Dear Mr. Dad: In one of your recent columns you talked about how sleep deprivation can affect women’s fertility. During the summer, my kids get plenty of sleep, but during the school year they’re almost always tired. What are the effects of sleep deprivation on children?

A: There’s no question that sleep deprivation is bad for adults. Besides affecting fertility, is also increases the risk of depression, anxiety, diabetes, cardiac problem, and car accidents (about 100,000/year are caused by drowsy drivers), and decreases our ability to fight off infection. The effects on children are just as bad. Two new studies underscore just how important sleep is by showing how the lack of it influences children’s behavior and food choices.

In the first, researcher Rebecca J. Scharf of the University of Virginia, Charlottesville, and her colleagues found that parents of 4-year-olds who don’t get enough sleep are more likely to report that those children are overactive, angry, aggressive, and impulsive, have tantrums, and exhibit annoying behavior than parents of kids with better sleep habits.

Scharf and her team analyzed data from more than 9,000 children and found that while the preschoolers slept an average of 10.5 hours per night, 11% of them got less than 9.75 hours. (Just so you have a frame of reference, the National Sleep Foundation recommends that kids 3-5 get 11-13 hours/night.) The children who got the least amount of sleep were 80% more likely to exhibit aggressive behavior than the ones who got the most. If you look a graph of sleep and behavior problems, you’d see that as sleep time increases, behavior problems decrease.

Scharf’s study was published in the Journal of Developmental and Behavioral Pediatrics, the official journal of the Society for Developmental and Behavioral Pediatrics. You can read an abstract of it here.

The second study, led by Lauren Hale, an associate professor of preventive medicine at Stony Brook University School of Medicine, looked at a very different age group and a very different kind of behavior. She found that teens who get enough sleep make much better food choices than those who get less. “Not only do sleepy teens on average eat more food that’s bad for them, they also eat less food that is good for them,” said Dr. Hale, in a University press release.

Hale found that the 13,000 teens her team tracked fit into one of three pretty broad categories: “short sleepers,” who got less than 7.5 hours of sleep per night, “mid-range sleepers,” who got 7-8 hours per night, and “recommended sleepers,” who got more than 8 hours per night. (Take the word “recommended” with a grain of salt; The National Sleep Foundation actually recommends that teens get 8.5-9.5 hours per night). As you might expect, the short sleepers were “more likely to consume fast food two or more times per week and less likely to eat healthful food such as fruits and vegetables.”

You can read the full press release from Stony Brook University School of Medicine here.

In another study of teens and their sleeping habits, 90% reported that they get fewer than nine hours a night, and 10 percent said they slept less than six hours.

The effects of sleep deprivation go far beyond children’s behavior in the living room and the kitchen. Like adults, they have a higher risk of depression, anxiety, and mood swings. At school, children who don’t get enough sleep have trouble focusing and concentrating. One study found that teens with C’s, D’s, and F’s got an average of 25 minutes less sleep per night and went to bed 40 minutes later than classmates who were pulling in A’s and B’s. And some experts are now speculating that a large percentage of children with ADHD have been misdiagnosed and that their symptoms are actually caused by lack of sleep.