Summary: A new Penn State study shows that when teenagers sleep—their sleep timing—not just how long they sleep, strongly shapes their diet and activity. Tracking 373 adolescents, researchers found that “night owls” (bedtimes after midnight and wake times after 8 a.m.) ate more calories, snacked more often, and spent more time sedentary than peers with earlier schedules.
Importantly, the negative effects of late sleep timing on eating and movement were about twice as strong during the school year, suggesting early school start times that clash with teens’ biological clocks may trigger behaviors that harm cardiovascular health.
Key Facts
- Late-night pattern: Teens who stay up late frequently skip breakfast, rely on high-calorie, carbohydrate-rich snacks, and shift more of their calorie intake to the evening.
- School schedule conflict: The mismatch between adolescents’ natural sleep timing and early school start times amplifies sedentary behavior and poorer eating choices.
- Timing matters: Beyond getting enough hours, sleep timing and regularity have the strongest association with metabolic risk behaviors.
- Sleep as leverage: Researchers suggest stabilizing sleep schedules may be an effective starting point for improving teen diet and physical activity.
Source: Penn State
Overview
When people consider preventing heart disease, diet and exercise usually top the list. This study argues that, especially for adolescents, sleep timing is a foundational influence on both behaviors. The research, published in Sleep Health, examined multiple dimensions of sleep—timing, duration, regularity, and quality—and how each relates to food choices, snacking, and physical activity.
Led by Julio Fernandez-Mendoza at Penn State College of Medicine, the team combined objective measures (wrist actigraphy and in-lab sleep studies) with self-reports to capture a comprehensive picture of adolescent sleep and lifestyle. The goal was to understand whether specific sleep features—beyond total hours—drive differences in eating and activity patterns.
Teens naturally shift to later sleep and wake times during adolescence, yet many school systems require early rising. This biological tendency makes meeting early school schedules difficult and, according to the study, has downstream effects on hunger signals, food cravings, and motivation for physical activity.
“Sleep timing—when teens go to bed and wake up—had the biggest influence on sedentary and eating behavior in teens,” said Fernandez-Mendoza. “Parents and caregivers should protect consistent, earlier bedtimes during adolescence because these routines support healthier eating and movement.”
Study design and participants
The analysis used data from 373 participants in the Penn State Child Cohort (average age 16.4 years; range 12–23). About 63.5% were evaluated while attending school and the rest during school breaks. Researchers tracked bedtime, wake time, total sleep, sleep midpoint and variability, sleep efficiency, and time in bed using actigraphy, polysomnography, and self-report surveys. Diet and snacking were self-reported; physical activity was measured by actigraphy and surveys.
Major findings
- Adolescents with later bedtimes and wake times ate more calories—especially carbohydrates—snacked more often (notably in the evening), and were more sedentary.
- Night owls often skipped breakfast and shifted caloric intake to lunch, dinner, and late-night snacks, which tended to be less nutritious than a standard breakfast.
- Inconsistent sleep duration—alternating between short and long nights—was linked to reduced physical activity.
- These associations were stronger during the school year: when teens had to align with fixed early schedules, the negative effects on diet and sedentary behavior roughly doubled. During breaks, some relationships weakened, although snacking increased for some teens out of school.
The researchers emphasize that sleep is interwoven with eating and activity: circadian timing affects appetite, food choices, and energy to be physically active. Addressing sleep timing and regularity may therefore be a practical strategy to improve adolescent cardiometabolic health.
Practical implications
For caregivers and schools, small changes can help: encouraging earlier, consistent bedtimes, limiting late-night screen time, and reducing late-evening snacking may lower the tendency toward high-calorie nighttime eating and increased sedentarism. Even a modest advance in bedtime—30 minutes—along with stable routines can reduce the clash between a teen’s internal clock and school schedules.
Authors and contributors
Other Penn State co-authors include Kristina Lenker, Susan Calhoun, Jason Liao, Duanping Liao, Edward O. Bixler, and Alexandros N. Vgontzas. Natasha Morales-Ghinaglia and Casandra Nyhuis, both Penn State alumni, also contributed.
Funding: Supported by the National Institutes of Health (Fernandez-Mendoza) and the Fundación Seneca-Science and Technology Agency of Murcia (Ballester-Navarro).
Key Questions Answered
A: Late bedtimes shift the body’s internal clock, disrupting hunger hormones and metabolism. This circadian misalignment increases cravings for quick energy—often carbohydrate- and sugar-rich snacks—during hours the body expects to rest.
Q: Is sleeping in on weekends helpful?
A: Catch-up sleep can reduce short-term tiredness but creates variable sleep duration. The study found that inconsistent sleep patterns are linked to lower physical activity. A steady sleep schedule is more protective for heart health than irregular sleep.
Q: What can parents do if school starts very early?
A: Focus on shifting bedtime earlier, improving sleep regularity, and minimizing late-night blue light exposure. Even small consistent changes can reduce the clash between biological timing and school schedules, lowering the impulse to snack and sit idle.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full.
- Additional context was added by staff.
About this research news
Author: Christine Yu
Source: Penn State
Contact: Christine Yu – Penn State
Image: Credit to Neuroscience News
Original Research: Closed access. “Multidimensional association of sleep health with dietary habits and physical activity in adolescents” by Pura Ballester-Navarro et al., published in 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
Insufficient sleep links to poorer lifestyle choices, but assessing multiple sleep dimensions using both subjective and objective methods offers a fuller view. This study examines how different sleep health dimensions associate with diet and physical activity in adolescents.
Methods
We analyzed 373 adolescents (mean age 16.4 years; 46.6% female) from the Penn State Child Cohort. Sleep was measured via self-report, actigraphy, and polysomnography. Physical activity and METs were measured by actigraphy and self-report; diet was self-reported. Multivariable regression models assessed links between sleep dimensions and lifestyle behaviors.
Results
Later bed and wake times (self-reported and actigraphy) correlated with more snacking, higher calorie and carbohydrate intake, and greater sedentary time. Greater actigraphy-measured sleep variability associated with more sedentarism. Some sleep measures (polysomnography) showed weaker links to lifestyle factors once body mass index was considered.
Conclusions
A multidimensional approach to measuring sleep better captures its relationship with diet and physical activity. Future research should evaluate long-term cardiovascular outcomes linked to these patterns.