Introduction

The rising prevalence of being overweight and obese is well recognised. According to the World Health Organization (WHO), 1.2 billion people are overweight, 300 million of whom are obese (Government Office for Science, 2007). The most startling increases have taken place in the US and UK where the prevalence of overweight and obesity has almost doubled in the last 25 years (Wardle and Boniface, 2008). These increases are not just confined to adult populations. Data from the Health Survey for England, using the UK national body mass index (BMI) percentile classification, indicates that the prevalence of overweight (including obesity) among 2- to 10-year-olds rose from 23% in 1995, to 28% in 2003, with the prevalence of overweight and obesity, and the rate of increase, being similar for boys and girls (Jotangia et al, 2005). These secular changes appear to be accelerating (Stamatakis et al, 2005; Jackson-Leach and Lobstein, 2006), and the age at onset of obesity is occurring at ever younger ages.

The health problems associated with adult obesity are well described and include type 2 diabetes, hypertension and coronary artery disease, sleep apnoea, pulmonary hypertension, hepatobiliary disease, cancers and reproductive and musculoskeletal disorders (Kopelman, 2007). Childhood obesity also has major implications in the short term for child health, development and well-being, and in the longer term for health in young and later adult life. However, the consequences of an increasingly early onset of childhood obesity are less clear (Reilly et al, 2003). Kimm and Obarzanek (2002) have consequently emphasised the need for prospective studies to delineate the morbidities associated with childhood obesity. Data from the Millennium Cohort Study (MCS) provide the ideal opportunity to examine the development of obesity and its consequences from a very young age.

Tackling childhood obesity is a priority for the UK government, given the substantial rise in obesity and overweight among very young children. In 2007, a long-term public service agreement (PSA) target for addressing childhood obesity was set, with the aim to ‘reduce the proportion of overweight and obese children to 2000 levels by 2020 in the context of tackling obesity across the population’ (HM Government, 2007)