Children Destined to Be Obese Can Be Identified by Age 3.5

Ricki Lewis, PhD

October 04, 2011

October 4, 2011 — A prospective analysis of body mass index (BMI) in 1957 children from ages 5 months to 8 years reveals that an "atypically elevated BMI trajectory" that leads to obesity is identifiable by age 3.5 years.

The study, by Laura E. Pryor, MSc, from the National Institute of Health and Medical Research (INSERM) in Paris, France, and colleagues and reported in the October issue of the Archives of Pediatric and Adolescent Medicine, tracked a subset of the Quebec Longitudinal Study of Child Development.

Three groups of weight gain trajectories clearly emerged: low to stable (54.5%), moderate (41%), and high-rising (4.5%). Plotting age against BMI produces a chart in which the first and second curves run parallel to each other on the x-axis, while the high-rising trajectory veers sharply upward at 3.5 years.

In addition to measuring the children’s height and weight annually to calculate BMI, the researchers interviewed the primary caregiver parents (98% mothers) about a number of factors that might have influenced their children’s pattern of weight gain. These included maternal BMI, breast-feeding, depression, maternal age at the time of the child’s birth, immigration status, and socioeconomic factors (mother’s level of education, household income, and "family functioning" as assessed on a 10-point rating scale).

The researchers calculated early weight gain as weight at 5 months minus weight at birth divided by 5 months. They used a "semiparametric modeling method from raw BMI values at each age" to derive group-based developmental trajectories.

Two maternal factors were significantly associated with probability of children being in the high-rising group: smoking during pregnancy and high maternal BMI. Adjusted odds ratios were as follows: for smoking, 2.28 (95% confidence interval [CI], 1.49 - 4.04); for overweight, 2.38 (95% CI, 1.38 - 4.54); and for obesity, 6.33 (95% CI, 3.82 - 11.85). According to the fetal origins of obesity hypothesis, the lower birth-weight associated with smoking triggers compensatory weight gain in early childhood. The researchers hypothesize that the maternal weight association reflects genetic, epigenetic, and environmental factors.

The new study improves upon past investigations by tracking BMI at nine points in time and by considering perinatal factors in setting the stage for future obesity. A limitation of the study is that the identified risk factors "are not necessarily causal of obesity. Rather, they increase one’s probability of following a developmental pattern resembling the high-rising trajectory."

Arch Pediatr Adolesc Med. 2011;165:906-912. Abstract

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