To the Editor: We concur wholeheartedly with Gill and colleagues1 in support of recognising obesity as a public health issue, and we dispute claims that the current problem of obesity is being exaggerated.

Gill and colleagues point out that obesity trends have climbed over decades, and state that 6%–8% of Australian school children are affected.1 While this is a substantial burden of over a quarter of a million children, we also consider that restricting definitions of obese to arbitrary cutoff points may underestimate the problem, given that the entire distribution of childhood weight is increasing, not just the extreme group classified as obese. Adiposity is related to cardiovascular outcomes such as myocardial infarction and stroke in a (curvi)linear fashion. Defining obesity by arbitrary cutoff points is vulnerable to differences between sexes, ethnicity and age, and limits our understanding of obesity-related diseases.

It is well known that cardiovascular risk factors cluster, particularly the adiposity-driven components of the so-called metabolic syndrome. In the Western Australian Pregnancy Cohort (Raine) Study, we have used cluster analysis to identify a group of children at risk of future cardiovascular disease with features of the metabolic syndrome.2 The differences in characteristics are shown in the Box. The “high risk” and “low risk” cluster groups differ widely in terms of not only body mass index, the most widely used measure of obesity, but also waist circumference (a measure of central adiposity), insulin resistance, blood pressure, and levels of triglycerides, high-density lipoprotein cholesterol, total cholesterol (data not shown) and low-density lipoprotein cholesterol (data not shown). Not only the conventionally used 95% confidence intervals, but also the 99% confidence intervals do not overlap for any of these intermediate cardiovascular risk factors. We found that 29% of children were in the high-risk cluster at the age of 14 years2 and a similar analysis suggested that even at age 8 years, 25% of children were at increased risk of future obesity, cardiovascular disease and diabetes.3 C-reactive protein (CRP) level is known to be associated with future cardiovascular diseases in adults,4 and with an adverse metabolic profile in children.5 The “high risk” children had significantly higher CRP levels at the age of 14 years than their low-risk counterparts.

Certainly, the magnitude of this problem, affecting up to a third of our youth, needs to be addressed by government and health-planning bodies. We suggest our approach of cluster analysis will help identify earlier those children at substantially increased risk of cardiovascular and other adiposity-related disorders in Australia.

Features of the cluster groups with respect to components of the metabolic syndrome, showing 99% CIs*

BMI = body mass index. HOMA = homeostatic model assessment (for quantifying insulin resistance). SBP = systolic blood pressure. HDL = high-density lipoprotein cholesterol. * From Huang et al.2 Reprinted with permission from the American Diabetes Association.

To the Editor: There is a substantial volume of evidence from a range of national and state-based surveys illustrating increases in the rates of obesity and overweight among Australian children over the past two decades,1 concurring with trends observed in most developed countries.2 The recent article by Gill and colleagues highlighted questions that have been raised publicly regarding the extent and impact of levels of obesity and overweight among Australian children, including whether trends have been exaggerated.1

To examine these issues using the latest data available, we present data from the three most recent national surveys in which weight and height of Australian children were measured: the Australian Health and Fitness Survey (1985),3 the National Nutrition Survey (1995),4 and the Australian National Children’s Nutrition and Physical Activity Survey (2007).5 We examined overweight and obesity levels among young Australians from comparable age groups at three time points over more than 20 years, using the same internationally accepted definitions of childhood overweight and obesity.

For 1985 and 1995 data, we used the figures reported by Magarey et al in 2001,6 which compared results from the 1985 and 1995 surveys using new standard international definitions to classify overweight and obesity among Australian children and adolescents.7 We calculated body mass index for the 2007 Australian National Children’s Nutrition and Physical Activity Survey using the raw data file obtained through the Australian Social Science Data Archive,8 categorising children as overweight or obese based on the same international definitions used by Magarey et al.6 We based our calculations on the age group common to each of the three surveys: 7–15-year-olds.

As shown in the Box, the prevalence of overweight and obesity in boys aged 7–15 years has risen from 11.0% (95% CI, 10.99%–11.01%) in 1985 to 20.0% (95% CI, 19.97%–20.03%) in 1995 and 23.7% (95% CI, 23.68%–23.72%) in 2007. In 7–15-year-old girls, the prevalence of overweight and obesity has increased from 12.2% (95% CI, 12.19%–12.21%) in 1985 to 21.5% (95% CI, 21.47%–21.53%) in 1995 and 25.8% (95% CI, 25.78%–25.82%) in 2007.

While data from additional time points are required to map national trends more comprehensively, our analysis clearly indicates an upward trend in overweight and obesity levels in both boys and girls aged 7–15 years between 1985, 1995 and 2007. This trend is cause for alarm, given the widely recognised body of evidence on the significant short-term and long-term consequences of childhood obesity.9

Prevalence of overweight and obesity in Australian children aged 7–15 years, 1985–2007

* Data weighted for age, sex and region with the weighting variable in the raw data file obtained from the Australian Social Science Data Archive.8