Going to sleep late in their teens and adulthood may be making people fatter / Hulton Archive/Getty Images

A study has found a link between sleeping later during the working week and an increase in body mass index

Going to bed late could be making people fatter, according to a new study.

Research published in the American journal Sleep this month suggests that going to bed later during the working week, as a teenager through to adulthood, is linked to an increase in body mass index over time.

A summary of the report said: “The aim of the current study was to examine the longitudinal relationship between bedtimes and body mass index (BMI) from adolescence to adulthood in a nationally representative sample.

“The results highlight bedtimes as a potential target for weight management during adolescence and during the transition to adulthood.

"Later average bedtime during the work week, in hours, from adolescence to adulthood, was associated with an increase in BMI over time.

"These results remained significant after controlling for demographic characteristics and baseline BMI.

“Although sleep duration, screen time and exercise frequency did not attenuate the relationship between work day bedtime and BMI over time, fast food consumption was recognised as a significant partial mediator of the relationship between bedtimes and BMI longitudinally.”

The research was carried out by academics at the University of California Berkeley, Columbia University and the New York Psychiatric Institute, and assessed the bedtimes of 3,300 teenagers between 1994 and 2009.

Earlier this year, Public Health England encouraged people to sleep more in a government campaign to promote healthier lifestyles.

“Lack of sleep is a growing problem,” according to Lisa Artis, of the British Sleep Council.

“Firstly people don’t place enough importance on sleep and the health benefits being well-rested can have.

“Secondly, unlike a lot of well understood life changes such as eating five portions of fruit and vegetables a day, sleep isn’t really on the agenda.”

Research has also suggested that routinely getting less than six hours sleep a night can impact attention, concentration and memory, and is linked to Alzheimer’s disease.