'Night owl' girls more likely to gain weight: Study

Teenage girls who prefer to go to bed late are more likely to gain weight, compared to same-age girls who go to bed earlier, warn researchers.

For the study published in the journal JAMA Pediatrics, a total of 804 adolescents -- 418 girls and 386 boys aged between 11 to 16 -- were analysed.

The children responded to questionnaires on their sleep habits and wore an actigraph - a wrist device that tracks movement, said researchers from the Kaiser Permanente, a healthcare company in the US.

During the study, the research team measured the participants' waist size and calculated their proportion of body fat using a technique called dual-energy x-ray absorptiometry.

They also estimated the children's social jet lag -- the difference between their weeknight and weekend bed-times. Those who stayed up far later on weekends than weeknights were considered to have high social jet lag.

According to the study, for girls, staying up late was associated with an average 0.58 cm increase in waist size and a 0.16 kg/m2 increase in body fat.

Each hour of social jet lag was associated with a 1.19 cm larger waste size and a 0.45 kg/m2 increase in body fat.

These associations were reduced, but still remained, after the researchers statistically adjusted for other factors known to influence weight, such as sleep duration, diet, physical activity and television viewing.

Although the researchers found slight associations between these measures and waist size and body fat in boys, they were not statistically significant.

The researchers concluded that improving sleep schedules may be helpful in preventing obesity in childhood and adolescence, especially in girls.