Trends in the prevalence of childhood overweight and obesity in Australia between 1985 and 2008

Abstract

Obesity in children may be associated with serious physical, psychological and social consequences, and may also increase the risk of premature illness, especially type 2 diabetes,1 and death later in life. Consequently, it is now recognised as a principal childhood health concern in developed nations.2 The belief that the prevalence of overweight and obesity among children globally is increasing exponentially has become a media commonplace. Overweight and obesity are said to be ‘ballooning’, ‘epidemic’, ‘skyrocketing’ or ‘soaring’. Some recent examples from the Australian popular media include the following: The fact that the number of fat children in Australia has trebled in the past 20 years and type II diabetes in our young is skyrocketing has little do with genetics and everything to do with lazy parenting. Quigley A. Parents give kids a fat chance of being healthy. Daily Telegraph (Sydney). 12 July 2004. Research indicates that if childhood obesity rates continue to soar, half of all Australian children will be overweight by the year 2025. Masters C. Working mums—fat kids. Daily Telegraph, 11 January 2007. This belief is often echoed and reinforced by public health experts. A spokesperson for Diabetes Australia was quoted as saying that ‘current Australian data shows [sic] overweight and obesity among children and teenagers are still increasing’ (http://www.smh.com.au/news/national/australian-teen-obesity-getting-better/2008/05/28/1211654124127.html, 29 May 2008), and a public health expert from a leading Australian university was quoted as claiming that Australia has ‘the fastest growing rate of childhood obesity in the world’ (http://www.theage.com.au/news/health/australia-worlds-fattest-nation/2008/06/19/1213770886872.html?page=fullpagecontentSwap2, 20 June 2008). In addition, several studies have used exponential models to quantitatively and qualitatively describe secular trends in the prevalence of childhood overweight globally,3 in Europe,4 and in Australia.5 In 2006, Norton et al.,6 for example, reported that overweight prevalence among Australian children has accelerated since the early 1970s and predicted that it will continue to climb, reaching adult rates by 2035. However, some recent reports have questioned the exponential growth in obesity rates, and some have suggested that we are seeing a plateau in prevalence. A recent Australian report found no significant increase in the prevalence of obesity in Australian children between 2000 and 2006 on comparison of data from two national surveys, with a rise from 5.0 to 5.8%.7 Similarly, recent reports from the United States,8 France,9, 10 Sweden11 and New Zealand12 have noted stabilisation in the rates of childhood overweight and obesity in the last 5 to 10 years. These studies have been based on relatively short-time frames and a small number of studies, but certainly cast doubt on the widespread belief that the prevalence of obesity is continuing to increase. This study aimed to examine trends in the prevalence of childhood overweight and obesity over a wider time frame (1985 to 2008) by collating data from a large number of Australian studies. A systematic review and meta-analysis were undertaken. (Australia$ OR Victoria$ OR ‘New South Wales’ OR Queensland OR ‘Northern Territory’ OR Tasmania) AND (‘body mass index’ OR overweight OR obes$ OR ‘body weight$’ OR anthropometr$ OR thinness OR ‘body constitution’) AND (child$ OR adolescen$ OR preschool). The titles and abstracts were screened by two authors (TO and CM) to identify all potentially eligible papers. If there was doubt as to a paper's eligibility, or the abstract was not available, the full text paper was retrieved. The corresponding authors of eligible studies were then contacted by phone or e-mail and invited to provide raw data for inclusion in the meta-analysis (including age, gender, year of data collection, weight and height). If data were unavailable, authors were asked to provide summary statistics regarding number and percentage of normal, overweight and obese children (using Cole et al.'s13 definition) for each age and gender category. A flow chart of studies included in the meta-analysis is shown in Figure 1. In some cases, published values from the same study differed from publication to publication, and occasionally analysis of raw data yielded values that differed slightly from the published data. In these cases, attempts were made to contact the study authors to clarify the issues. When this was not possible, the following hierarchy was used to decide on prevalence estimates: first raw data, then peer-reviewed studies and finally summary reports. Prevalence estimates for overweight and obesity were calculated based on classifications of children into weight-status categories. Data were analysed in the smallest possible age × sex slice (for example wherever possible, estimates were derived for 9- and 10-year-old boys separately, rather than for 9–10-year-old boys together). However, when the sample size in an age × sex group fell below 40, age bands were combined, and the prevalence then calculated. Where the year of measurement was unclear, it was assumed to be 2 years before the publication date of the study, which was the median difference for those studies in which the date of data collection was known. Prevalence estimates were calculated for boys and girls separately, and corrected for age by regressing them against year of measurement, fitting a fourth-order polynomial and using the residuals in subsequent calculations. The values, therefore, represent the degree to which prevalence estimates were greater or less than expected values for children of the same age and gender. In reporting the results, the residuals have been transformed back into age-corrected prevalence estimates for...