Page last updated: 19-JUN-2009

Child Health

Childhood BMI Statistics

There is continued concern over the levels of obesity among children in Scotland.  Obesity during childhood is a health concern in itself, but can also lead to physical and mental health problems in later life, such as heart disease, diabetes, osteoarthritis, back pain, increased risk of cancer, low self-esteem and depression.  Obesity develops as a result of an imbalance between energy consumption and energy expenditure.  Scottish Intercollegiate Guidelines Network (SIGN) publication No. 69 provides guidance on the management of obesity in children and young people Link opens in new window(SIGN publication No. 69 - Edinburgh: SIGN, 2003).

The calculation of Body Mass Index (BMI) is one of the most widely used methods for assessing body composition or estimating levels of body fat.  BMI is calculated by dividing an individual's weight (in kilograms) by their height (in metres) squared and gives an indication of whether weight is in proportion to height.

The normal BMI range for children changes substantially with age and is different between boys and girls.  A certain BMI at one age may be the norm but at another age the same BMI may be unusually high or low.  Interpretation of BMI values in children therefore depends on comparison with age- and sex-specific growth reference charts.  These provide thresholds or cut-off points in the BMI distribution (BMI centiles), which can be used to estimate levels of obesity, overweight and underweight in children.  The standard approach in the UK is to use the UK 1990 growth reference for BMI.

These pages look at trends in the proportion of children classified as overweight, obese, severely obese, and underweight according to the UK 1990 growth reference for BMI.  The BMI centile cut-offs used to derive the percentages classified as overweight, obese and severely obese are those recommended in SIGN guidance for the purposes of population monitoring and epidemiological research.  The statistics do not represent the percentage of children clinically classified as overweight, obese or severely obese.  Use of the cut-offs recommended for clinical practice would result in lower percentages for overweight, obese and severely obese and BMI centile would be only one of a variety of factors taken into consideration before any clinical diagnosis is made.