If your child is showing signs of depression, it might not be based on lack of friends or difficulty in school. It might have to do with something you never thought of... sleep.

A new study by researchers at the University of Pittsburgh, published in the January 1, 2007, issue of Sleep magazine, found that kids with sleep problems have more signs of depression and anxiety than kids who sleep through the night.

The researchers studied 553 depressed children and found that almost three-quarters of the children had sleep problems – 53 percent had insomnia alone (too little sleep), 9 percent had hypersomnia (too much sleep), and 10 percent had both. The age of the children didn't seem to make much difference, but girls with depression were more likely to have sleep problems than boys.

What was most interesting about the study, was the finding that not just too little sleep, but too much, can be a problem. Plus, children who suffered from both depression and a sleep disorder were more severely depressed and stayed depressed longer.

If your child seems depressed, you should talk about it with your family doctor, but you should also talk about their sleep habits. How much sleep is the right amount? Experts say that children in grammar school should get 10 to 11 hours of sleep a night, while preschoolers should sleep 11 to 13 hours a night. If your kids aren't logging in those kind of hours, make sure you mention it to your physician, and consider seeing a sleep specialist. Because lack of sleep, or too much of it, can be a predictor of depression.