Sep. 30, 1997 Doctors frequently encounter overweight children in their medical practices. But without hard data to help predict whether a particular child will remain overweight, it's difficult for doctors to know whether they should label a child as overweight and intervene with advice on nutrition and activity.
Now, intuition has been bolstered by numbers from a study in last week's New England Journal of Medicine. The research shows a child's chance of obesity in adulthood is greatly increased if he or she has at least one obese parent.
The study examined the health records of more than 800 young adults aged 23-29, taking their height and weight measurements starting at birth. Height and weight measurements were also taken from their parents' medical records. All were members of Group Health Cooperative of Puget Sound, a large Seattle-based health maintenance organization.
"This study quantifies the conventional wisdom that obesity is a familial trait," said Dr. Robert C. Whitaker, who led the study while on the University of Washington School of Medicine faculty and who is now an assistant professor of pediatrics at Children's Hospital Medical Center in Cincinnati. "It is well-known that being obese as a child increases the risk of becoming an obese adult, but our study shows that having an obese parent dramatically increases that risk."
"There's also a flip side to these results," said co-author Dr. Jeffrey A. Wright, UW associate professor of pediatrics and chief of the General Pediatric Service at Children's Hospital and Medical Center in Seattle. "Children who are overweight in the first three years of life but have normal-weight parents aren't likely to become obese adults. We shouldn't label them as being at risk."
For a child under age 10 -- whether obese or not -- having an obese parent more than doubled the risk of being obese as an adult: an obese 3- to 5-year-old with normal-weight parents had about a 25 percent chance of being obese as an adult; a similar child with an obese parent had more than a 60 percent chance of being an obese adult.
The researchers found that obese and non-obese children under age 3 have almost equally low chances (about 1 in 10) of becoming obese adults if they have normal-weight parents. However, if a parent is obese, the risk of being obese as an adult almost triples for the non-obese toddler, and quadruples for the obese one.
"Early childhood is probably a critical time for intervening," said Wright. "You have to treat the whole family. You can't treat the child out of the family context."
By the time children reach their teens, the likelihood of obesity is less dependent on the parents' weight status. The normal-weight 15- to 17-year-old with normal-weight parents has only a 5 percent chance of being obese 10 years later, and this chance increases to only 14 percent if a parent is obese.
Obese teens have a better than 50 percent chance of becoming obese adults, even if neither parent is obese. The chances increase to 70 to 80 percent if a parent is obese.
The study did not address the question of whether nature or nurture causes obesity. "The risk is transmitted from parent to child by both the genes and the family environment, but whatever is passed on to the child is often expressed by adolescence," said Whitaker.
"This study is not meant to suggest that the children of obese adults will inevitably grow into obese adults," he cautioned. "It suggests, instead, that early and ongoing efforts should be made with these children and their families to prevent obesity from ever developing."
The researchers were conservative in their definition of obesity, using a body-mass index (BMI) of 27 as the threshold. By this standard, 16 percent of the young adults in the study were obese. BMI is calculated by dividing the weight in kilograms by the square of the height in meters. A 5-foot 6-inch woman weighing about 165 pounds has a BMI of 27, as does a 6-foot man of about 200 pounds. Health problems like diabetes and high blood pressure become more common at a BMI of 27 and above.
The long-term Group Health members in this study came largely from white, well-educated families. "From this study, we can't draw conclusions about other groups," Whitaker said. "However, we found that when the young adults in this study were teens, 30 percent of their middle-aged parents were obese. This is consistent with current rates of adult obesity in the United States."
In addition to Wright, co-authors are Dr. Margaret S. Pepe and Kristy D. Seidel of the Fred Hutchinson Cancer Research Center and Dr. William H. Dietz of the New England Medical Center. The research was supported by a Robert Wood Johnson Foundation Generalist Physician Faculty Scholars Award to Whitaker and a grant to Dietz from the National Institutes of Health.
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