By the time they enter sixth grade, many middle-class children sleep so little during the school week that daytime drowsiness may compromise their ability to pay attention and learn, a new study suggests.
This situation derives from a combination of factors, say psychologist Avi Sadeh of Tel Aviv University in Israel and his colleagues. Children tend to fall asleep at increasingly later times as they move from the second to the sixth grade, while continuing to be awakened at the same time for school.
“Our study suggests that the sleep behavior of the older children may not be in accordance with their physiological needs,” they contend. “These children are thus at risk of being chronically sleep deprived.”
What’s more, Sadeh’s team finds that nearly 20 percent of kids in the second, fourth, and sixth grades have serious sleep problems that typically aren’t perceived by either the children or their parents. In the study, sleep disturbances consisted of regularly being awake for at least 10 percent of the night after falling asleep or waking three or more times during the night for at least 5 minutes each time.
Scientists know little about how children develop their sleeping habits. Earlier investigations indicated that sleep disturbances affect about one-third of babies and toddlers. Other sleep difficulties arise as the daily sleep-wake cycle gets pushed back after puberty. Teens who’ve crossed this threshold tend to go to sleep later and, left to their own devices, wake up later than people do at other ages (SN: 9/25/99, p. 205: http://www.sciencenews.org/sn_arc99/9_25_99/bob2.htm).
Grade-schoolers have attracted the least attention from sleep researchers. Sadeh’s group studied 72 boys and 68 girls attending an Israeli public school. Students lived in middle-class or affluent families, most including two parents.
From astronomy to zoology
Subscribe to Science News to satisfy your omnivorous appetite for universal knowledge.
The scientists monitored each child for four or five weekday nights using an actigraph, a device resembling a wristwatch that records body-activity levels. Actigraph data accurately identify periods of sleep and wakefulness and yield estimates of movement, the researchers say.
Children described their sleepiness and alertness in journals. The youngsters and their parents also completed questionnaires about the children’s sleep habits.
Children fell asleep at later times as they got older regardless of their supposed bedtimes. Sixth graders drifted into slumber slightly more than 1 hour after second graders did and about 25 minutes after fourth graders did, the researchers report in the May Developmental Psychology. Sleep quality, such as the number of night wakenings and length of sleep periods, was similar at all grades.
Sixth graders, who started school at the same time each day as the younger kids, cited the most morning drowsiness.
A physiological shift to a later sleep-wake cycle may emerge at a younger age than has previously been reported, Sadeh holds. Increased school demands and social pressures to stay up at night may also stretch out older kids’ waking hours, he says.
Girls slept more minutes per night than boys did, the difference reaching a peak of 24 minutes per night in the fourth grade. Most children in each grade awoke once or twice per night.
Younger parents proved more likely than older ones to enforce early bed times. However, having highly educated parents and relatively little family stress correlated most strongly with children’s sleep quality. Sources of family stress included emotional turmoil, serious illness, and the deaths of close relatives.
Such findings make sense, since kids who feel unsafe in their family or neighborhood often encounter sleep problems, comments pediatrician Ronald E. Dahl of the University of Pittsburgh School of Medicine.
An increasing number of children enter puberty by the sixth grade, which may explain their delayed sleep onset in Sadeh’s study, Dahl says.
“We’re seeing more and more school-age kids who have sleep problems and who doze off in class,” remarks pediatrician Judith Owens, who runs a sleep clinic at Rhode Island Hospital in Providence.
Long-term studies need to untangle the many influences on sleeping habits in individual children, from soda consumption to Internet use at night, Owens holds. “Sadeh’s work is great, but much remains to be done,” she says.