Birth weight is an important factor in whether a child becomes obese or develops insulin resistance at an early age. But as the child becomes older, current size and childhood weight gain become increasingly important—lessening the effect of birth size—new research in Hypertension suggests.

Researchers from the University of Valencia in Spain assessed the association of birth weight and childhood growth patterns on cardiometabolic risk factors in a cohort of full-term newborns up to age 10. They followed 145 white subjects (73 girls) through five years and 100 (52 girls) through 10 years. The children who completed follow-up through 10 years had similar baseline characteristics to the overall study population.

“Careful observation of the cardiometabolic consequences of intrauterine growth and development during the first years of life is important to the promotion of strategies that reduce adverse effects and contribute to the improvement of health,” lead author Empar Lurbe, MD, PhD, and colleagues wrote. “Among others, a major reason for beginning early prevention is that the prevalence of obesity has increased even among preschoolers, many of whom remain obese into adolescence.”

Three categories of birth weight were considered: small for gestational age (SGA), appropriate for gestational age (AGA) and large for gestational age (LGA). SGA was defined as birth weight below the 10^th percentile for sex, AGA included newborns between the 10^th and 90^th percentiles and LGA included all participants above the 90^th percentile.

Birth weight was a strong predictor of obesity at both 5 and 10 years old. Compared to LGA newborns, AGA babies had a 46 percent reduced risk while SGA had a 78 percent reduced risk of developing obesity by age 5. At age 10, the risk reductions were 23 percent for AGA and 75 percent for SGA.

In addition, Lurbe et al. found 22 children at age 10 had fasting insulin values above 15 international units per liter (U/L), a threshold for defining insulin resistance pre-puberty. Eleven of the subjects became insulin resistant between ages 5 and 10, with the development of obesity increasing that likelihood by a factor of 2.6.

“To the best of our knowledge, this is the first longitudinal study starting at birth and extending to the end of the first decade of life that analyzes the changing impact of BW (birth weight) and current size on cardiometabolic risk factors, assessing the early factors associated with becoming obese or developing insulin resistance,” the authors wrote. “The main findings are that the association of current body size on cardiometabolic parameters increases over the years, partially blunting the potential effect of BW. Although the risk of becoming obese at 5 years is directly related to BW, is boosted by maternal obesity and is partially dampened by breastfeeding, and at 10 years, maternal obesity is the only factor related to the risk for obesity.”

Lurbe and colleagues pointed out the child of an obese mother may have been exposed to a “suboptimal in utero environment” and might experience an unhealthy lifestyle growing up. Identifying at-risk childhood populations is important, they said, because puberty—with its substantial metabolic and hormonal changes—has the potential to exacerbate pre-existing factors and set an individual on a dangerous path.

“Our data reinforce the necessity of considering the risk to develop obesity and the presence of an early clustering of metabolic risk factors that are linked to a fast weight increment during the first years of life,” Lurbe et al. wrote. “This opens a timely window of opportunity in childhood healthcare.”