2)

Table 2 Prevalence of overweight and obesity in children aged 2-4.5
years attending four early childhood health centres in Central Sydney
using international cut-off points for body mass index

                        Boys (n (%))                Girls (n (%))
Age (years)  n    Overweight (15)  Obese (15)  n    Overweight (15)

2.0-2.4       55   9 (16.4)         5 (9.1)     76  20 (26.3)
2.5-2.9       40   7 (17.5)         6 (15)      41  10 (24.4)
3.0-3.4       26   2 (7.8)          2 (7.8)     32   9 (28.1)
3.5-3.9       16   3 (18.8)         0           21   5 (23.8)
4.0-4.4       13   2 (15.4)         0            5   2 (40.0)
Total        150  23 (15.3)        13 (8.7)    175  46 (26.3)

             Girls (n (%))
Age (years)  Obese (15)

2.0-2.4       4 (5.3)
2,5-2.9       4 (9.8)
3.0-3.4       2 (6.3)
3.5-3.9       3 (14.3)
4.0-4.4       1 (20.0)
Total        14 (8.0)