The right amount of sleep is key to proper functioning. But kids who don’t get enough shut-eye can develop mental health issues, according to new findings published in JAMA Network Open by researchers at Norwegian University of Science and Technology (NTNU), reports Norwegian SciTech News.

In a study that examined nearly 800 Norwegian children who were part of a long-term study of nearly a thousand kids between ages 4 and 14, scientists explored the effects of sleep on youngsters’ mental health.

To measure the amount of time children slept, researchers fitted individuals with motion sensors every night for a week and conducted clinical interviews to evaluate mental health problems. These methods were repeated several times every two years.

Findings revealed that children who got the fewest hours of sleep were more likely to develop mental disorders, including anxiety, depression and attention deficit hyperactivity disorder (ADHD). In addition, boys who got less sleep faced an increased risk of developing behavioral issues, while both boys and girls who slept fewer hours were more likely to develop emotional problems.

Researchers also found that as kids got older, the number of those who weren’t getting enough sleep increased. (Specifically, about 3.9% of 8-year-olds, 4.2% of 10-year-olds and 13.6% of 12-year-olds weren’t getting enough sleep.)

Scientists explained that these findings did not necessarily mean that children who didn’t get enough sleep when they were younger would have the same problem when they grew up. In fact, most of them got the recommended amount of sleep. But researchers noted that if kids experienced insufficient sleep starting later, such as at age 10, the habit persisted.

Results also showed that more children didn’t get enough sleep on single nights compared with the number of kids on average who slept too little during a week. About 15.1% of 6-year-olds, 39.1% of 8-year-olds, 45.7% of 10-year-olds and 64.5% of 12-year-olds slept less than seven hours one or more nights each week.

According to Bror M. Ranum, a PhD fellow at NTNU’s Department of Psychology, who is the study’s first author, the quantity of sleep each child needs depends on the individual. What may be considered inadequate sleep for one child may be more than enough for another.

Since most kids outgrow their bad sleeping habits, parents shouldn’t be too concerned, researchers said. But they advise parents who notice that a lack of sleep is affecting their child’s mood or ability to concentrate to make necessary adjustments to their youngster’s sleep schedule, such as having a consistent wake-up time.

For related coverage, read “Study: Sleep Could Help Teens Cope With Discrimination” and “Lack of Sleep Among Teens May Lead to Future Heart Troubles.”