Too much TV can make your kids sick.

There is a strong association between the amount of screen time kids watch and early risk factors for diabetes, Dr Claire Nightingale — a co-author of a study on the topic, published today in the journal Archives of Disease in Childhood — tells Moneyish.

The magic number of hours of daily screen time? Three. More than that, and you’re putting your kids at significant risk. While none of the children in the study had developed diabetes yet (Type 2 diabetes typically begins in adulthood), children who had three or more hours of screen time a day had significantly elevated levels of insulin resistance and leptin, a hormone that controls hunger. Both of these factors increase the risk of developing diabetes in the future, she says.

How much screen time are everyone else’s kids getting?

Amount of screen time watched each day Percentage of children who watched this much
None 4%
Up to 1 hour 37%
1-2 hours 28%
2-3 hours 13%
3 hours or more 18%

Source: Archives of Disease in Childhood; data from 2004-7 sample. 

Nightingale points out that she can’t yet say that the added screen time is causing these elevated diabetes risk factors. Nor can she say that having elevated levels of these risk factors at such a young age will guarantee that you get diabetes. Still, the findings are of “considerable potential public health interest,” the researchers write — and are concerning enough that she says parents should consider reducing the amount of screen time their children get.

It’s confusing to know how much screen time is too much, especially as kids enter school and might need to use a screen for homework. And it doesn’t help that American Academy of Pediatrics changed its guidelines in October. Now, parents of children over six-years-old are to talk to their doctors about screen time and create an age-appropriate plan for each kid; the guidelines for kids ages 2 – 5 are clearer (less than one hour a day) and 18 months and under should get no screen time.

Still, the evidence that screen time can hurt your kids is compelling enough that parents may want to follow the as-little-as-you-can-manage rule. A study of sixth graders from 2014 show that screen time reduces children’s ability to read other people’s emotions; when screens are removed from their lives for just five days, they’re better able to do this. And another study showed a link between screen time use in 6-12 year olds and sleep disturbances, and still others show lowered test scores and less physical activity.