New US research has found that going to bed late at night and not keeping a regular sleep schedule appears to be associated with a greater risk of obesity in teenage girls.
Led by researchers at Massachusetts General Hospital for Children (MGHfC) and Harvard Medical School, the new study looked at 418 girls and 386 boys aged 12 to 17 and asked them to wear a wrist actigraph -- which records periods of rest and activity -- for five days or more.
The researchers used the data to examine each participant's chronotype, which is their preference for staying up late in the evening versus getting up early in the morning, and "social jet lag," which is the difference in sleep timing between school and free days.
The participants were also asked to complete questionnaires, and researchers recorded their anthropometric measurements, which are measurements of the muscle, bone, and adipose tissue used to assess the composition of the body.
The findings, published in JAMA Pediatrics, showed that an evening chronotype and greater social jet lag were associated with a greater likelihood of being overweight in girls, but not in boys.
For the girls, staying up later was associated with an average .58 cm increase in waist size and a .16 kg/m2 increase in body fat, and each hour of social jet lag was associated with a 1.19 cm larger waist size and a 0.45 kg/m2 increase in body fat.
The findings also held true even after taking into account sleep duration and other lifestyle behaviors.
"Beyond quantity and quality, timing is a vital component of sleep because it determines if an individual's circadian clock -- the internal sleep/wake schedule -- is synchronized with the rhythms of their daily activities," said Elsie Taveras, MD, MPH, senior investigator. "This is particularly important to adolescents whose evening preferences and academic demands often result in irregular sleep schedules that may cause circadian misalignment."
The researchers say the findings emphasize the need for teens to keep a consistent sleep-wake patterns throughout the week, including on weekends.
"Large variability in sleep patterns across the week can disrupt normal physiology, resulting in obesity and cardiometabolic risk," explained lead author Elizabeth Cespedes Feliciano, ScD, ScM. "Our study supports the importance of biological clocks in influencing obesity risk."
"Families should encourage consistency in their children's sleep schedules and their bed and wake times as well as improvements in their sleep hygiene by limiting electronic media and caffeine use in the evening," said Feliciano.