The vast majority of children who were obese at three years of age were overweight or obese in adolescence, a study from Germany has found.

Anonymised biometric data were collected by paediatricians from children who had been seen in both childhood and adolescence (15-18 years) attending for well child and other consultations. Overall, 241,715 data points from 51,505 children were analysed. Overweight was defined as a BMI 1.28-1.87 standard deviations (SD) above overall age-matched population mean BMI. Obesity was defined as a BMI 1.88-4.9 SDs above the mean.

Although just two sets of data were required for inclusion (one in childhood, one in adolescence) many children had been seen several times during childhood. This allowed calculation of BMI and allocation to underweight, normal weight, overweight and obesity at several points over the years, and a trajectory of weight and BMI change ascertained.

A retrospective analysis found that 53% of obese adolescents had been overweight (22%) or obese (31%) at age five years. The trajectory of obesity rose steadily each year in these children from age two through to adolescence. The greatest acceleration in BMI SD score occurred between ages two and six years.

The probability of overweight or obesity in adolescents was greater in those whose BMI score had accelerated during their preschool years compared with those having a stable BMI score (28.6% vs 20.0%) RR 1.43 (95% CI: 1.35-1.49). The majority of normal weight adolescents had never been overweight.

A prospective analysis looked at how many obese children went on to become obese adolescents. This showed that almost 90% of children who were obese at age three were overweight or obese as adolescents. Only a minority were of normal weight at ages 15-19.

Children who were born large for gestational age also had consistently higher BMI scores during childhood and adolescence. Nearly half, 43.7%, compared with < 30% of normal birthweight children, went on to become overweight or obese adolescents; RR 1.55 (95% CI: 1.38-1.74, P < 0.001).

Children born to mothers who were overweight or obese also tended to have higher BMI scores in childhood and adolescence.

The majority of overweight or obese teenage children will become overweight or obese adults. The crucial time to spot individuals becoming overweight or obese would appear to be between two and six years of age.

The author of an accompanying editorial¹ states: ‘The identification of a critical window for predicting childhood weight gain provides an opportunity for intervention to prevent obesity in children at risk. ‘The finding that the risk of adolescent obesity manifests by three to five years of age suggests that nutritional counselling should be considered when exaggerated weight gain persists or emerges after two years of age; it would be of value to test the efficacy of early dietary intervention in an appropriate trial. ‘Counselling could be applied pre-emptively for families in which the parents are overweight, particularly if there is a history of maternal diabetes or smoking,’ he adds.

Dr Chris Barclay