"We were alarmed by the high prevalence of overweight in children with Down syndrome," said Dr Helma van Gameren-Oosterom, the lead author of the study from the Netherlands Organization for Applied Scientific Research in Leiden.
"Of course we knew that the prevalence of overweight is rising; for Dutch standards a twofold level, however, was not expected."
Previous studies have suggested children with Down syndrome are especially prone to being heavy. But researchers still aren't sure why that is, according to Dr Sheela Magge, an endocrinologist at Children's Hospital of Philadelphia, who was not part of the new study.
Theories have ranged from physiological differences in metabolism or the way the body suppresses appetite to behavioural differences, such as in how much exercise children get, she said, but no studies have been able to pin down the definitive cause.
How the study was done
For the latest study, the researchers compared growth patterns among 659 children with Down syndrome and no other health problems to general data on youth in The Netherlands.
The team used body mass index (BMI) to determine which children were overweight and which were obese. Dr Magge said they're not a perfect measure for children with Down syndrome because their body proportions are different than those of other children, but it's the best available yardstick for now.
Dr Gameren-Oosterom and her colleagues found 25.5% of boys with Down syndrome were overweight and 4.2% were obese.
Among girls with the condition, 32% were overweight and 5.1% obese, they reported in Pediatrics.
In comparison, children in the rest of the Dutch population had much lower rates: for boys, 12.3% were overweight and 1.7% obese; for girls, 14.7% were overweight and 2.2% were obese.
Dr Magge said researchers have also observed higher rates of overweight among children with Down syndrome in the U.S.
Dr Gameren-Oosterom wrote in an email that she and her colleagues suspect lifestyle has something to do with that pattern. Because it's harder for young people with Down syndrome to develop their motor skills, they may be less active.
Low muscle tone and poor coordination often accompany the disability as well, Dr Magge said.
Keeping strict routines
Her concern with so many kids being overweight is that as people with Down syndrome are living longer, "we may start seeing more complications and comorbidities such as diabetes, cardiovascular disease (and) hypertension, all those things that we worry about in all of our obese adolescents."
Dr Gameren-Oosterom said it's difficult to develop a prevention or treatment strategy to target overweight and obesity in children with Down syndrome, given that the causes are unknown.
But like all youth, she added, those children will benefit from a healthy diet and sufficient exercise.
Dr Magge said people with Down syndrome tend to prefer keeping strict routines, which could be something parents can take advantage of to help instil healthy habits.
"In adults it might be that if they get into a routine of eating healthy it's more likely to stick," she said.
(Reuters Health, November 2012)