The study involved 519 children who were 7 years old. Their activity was measured for 24 hours by an actigraph that they wore on their waist.
Results show that children who were more active during the day fell asleep faster at night. As their mean daytime “activity count” increased, their time to fall asleep decreased.
Overall, the children took 26 minutes to fall asleep on average. Each hour of daytime inactivity increased the time it took children to fall asleep by 3.1 minutes.
Children who fell asleep faster also slept longer, reports the BMJ Group. Every 11-minute drop in the time it took to fall asleep was associated with an extra hour of total sleep time.
In the journal Sleep in 2008, the same research team published an early analysis of the same sample of 7-year-old children. The study found that their average sleep time was about 10 hours.
Their average bedtime was 8:15 p.m.; their average rise time was 7:07 a.m. Children who went to bed after 9 p.m. slept about 41 minutes less than other children.
On weekend nights the children slept about 27 minutes less than on school nights; although they went to bed about 30 minutes later on weekends, their morning rise time was only slightly later.
There also was a seasonal effect, with children getting the least sleep in summer. They slept about 40 minutes longer in winter, 30 minutes longer in fall and 15 minutes longer in spring.
The study also found that children who slept less than nine hours at night were three times more likely to be overweight or obese. The increased risk remained even after controlling for factors such as TV watching and sedentary activity.
The AASM recommends that school-aged children get about 10 to 11 hours of sleep each night. Learn more about sleep and children on SleepEducation.com.
Image by Elke Noda