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Teenagers who go to bed late are more likely to pile on the pounds, according to new research.

Youngsters who do not sleep at risk of putting on weight

Regularly staying up late could affect young people's weight, a new study has found
Regularly staying up late could affect young people's weight, a new study has found Credit: Photo: Alamy Stock Photo/Posed by model

A five year study found every extra hour they stayed up during the school week added an alarming 2.1 more points to their BMI (body mass index).

And exercise, the amount of time they spent in front of computer or TV screens and the actual number of hours they slept made no difference.

"These results highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management during the transition to adulthood."
Lauren Asarnow

The study of more than 3,300 participants said teenage night owls may want to hit the hay earlier in a bid to combat obesity.

Lauren Asarnow, of the University of California, Berkeley, said: "These results highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management during the transition to adulthood."

BMI is the measure of a person's weight in kilograms divided by the square of height in metres. A healthy adult BMI range is estimated to be 18.5 to 24.9. Above this is considered overweight, and above 30 obese.

The study published in the the journal Sleep analysed data from the National Longitudinal Study of Adolescent Health, which has tracked the influences and behaviours of US teenagers.

It focused on the onset of puberty, the college age years and young adulthood and compared the bedtimes and BMI of the participants from 1994 to 2009.

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Adolescents in the study reported their bedtimes and sleep hours while researchers calculated their BMI based on their height and weight.

Surveys show that many teenagers do not get the recommended nine hours sleep a night, and report having trouble staying awake at school.

The human circadian rhythm, or body clock, which regulates physiological and metabolic functions typically shifts to a later sleep cycle at the onset of puberty.

Ms Asarnow, a doctoral student, added the results suggest adolescents who go to bed earlier will "set their weight on a healthier course as they emerge into adulthood."

She is a researcher on the university's Teen Sleep Study, a treatment program designed to reset the biological clocks of adolescents who have trouble going to sleep and waking up.

Earlier this year a study of 522 people by British researchers suggested people who needed a lie in at weekends to make up for lack of sleep in the week were at greater risk of obesity and type 2 diabetes.

Studies have also shown shift work can rapidly put healthy people into a pre diabetic state. The action of throwing the body clock out of sync is thought to disrupt the natural rhythm of hormones in the body, leading to a host of health problems.

But the pressures of work and social lives mean many people cut their sleep during the week and catch up at the weekend, and it is feared there is a health impact.