Obesity has become a major national and global public health challenge in recent years. The Health Survey for England 2009 (NHS Information Centre, 2010) reported that 31 per cent of girls and 28 per cent of boys aged two to 15 years were classified as either overweight or obese. Serious complications of obesity in children and adolescents, with long-term consequences, include lipid abnormalities, type 2 diabetes, raised blood pressure, sleep apnoea, polycystic ovary syndrome and orthopaedic problems. An audit of the prevalence of obesity in looked after children in the London borough of Camden was conducted to identify whether obesity is a health concern for this vulnerable group.
Identification and classification of overweight and obesity
Body mass index (BMI) is a measurement of weight adjusted for height and varies with body proportions, age and puberty status. The main limitations of the BMI are that it does not distinguish between fat and muscle mass and it may not reflect fat distribution, therefore caution is required in its interpretation. For practical purposes, BMI is internationally accepted as the most useful measure of obesity and overweight in children, provided values are related to reference standards for age (RCPCH/ National Obesity Forum, 2002; SIGN, 2003; NICE, 2007). Waist circumference may be used to give additional information (NICE, 2007).
There is no universally accepted classification system for childhood obesity and percentile cut-off points are largely based on arbitrary decisions which are not based on known health risks (NICE, 2007). SIGN (Scottish Intercollegiate Guidelines Network) guidelines define overweight as a BMI above the 91st centile and obesity as a BMI above the 98th centile on the UK 1990 charts. In the US and Australia BMI thresholds of the 85th and 95th percentiles are used for overweight and obesity respectively; these have been designated as international standard cutoff points in children and are used in population studies.
For clinical purposes, NICE recommends the use of the UK 1990 BMI charts (Child Growth Foundation) which show the 91st, 98th and 99.6th centile lines. At these cut-off points, sensitivity and specificity are sufficiently high, and serial measures of BMI plotted on the chart can assess changes over time (Reilly et at, 2002).
The International Obesity Task Force (IOTF) defines adults as overweight above a BMI of 25kg/[m.sub.2] and obese above a BMI of 30kg/[m.sub.2]. It proposes corresponding paediatric cut-offs and IOTF reference curves for overweight and obesity are superimposed upon the UK BMI charts. A BMI of 25 corresponds approximately to the 91st centile and a BMI of 30 approximately to the 98 to 99.6th centile.
Looked after children (LAC) frequently have health problems when they enter care. There has often been a history of abuse and neglect and the popular image is of a malnourished and underweight child. We wanted to know whether obesity is as significant a problem in our population of LAC as it is in the general population.
We undertook a retrospective cross-sectional study of LAC in the London Borough of Camden. All children aged over two years at the time of their last statutory health assessment, who were in care in November 2008, were selected. Height and weight at the most recent health assessment and information on age, gender and duration in care were obtained from health records. Data were compiled in Excel and the BMI calculated for each child using the formula BMI = weight (Kg)/height ([m.sub.2]). BMI measurements were plotted on UK 1990 BMI charts. The International Obesity Task Force (IOTF) reference curves for the classification of overweight and obese...