We have often heard how important a good night sleep is for the mind. Did you know it can also be important for the waistline?

Adults with late bedtimes and chronic sleep restriction may be more susceptible to weight gain due to the increased consumption of calories during late-night hours.

Those were the findings in a study by researchers at the Perelman School of Medicine at the University of Pennsylvania.

The study was comprised of 225 healthy, non-obese individuals, ranging in age from 22-50 years.  Subjects were randomized to either a sleep restriction or control condition and spent up to 18 consecutive days in the laboratory. Sleep-restricted subjects who spent only four hours in bed from 4 a.m. to 8 a.m. for five consecutive nights gained more weight than control subjects who were in bed for 10 hours each night from 10 p.m. to 8 a.m.

The study found an overall increase in caloric intake during sleep restriction, which was due to an increase in the number of meals consumed during the late-night period of additional wakefulness.  Furthermore, the proportion of calories consumed from fat was higher during late-night hours than at other times of day.

“Although previous epidemiological studies have suggested an association between short sleep duration and weight gain/obesity, we were surprised to observe significant weight gain during an in-laboratory study,” said lead author Andrea Spaeth in a press release. “This late-night eating contributes to weight gain by not only increasing overall daily intake but also by disrupting the timing of caloric intake.”

The study also found that during sleep restriction males gained more weight than females, and African Americans gained more weight than Caucasians.

The recommended number of hours needed for sleep varies as we age. The National Sleep Foundation recommends adults receive 7-9 hours of sleep, while teens should get 8.5 to 9.5 hours. Children 5 to 10-years of age should have at least 10-11 hours and preschoolers need 11-13 hours.