Children who have excess body fat by age 10 may have greater odds of developing diabetes in their preteen years than their slimmer peers, a Canadian study suggests.

Researchers measured height and hip size to assess body fat in about 600 children when they were 8 to 10 years old, and again two years later. They found every 1 percent of additional body fat at the start of the study was linked to a 3 percent decline in sensitivity to the hormone insulin, a shift that can allow excess sugar to build up in the blood and lead to diabetes.

The study published in JAMA Pediatrics also found more exercise and less screen time were linked to better insulin sensitivity, which might reduce the risk of diabetes. Reduced body fat might explain at least part of this connection, said lead study author Dr. Melanie Henderson of the University of Montreal.

"Our findings suggest that we should be encouraging children early on to be physically active, and that we should reduce their screen time, in order to favor a healthy body weight and better cardiometabolic health later on in life," Henderson said by email.

Henderson and colleagues focused on what's known as insulin sensitivity, the body's ability to use this hormone to regulate levels of blood sugar, or glucose, and turn it into fuel for cells. Type 2 diabetes is associated with obesity and occurs when the body can't make or use enough insulin to prevent glucose from accumulating in the blood.

Researchers assessed children once when they were 9.6 years old on average, and again two years later. The majority of the kids had not gone through puberty at the start, and by the end of the study two thirds had experienced this transition.

All of the children had at least one obese parent, and 23 percent of the kids were obese themselves at the start of the study. Another 19 percent were overweight.

The children who had more girth around their hips or bigger increases in hip size during the study were more prone to insulin insensitivity than kids with slimmer hips. Examining excess circumference around the hips, a measure known as adiposity, is thought to be better than relying on overall weight to assess fat because it can more accurately account for muscle and flab.

Physical activity seemed to be the main explanation for the differences in childrens' adiposity. Every 10 minutes per day of moderate to vigorous physical activity was associated with 3.5 percent lower body fat at the end of the study, even after adjusting for fitness levels and the amount of screen time. This amount of exercise was also linked to a 4.8 percent increase in insulin sensitivity.

At the same time, every one-hour increase in screen time at the start of the study predicted a 2.9 percent increase in body fat. This amount of screen time was also associated with a 4.5 percent reduction in insulin sensitivity.

One shortcoming of the study is that 66 children, or about 10 percent, dropped out before the end, the authors note. The youth who left the study tended to be more insulin resistant and have more body fat than the children who stuck with it through the end.

Even so, the findings are important because metabolic health during childhood can influence whether people later have health problems including diabetes, hypertension, obesity, sleep apnea, heart attacks and strokes, said Dr. Kim Eagle, a researcher at the University of Michigan Frankel Cardiovascular Center in Ann Arbor.

"Daily decisions about activity, screen time, food and beverage consumption and overall energy balance matter and can influence profoundly what our children's future health state will look like," Eagle, who wasn't involved in the study, said by email.

"We live in a toxic culture filled with empty calories, video games, endless screen time opportunities, and not enough health education," Eagle added. "Studies like this one should help us find the will to take action."

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