Teens and preteens who start the school day really early tend to weigh slightly more than those who start later. That's the finding of a new study of nearly 30, 000 Canadians between the ages of 10 and 18. These data are the latest evidence that starting school too early can harm health.
"We know from earlier studies that when school starts too early, kids can't get the sleep they need," says Genevieve Gariepy. She works at Mcgill University in Montreal, Canada. Getting too little sleep can put kids at risk for a number of problems. Sleepy teens are more likely to be overweight, to have trouble concentrating and to struggle in school. They also are at higher risk of feeling depressed, using alcohol or drugs and getting in car accidents.
As an epidemiologist (流行病学家), Gariepy is interested in patterns of disease. She studies teen obesity，or extreme overweight. In this study，she wanted to know how earlier school start times might be linked to weight.
"Overweight and obesity in adolescents is a big problem in North America," she says. The number of overweight kids has grown over the past 30 years. About one in three U. S. and Canadian teens are now overweight or obese. Kids who don't sleep enough may be at higher risk. So Gariepy decided to find more about the impact of school start times.
Her team collected start times of 362 Canadian schools and found that among "6 to 10" graders, those who started school earlier tended to be slightly heavier for their height. Every 10-minute delay in school start time was linked, on average, to a slightly lower weight among students who were the same sex, age and height. But it's not clear that changing school start time would help heavier kids lose weight. To know for sure, researchers would want to compare the same kids before and after changing to a later school start time.
The most suitable sleep time for school students.
