Teenagers who start the school day really early are likely 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.
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. Geneviève Gariépy, who works at McGil University in Montreal, Canada, wanted to know how earlier school start times might be connected with weight." Overweight in teenagers 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 American and Canadian teens are now overweight. Kids who don't sleep enough may be at higher risk. So Gariépy decided to home in on the effect of school start times. Her team collected start times for 362 Canadian schools. Then they asked students at those schools to give their height and weight. In all, they collected data from nearly 30,000 10-to 18-year-olds. Among 6th-to 10th-graders, those who started school earlier were likely to be slightly heavier for their height. Every 10-minute delay (延迟) in school start time was connected, on average, with a slightly lower weight among students who were the same sex (性别), age and height. However, the difference is slight. Healthy eating and getting enough exercise will play a bigger role in keeping a healthy weight.
Because the study compared kids who already started school at different times of day, 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.
Still, the study is a good start, says Cora Collette Bruener, a doctor at Seattle Children's Hospital in Washington. The findings add to a growing pile (累) of evidence that later school start times might be better for teen health, she says.
