Early-life risk factors for childhood obesity associated with zBMI growth rates

There are a number of risk factors for childhood obesity that can be evident in infancy. Researchers have pointed to behaviours and characteristics such as shorter breastfeeding duration, high birthweight and high maternal body mass index (BMI) as important risk factors related to obesity in early childhood. In a recent study published in the American Journal of Clinical Nutrition, scientists from The Hospital for Sick Children (SickKids) set out to discover whether there are particular time periods during infancy through preschool when BMI growth rates differ according to these three factors. Identifying these periods could lead to timely interventions targeting specific risk factors, reducing the likelihood of obesity later in life.

The researchers examined data from TARGet Kids! (The Applied Research Group for Kids!), a primary care research network in Toronto co-led by SickKids and St. Michael’s Hospital, which collects information from well-child physician visits and allowed the researchers to visualize BMI growth over time. They specifically looked at “zBMI”, a measure of BMI relative to the median BMI of children of the same age and sex according to the World Health Organization (WHO) growth standard. The researchers then used advanced statistical techniques to study specific windows of growth and determine whether growth rates differed during certain periods by the three risk factors identified above.

“Accelerated growth in infancy and early childhood is a strong risk factor for obesity,” says the study’s lead author, Dr. Karen Eny, Research Fellow, Paediatric Medicine Division, SickKids. “If we can identify time periods of accelerated growth we may be able to develop effective targeted interventions at a crucial time in early childhood development.”

Overall, the research team found zBMI growth rate changes were greatest in the first 18 months of life and all three of the risk factors studied were associated with periods of accelerated growth:

• Children who were breastfed for less than six months showed higher growth rates between the first month and 18 months of age, resulting in higher BMI levels from 18 months onward.
• Between one to three months and three to six years of age, all children experience a decline in growth rates. Children born to mothers with BMI levels of 30 or higher showed a slower decline during these two age periods.
• Children who were born weighing four kilograms or more showed slower growth rates in the first three months of life but maintained higher BMI levels at all time points examined from 0-72 months of age.

“Our work has shown that the differences in zBMI observed in early infancy can and do persist at later stages of childhood,” says the study’s principal investigator, Dr. Catherine Birken, Staff Paediatrician and Scientist in Child Health Evaluative Services at SickKids and Associate Professor in the Department of Paediatrics at the University of Toronto. “It’s important health-care providers address these risk factors as early as possible to set children on the best trajectory for their overall health.”

Next, the researchers plan to examine whether there are specific growth periods associated with higher risk of other health outcomes such as elevated blood pressure and cholesterol.

This work was supported by the Canadian Institutes of Health Research (CIHR) Institute of Human Development, Child and Youth Health; the CIHR Institute of Nutrition, Metabolism and Diabetes; the St. Michael’s Hospital Foundation and the SickKids Foundation. It is an example of how SickKids is making Ontario healthier, wealthier and smarter (www.healthierwealthiersmarter.com).