Researchers at the Harvard School of Public Health looked at data from seven studies that included more than 10,000 kids ages 5 to 12 in the United States, Canada and Japan. In all but one of the studies published between 2005 and 2013, the findings suggested that weight gain accelerated among kids during the summer — mostly for black and Hispanic youngsters and children and teens who were already overweight.
"It's especially those kids who are already at risk who are the most at risk during the summer," said Rebecca Franckle, a Harvard doctoral student who led the study published in the journal Preventing Chronic Disease.
In one study of more than 5,300 kindergarten and first-graders in 310 U.S. schools, researchers found that the kids' body mass index growth, one measure of excess weight, was more than twice as fast during summer vacation as during the school year.
"Although schools may not provide ideal environments for healthy BMI growth, it appears that they are healthier than most children's non-school environment," researchers concluded in the 2007 study in the American Journal of Public Health.
About a third of children and teens in the U.S. are either overweight or obese, according to federal health estimates. Piling on extra weight at a young age can lead to serious health problems later in life.
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