Early schooling hours could deprive teenagers of adequate sleep which may lead to poor academic performance, depression and obesity, a new study suggests.
By following dozens of younger and older adolescents for more than two years, researchers were able to determine that the children fell asleep later and their circadian rhythms shifted later as they grew older.
But early school start times interfere with their tendency to sleep later, reducing their total sleep.
The study used activity monitors to track how sleep habits changed in younger and older teens as they grew during a two-year period.
"This is one of the few studies that has tracked sleep behaviour and circadian rhythms over the course of up to two-and-a-half years in the same adolescents," said lead author Stephanie Crowley, an assistant professor at Rush University Medical Centre in Chicago.
The negative effects researchers have found can include poor academic performance, mood disturbances, depression, obesity, and even drowsy driving accidents among older teens.
According the data in the new study, conducted with 94 children in all, children seem fated to get less sleep as they mature.
"There are changes in sleep, even as early as middle school," said Crowley, who was a graduate student in the Brown University lab of senior author Mary Carskadon when the study was conducted.
The typical kid in the study moved to a later sleep/wake cycle with ageing, except during the week, when later waking was not possible, most likely because of early school bells.
However, the 18-year-olds in the study slept dramatically longer on weekdays than they did when they were younger because they had graduated from high school.
The study is one of the few to track individual kids for longer than a year.
For some children, the data show, the shift to a later bedtime without a later wakeup time was especially stark, possibly putting them at a greater disadvantage relative to their peers.
The study appears in the journal PLoS ONE.
