Toddlers who miss daytime naps show more anxiety, less joy and interest and a poorer understanding, reveals study led by University of Colorado Boulder Assistant Professor Monique LeBourgeois.
The results indicate insufficient sleep alters the facial expressions of toddlers - exciting events are responded to less positively and frustrating events are responded to more negatively, she said.
"Many young children today are not getting enough sleep, and for toddlers, daytime naps are one way of making sure their 'sleep tanks' are set to full each day," she said.
"This study shows insufficient sleep in the form of missing a nap taxes the way toddlers express different feelings, and, over time, may shape their developing emotional brains and put them at risk for lifelong, mood-related problems," she explained.
LeBourgeois and her colleagues assessed the emotional expressions of healthy, nap-deprived toddlers one hour after their normal naptime, and tested them again on another day following their normal nap.
The study, believed to be the first to look at the experimental effects of missing sleep on the emotional responses of young children, indicates the loss of a nap - in this case in just 90 minutes - may make toddlers unable to take full advantage of exciting and interesting experiences and to adapt to new frustrations, she said.
"Just like good nutrition, adequate sleep is a basic need that gives children the best chance of getting what is most important from the people and things they experience each day," said LeBourgeois of the integrative physiology department.
The study showed nap-deprived toddlers completing the solvable puzzles had a 34 percent decrease in positive emotional responses compared to the same children completing similar puzzles after their usual midday naps.
The study also showed a 31 percent increase in negative emotional responses of nap-deprived toddlers when they attempted to complete unsolvable puzzles when compared with puzzle-solving attempts after they had napped.
In addition, the study found a 39 percent decrease in the expression of "confusion" when nap-deprived toddlers attempted to put together unsolvable puzzles.
The findings will be published in an upcoming issue of the Journal of Sleep Research.