Sleep Timing Tied to Development of Excess Fat in Kids

Youth with earlier wake times and sleep midpoints had greater gains in fat mass over 1 year, a researcher reported.

In a convenience sample of non-treatment-seeking young people, ages 8 to 17 years, wake time (P=0.03) and sleep midpoint (P=0.02) were inversely associated with 1-year fat mass, and earlier wake time and midpoint were associated with higher 1-year fat mass, reported Marian Tanofsky-Kraff, PhD, of the Uniformed Services University of the Health Sciences in Bethesda, Maryland, in a presentation at the ObesityWeek virtual meeting. The findings were simultaneously published in Obesity.

However, no other facets of sleep -- weekend catch-up, social jet lag -- was significantly linked with 1-year fat mass (P>0.09), according to Tanofsky-Kraff and colleagues.

"Additional research is needed to determine whether sleep timing may be a modifiable target to prevent pediatric obesity," they stated.

In the study, the average wake time was 7:53 a.m., but ranged from 5:02 a.m. to 11:31 a.m. The average sleep midpoint was 3:46 a.m., but ranged from 1:40 a.m. to 7:26 a.m.

John Dobrowski, MD, of Massachusetts Eye and Ear in Boston, explained to MedPage Today that "earlier wake times and sleep midpoints interfere with metabolic and endocrine recovery and regulation needed in youth for proper metabolism."

Dobrowski, who was not involved in the study, noted that the number of study participants (n=137) was meaningful, but that data from a larger patient population would be useful for verifying the findings.

"All in all, the...information and formulation of opinions are appropriate for the data obtained...[the current study] highlights the importance on sleep and association [with] obesity," he said.

However, Dobrowski pointed out that the study did not "explain the need for shortened sleep, that is, school awakening versus sports activities or even sleep disturbances due to sleep disordered breathing." Studies like the current one "also open further questions [about] calorie consumption in the first hours of awakening or pre-sleep onset due to sleep-onset delays."

And a question that still needs an answer: Which variable -- wake time or sleep midpoint -- is more significant in contributing to obesity? he stated.

"Cooperation with pediatricians, and possibly even schools, to do large-scale data collection with parental approval of sleep times and and awakening, with activity levels during waking hours and calorie consumption, are in order," Dobrowski said. But "for now, emphasis on adequate and good quality sleep without sleep restriction are significant factors in promotion of proper weight, in association with exercise and proper diet," he added.

The research is part of the ongoing, prospective Children's Growth and Behavior Study (started in 2015; estimated to reach completion in 2028) that aims to understand the relationships between eating behaviors and body weight. Other research has made connections between sleep patterns and weight issues for youngsters: A 2021 study in Sleep found that newborns who slept longer and woke up less throughout the night were less likely to be overweight in infancy, while a 2020 study from Italy found that, during the pandemic, time spent in sports activities decreased, while sleep time increased, among children with obesity.

The current study participants wore wrist actigraphy monitors for 14 days. More than half were female with a mean age of 12.5 years. Over a quarter were non-Hispanic Black or African American. Baseline fat mass was 15.3 kg as measured with dual-energy x-ray absorptiometry (DEXA). A little over 28% were overweight or obese at baseline.

Exclusion criteria were a history of brain injury; major medical or psychiatric illness; current pregnancy or history of pregnancy; current and regular use of illicit drugs; >5% body weight reduction during the 3 months prior to screening; or regular use of medications known to impact eating behavior, weight, autonomic functioning, or endocrine functioning.

"Average weekly sleep duration, within-person sleep duration variability, weekend catch-up sleep, bed time and wake time shift, social jet lag, bedtime, wake time, and sleep midpoint were calculated," the researchers explained. "The association of each facet of baseline sleep with 1-year fat mass, adjusting for baseline fat mass and height, was examined."

About a year after completing the screening visits, participants repeated anthropometric measures (fasting weight and height), body composition via DEXA, and physical exam.

The researchers noted that "All data were collected prior to the COVID-19 pandemic."

They also reported that they "did not observe a significant association between social jet lag and fat mass at a 1-year follow- up. Given that, in our sample, mean social jet lag was relatively low (1.1 hours), it is possible that participants were not able to sleep according to their body's circadian preference on the weekends (which would increase social jet lag) because of social demands (e.g., waking early to attend sporting events)."

Study limitations included a relatively small sample size with a broad age range, and not enough youth with overweight or obesity to evaluate how weight status could have impacted the outcomes.

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