Are we overdiagnosing obesity in preschool children?

摘要

Recent surveys have found almost a quarter of children at school entry to be overweight or obese, leading to suggestions that this is where preventive interventions should be focused. However, others dispute this, as tracking of body mass index (BMI) from preschool age is weak, with 63% of obese toddlers reverting to overweight or healthy weight at later ages,1 while BMI z scores relate weakly to adiposity in younger compared with older overweight children.2 This paper explores the possibility that this lack of persistence of early obesity may be the result of a classification artefact. This issue arose when an obese toddler, seen by a specialist, was reported to have improved, despite no change in BMI. The explanation for this was evident on the BMI chart. This is illustrated with a fictitious example in figure 1, where a child’s centile normalises over time, despite no reduction in BMI. We are used to the idea of children catching down towards normality, as other children grow taller or heavier around them, as the whole growth curve rises over time. However, here the median BMI is the same at both ages. Can it be right that extreme BMI centiles are crossed at so much lower levels in younger children than in mid-childhood, when the average BMI is not increasing? Figure 1 A boy aged 3 with a BMI of 20 is close to the 99.6th centile (severe obesity). If he remains with the same BMI until the age of 9, by then he is within the normal range. Over the same period, the median BMI has not risen and BMI is 25% above the median at both ages. BMI, body mass index. We still have no properly validated upper threshold for unhealthy BMI in childhood. The upper thresholds for healthy adult BMI.