Not all children between the ages of 4 and 5 years old take daytime naps, and those who don't tend to exhibit worse psychosocial function.

That's the conclusion of researchers who presented their research this week in Seattle at SLEEP 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies.

Their study did not specifically address why some children stop napping soon after their 4th birthday, lead author Dr. Brian Crosby, from Pennsylvania State University, University Park, said in an email interview with Reuters Health.

"I can tell you anecdotally that the families of non-napping children have various reasons why their children are no longer napping. For example, some children have given up naps naturally; some families don't like their child to nap because it interferes with nighttime sleep; and some families' schedules are so full that there is no regular time allotted for a nap."

He and his associates examined the impact of napping in a sample of 62 children, of whom 23 percent no longer took daytime naps.

Despite the fact that the total 24-hour sleep time did not differ between children who took naps and those who did not, behavioral assessments completed by caregivers showed that non-nappers exhibited significantly more symptoms of hyperactivity anxiety, and depression.

"The results of this study are correlational and do not allow us to make any causal conclusions about the direction of these relationships," Crosby pointed out. "It could be that kids are more hyperactive, irritable, etc. because they don't nap, or are unable to settle down for naps because they are more hyperactive, irritable, etc. This is something important to sort out in future research."

"However, it is possible that napping is important for optimal daytime functioning in children at this period of development."

For now, he recommends that pediatricians ask parents if their preschool-age children are napping or not, and to consider this along with total sleep time and sleep quality when considering problems with sleep and/or daytime functioning.