(CNN) -- The rate of body mass index change in children nearly doubled from March to November 2020 compared to the rate of BMI change before the Covid-19 pandemic, according to a study published Thursday in the US Centers for Disease Control and Prevention's report on morbidity and mortality.
The CDC team used a medical record database to compare BMI changes in 432,302 US children between the ages of 2 and 19 before and during the pandemic. BMI is a measure that uses height and weight data to track changes in weight relative to height.
All of the children in the study experienced significant increases in their rate of BMI change during the pandemic, except for children who were underweight, the report found.
The increase was especially high in younger children and those with obesity.
"Preschool and school-aged children, particularly those with obesity, had larger pandemic-associated increases in BMI than did adolescents," wrote corresponding author Samantha Lange, an epidemiologist in the CDC's population health and health care team.
This may be due to closure of many child care centers and elementary schools during the pandemic, which reduced access to healthier food choices and organized exercise programs, according to the report.
In children with obesity, the rate of change was 5.3 times higher during the pandemic, which could lead to significant weight gain, the report said.
During the eight months of the study period, children with "moderate or severe obesity gained on average 1.0 and 1.2 pounds (0.45 and 0.54 kilograms) per month, respectively," the CDC team wrote.
"Weight gain at this rate over 6 months is estimated to result in 6.1 and 7.6 pounds (2.8 and 3.5 kilograms), respectively, compared with 2.7 pounds (1.2 kilograms) in a person with healthy weight."
The authors said the study is the "largest and first geographically diverse analysis" looking at the impact of the pandemic on BMI and the "first to show results by initial BMI category."
The findings, the study team noted, suggest a need for "increased access to efforts that promote healthy behaviors," including BMI screening and coordinated federal and state efforts to "facilitate healthy eating and physical activity."
What families can do
There are evidence-backed ways adults can help address their child's pandemic weight gain (as well as their own).
Get moving. Going outdoors into the fresh air helps bodies of any age. Sunlight helps with sleep, as does a brisk walk, which is also good for your heart. Challenge your child -- who can walk faster? (Psst -- you have to let them win at times.)
There are lots of organized family games and activities you can try -- even if it's merely drawing on the sidewalk for fun. Take a look at this CNN list of 100 things you can do with your kids (or not) to get some ideas.
Pack your house with healthy foods. Kids do what parents do, so be a role model. Take your child grocery shopping and pick out healthy items. Limit the amount of processed foods you bring into the house. When you do serve them as snacks or treats, watch the portion sizes.
Picky eaters and non-veggies lovers can be nudged toward eating vegetables by watching family members enjoy them, and by having a bit on their plate, night after night.
The Mediterranean diet wins awards each year for its health benefits -- lower risk of diabetes, heart disease, dementia and more. It's also good for weight loss and includes many options that appeal to kids, such as food on a stick and veggie pizza (including this recipe for a pie with a cute face).
Turn off the screens, within reason. It's been hard to limit screen time during the pandemic. Even experts who call for limiting screen time get that.
Parents are not allowing children to use electronic devices out of any "bad or malicious thought or neglect. They're doing it because it's an easy fix for a complex situation -- which is a frustrated, hungry, tired child, and a frustrated, hungry, tired parent," said Dr. Wendy Sue Swanson, a general pediatrician and chief of digital innovation at Seattle Children's Hospital, in a prior CNN interview.
"I understand why you do it. I do it, too," Swanson said. "But all of us have to work really hard to realize that it is a super easy solution and the harder way might be better and, in the end, might be more beneficial."
Here's why it's so important: In addition to weight gain and a lack of exercise, studies have shown excessive TV viewing is linked to the inability of children to pay attention and think clearly, while increasing poor eating habits and behavioral problems. Associations have also been shown between excessive screen time and language delay, poor sleep, impaired executive function, and a decrease in parent-child engagement.
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