Teenage girls who sleep later are more likely to gain weight, compared to those of the same age who go to bed earlier, according to a study.
The research, published in the journal JAMA Pediatrics, looked at the sleep habits of 804 volunteering adolescents — 418 girls and 386 boys — between the ages 11 and 16.
The participants responded to questionnaires about their sleep patterns and wore a wrist device that tracked movement, the study noted.
The researchers, including those from Kaiser Permanente in the US, measured the children's waist size and calculated the proportion of fat in their body.
They also calculated the difference between the children's weeknight and weekend bedtimes — also called the social jet lag.
Children who stayed up far later on weekends than weeknights were considered to have high social jet lag.
Previous studies had found that adults who preferred to stay up late, and had high social jet lag were more likely to gain weight than those who went to be earlier and did not have social jet lag, the study noted.
When the researchers conducted the current study to determine if the same findings would apply to young people, they found that girls, staying up later was associated with an increase in waist size by an average of 0.58 centimetre (cm), and a 0.16 kilogramme (kg) per square metre increase in body fat.
According to the study, each hour of social jet lag was associated with a 1.19 cm larger waist, and an increase in body fat of 0.45 kg per square metre.
The association between sleep time and weight gained was reduced but still remained even after the researchers statistically adjusted for other factors such as sleep duration, diet, physical activity, and television viewing which all influenced weight, the study noted.
However, the associations between these measures and waist size and body fat in boys was not statistically significant, according to the researchers.
The study noted that improving sleep schedules may be helpful in preventing childhood and adolescent obesity, especially in girls.
