Women who smoke during pregnancy and are overweight early in pregnancy are more likely to have children who become obese as toddlers, and these children will stay obese through their teenage years, according to a new study.
Obesity rates have more than doubled among U.S. children and quadrupled among U.S. adolescents in the past three decades, according to the Centers for Disease Control and Prevention. One in every three young people is obese.
The authors of the new study looked at how children's body mass index (BMI), a measure of weight in relation to height, changed over time, from age one to age 18. They found being consistently obese was associated with certain exposures in the womb, and with having asthma and other problems in adolescence.
Past studies looking at risk factors for obesity and the consequences of being obese have focused on weight at one point in time, Dr. Wilfried Karmaus said.
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"The main difference to previous studies is that we didn't assess obesity at one static moment in time but the development over time," Karmaus, from the School of Public Health at the University of Memphis in Tennessee, said.
He and his colleagues analyzed data from the Isle of Wight birth cohort, based in the UK and originally designed to study asthma and allergies.
They tracked 1,456 infants born between January 1989 and February 1990 until they were 18 years old. Height and weight were measured at ages one, two, four, 10 and 18 years.
The researchers found children's BMIs, as they grew up, fit into four distinct patterns, or "trajectories."
As Karmaus explained, "We have an early persistent obesity group which starts very early and you can detect this group before the age of four years."
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Then there was a "delayed overweight" group of kids who became heavy a little more slowly, and an "early transient overweight" group in which kids were heavy as babies, but had a more normal weight when they were older.
The fourth trajectory included kids who had a normal weight throughout childhood.
"These four groups - we can detect them before the age of four years, this was one of the surprises we had," Karmaus told Reuters Health. "The development is probably set in stone by the age of four years."
About 4 percent of the children studied fell into the early persistent obesity trajectory, 12 percent were in the delayed overweight trajectory and 13 percent were in the early transient overweight trajectory. Roughly 72 percent of kids fell into the normal trajectory, according to findings published in the Journal of Epidemiology and Community Health.
Having a mother who smoked during pregnancy was a strong risk factor for being in the early persistent obesity trajectory. So was having a mother who was overweight early in pregnancy, which suggests children may "inherit" obesity through the type of metabolism they acquire in the womb, Karmaus said.
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Evaluating the children when they were 18, he and his colleagues also found that those in the early persistent obesity group had twice the risk of asthma and higher blood pressure than normal-trajectory children.
The study "provides further evidence to support the importance of prevention of childhood obesity," Dr. Youfa Wang told Reuters Health in an email.
Wang, from the University at Buffalo, State University of New York, has studied childhood obesity but was not involved with the new research.
"Overall previous research has suggested that about one-third of overweight and obese children and about one-half of overweight or obese adolescents would become overweight or obese adults," Wang said.
The new findings are consistent with those from earlier studies, he added.
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"Knowing children's BMI will help parents and children to monitor their weight status and related health behaviors such as eating and exercise, and help make related behavioral changes to maintain a healthy weight," Wang said.
Suggestions to start childhood obesity prevention very early on may actually mean that prevention needs to start with the pregnant mother, Karmaus said.
Parents can also make sure kids themselves are moving around enough as toddlers, and not wait until they're older to address weight issues.
"I think it's important to identify the trajectories early on because at that time the child's metabolism may still be plastic and can be changed, but later in life, obesity prevention is very difficult," Karmaus said.
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