the upper tail. For example, each additional hour of sleep was associated with only a slight reduction in BMI (0.07 kg/m2) at the 10th BMI percentile. In comparison, at the 50th percentile a higher reduction in BMI was observed (0.17 kg/m2), and at the 90th percentile an even greater reduction in BMI was observed (0.28 kg/m2). Importantly, the relationship between sleep duration and BMI remained after adjusting for time spent in front of computer and television screens and being physically activity, leading to the conclusion that more sleep could contribute to the prevention of adolescent obesity, even if national screen time and physical activity guidelines are met.
Based on the results, the authors suggest that increasing sleep from 8 to 10 hours per day at age 18 could result in a 4 percent reduction in the number of adolescents with a BMI above 25 kg/m2. At the current population level, a 4 percent reduction would translate to roughly 500,000 fewer overweight adolescents.
"Educating adolescents on the benefits of sleep, and informing them of sleep hygiene practices have shown to have little impact on adolescent sleep duration," said Mitchell. "One possible solution could be for high schools to delay the start to the school day. Previous research has shown that delaying the start of the school day even by 30 minutes results in a 45-minute per day increase in sleep. Since our study shows increasing sleep by an hour or more could lead to a lower BMI, delaying the start of the school day could help to reduce obesity in adolescents."