Summary: A new study reveals that sleep timing—not just the number of hours slept—is a primary driver of how teenagers eat and move. Researchers followed 373 adolescents and found that “night owls” (those going to bed after midnight and waking after 8 a.m.) consumed more calories, snacked more frequently, and were more sedentary than their early-rising peers.
Crucially, the negative impact of late sleep schedules on diet and exercise was twice as strong during the school year, suggesting that forcing teens to fight their natural biological rhythms to meet early school start times creates a cascading effect on their cardiovascular health.
Key Facts
- The Late-Night Diet: Teens who stayed up late tended to skip breakfast and consume high-calorie, carb-heavy snacks late at night, which are significantly less healthy than typical morning meals.
- The School Conflict: The mismatch between a teen’s natural internal clock and early school schedules significantly worsens sedentary behavior and poor eating habits.
- Beyond Duration: While getting 8–10 hours is important, regularity and timing (when they go to bed) had the biggest influence on metabolic risk factors.
- Sleep as a “Lever”: Scientists argue that fixing sleep routines may be the most effective “entry point” for improving a teen’s overall diet and physical activity levels.
Source: Penn State
When people think about ways to improve cardiovascular health, diet and exercise are often at the top of the list. But long-term health, especially in adolescents, might start with something more fundamental: sleep.
A new study, led by a team from Penn State College of Medicine, found that when teenagers go to sleep and when they wake up may be the driving force behind what teenagers eat and how much they move.
Teens who went to sleep later and woke up later were more likely to consume more calories, snack more and be less physically active — especially when in school compared to on break from school. The findings suggest that sleep could be a lever for protecting heart health, the researchers said.
The study, which was published in the journal Sleep Health, examined how different aspects of sleep — beyond just hours slept — are associated with diet intake and composition, exercise and sedentary behavior in adolescents.
“Sleep is a potential risk factor for cardiometabolic health, even in teens,” said Julio Fernandez-Mendoza, the Edward O. Bixler professor of psychiatry and behavioral health at Penn State College of Medicine and senior author of the study. “Sleep timing — when teens go to bed and wake up — had the biggest influence on sedentary and eating behavior in teens. It’s something parents need to pay attention to — and protect — during critical developmental years like adolescence.”
The body’s internal clock regulates the sleep-wake cycle over 24-hours each day. But it governs other key bodily processes and behaviors too, like metabolism and physical activity. For example, going to bed and waking up late doesn’t just impact a person’s sleep schedule, it also influences their sense of hunger, craving for certain types of food and their desire to move or rest.
“We have the tendency to separate sleep, diet and physical activity as three distinct things, but we can’t isolate them from one another. We have to think about them together,” Fernandez-Mendoza said.
Most adolescents don’t get the eight-to-ten hours of sleep recommended by the National Sleep Foundation. Teens’ internal clocks naturally shift later into the evening during adolescence, which explains why teens may tend to stay up later and sleep in. However, typical school schedules are at odds with teens’ natural drive for sleep. With early school schedules, they need to wake earlier than what their body clock naturally prefers.
Prior studies have found that when adolescents don’t get enough sleep, they tend to be less physically active and to eat poorly, both of which can raise the risk of cardiovascular and metabolic disease. But these studies evaluated sleep based on a single metric, like sleep duration, and self-reported measures, the researchers said. This potentially limits the understanding of the extent of the relationship between sleep, diet and physical activity.
“Sleep is more than just how long a person sleeps but there aren’t many studies that look at this issue from a holistic perspective beyond how much sleep teens get,” said Pura Ballester-Navarro, professor at Universidad Católica San Antonio de Murcia in Spain and first author of the study.
In this study, the researchers wanted to determine if specific aspects of sleep — such as sleep duration, timing, regularity and quality — measured by distinct methods related differently to adolescents’ eating habits and physical activity behaviors, and whether being in school or out of school changes how strong those relationships were.
The study included 373 participants from the Penn State Child Cohort, a longitudinal, population-based study established in 2000. Participants — a mix of males and females — were between the ages of 12 and 23, with an average age of 16.4 years. One set of participants was evaluated while they were in school, and another set was evaluated while they were on break from school.
The researchers monitored multiple aspects of sleep, including bedtime, wake time, total sleep time, sleep midpoint and its irregularity, sleep efficiency and time in bed. They collected data using a combination of objective and subjective methods including wrist-worn wearables, self-report surveys and in-lab sleep studies. They also tracked food intake, snack intake and physical activity.
The team found that adolescents who were “night owls,” generally going to bed after midnight and rising after 8 a.m., consistently ate more calories, particularly carbohydrates, and were more sedentary. They also tended to snack more, especially later in the day and at night.
Because they woke up later, they often skipped breakfast. Instead, they ate lunch, dinner and a late-evening snack, which tended to be less healthy than a typical breakfast. Highly variable sleep duration — when teens alternate nights of shorter and longer amount of sleep — was also associated with less healthy behavior, particularly less physical activity.
The influence of sleep timing and variability on diet and physical activity was two times stronger when school was in session. When teens are forced to sync up with an external schedule and fight their natural biological rhythms, it appeared to have a cascading effect on eating and sedentary behaviors. These relationships seemed to weaken during school breaks, when teens have more flexibility with their schedule. However, increased snacking behavior was observed when kids weren’t in school.
“When the timing of teens’ eating and snacking is out of sync with their normal biological clock, it further dysregulates their sleep,” Fernandez-Mendoza said.
When trying to encourage healthy eating and physical activity, targeting the regularity and timing of adolescents’ sleep could be a key strategy, the researchers said. For example, parents and caregivers can focus on earlier bedtimes, longer sleep duration and consistent sleep schedules during the school year while reducing late-night snacking and sedentary behavior when kids are out of school.
“A consistent sleep routine is a powerful tool,” said Ballester-Navarro.
Other Penn State authors on the paper include Kristina Lenker, assistant professor of psychiatry and behavioral health; Susan Calhoun, associate professor of psychiatry and behavioral health; Jason Liao, professor of public health sciences; Duanping Liao, professor emeritus of public health sciences; Edward O. Bixler, professor emeritus of psychiatry and behavioral health; and Alexandros N. Vgontzas, the Anthony Kales, MD, University Chair in Sleep Disorders Medicine and professor of psychiatry and behavioral health.
Natasha Morales-Ghinaglia, assistant professor of anatomy and embryology at Geisinger Commonwealth School of Medicine, and Casandra Nyhuis, postdoctoral fellow at Johns Hopkins Bloomberg School of Public Health, both of whom earned their doctorates from Penn State, also contributed to the paper.
Funding: Funding from the National Institutes of Health (Fernandez-Mendoza) and the Fundación Seneca-Science and Technology Agency of Murcia (Ballester-Navarro) funded this work.
Key Questions Answered:
A: It’s all about the body’s internal clock. When teens stay up late, their metabolism and hunger hormones get out of sync. This “circadian misalignment” causes the brain to crave quick energy—usually in the form of high-carb, high-sugar snacks—to keep them awake during hours the body thinks it should be resting.
A: Actually, “catch-up sleep” can be a double-edged sword. While it helps reduce immediate exhaustion, the study found that variable sleep duration (switching between short and long nights) is linked to less physical activity. A consistent routine is much more protective for their heart health than a rollercoaster sleep schedule.
A: It’s a tough battle against biology, but the researchers suggest focusing on the “sleep lever.” Helping teens move their bedtime even 30 minutes earlier and reducing late-night blue light can help. The goal is to minimize the “clash” between their natural rhythm and the school bell, which reduces the urge to snack and be sedentary.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurodevelopment research news
Author: Christine Yu
Source: Penn State
Contact: Christine Yu – Penn State
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Multidimensional association of sleep health with dietary habits and physical activity in adolescents” by Pura Ballester-Navarro, Casandra C. Nyhuis, Natasha Morales-Ghinaglia, Kristina P. Lenker, Susan L. Calhoun, Jason Liao, Alexandros N. Vgontzas, Duanping Liao, Edward O. Bixler, and Julio Fernandez-Mendoza. Sleep Health
DOI:10.1016/j.sleh.2026.01.008
Abstract
Multidimensional association of sleep health with dietary habits and physical activity in adolescents
Background
While insufficient sleep is associated with poor lifestyle factors, a multidimensional approach assessing multiple sleep health dimensions via subjective and objective measures has emerged as a more comprehensive method of investigating these relationships. We examine the multidimensional association between sleep health, diet, and physical activity (PA).
Methods
We studied 373 adolescents from the Penn State Child Cohort (16.4 ± 2.3 years; 46.6% female; 20.9% racial/ethnic minority), of whom 234 (63.5%) were evaluated while in-school. Sleep dimensions were assessed via self-reports, actigraphy (ACT), and polysomnography (PSG). PA was assessed via ACT and self-reports, metabolic equivalent of task (MET) via ACT, and diet via self-reports. Stepwise multivariable-adjusted regression models tested the association between sleep dimensions and lifestyle factors.
Results
Later self-reported and ACT-measured bedtime and rising time were associated with more snacking, higher caloric intake, and sedentarism. A later ACT-measured sleep midpoint was associated with higher carbohydrate intake and more snacking. Higher ACT-measured sleep variability was associated with higher sedentarism. Longer self-reported or ACT-measured sleep latency was associated with more snacking and higher PA and METs.
Longer ACT-measured time in bed was associated with lower PA. Sleep dimensions were more strongly associated with diet, PA, and sedentarism among adolescents evaluated while in-school, whereas they were more strongly associated with snacking among those on-break. PSG-measured sleep dimensions were not strongly associated with lifestyle factors; although a greater apnea/hypopnea index was associated with lower METs and greater sedentarism, it was not significant after adjusting for BMI.
Conclusions
Evaluating sleep with a multidimensional approach better captures its association with lifestyle factors. Future research should assess downstream effects on cardiovascular outcomes.
