Teen bedtime may be key factor in diet, activity patterns

In an effort to combat cardiometabolic health risks and weight-related behaviors, health experts have traditionally focused on two main pillars: diet and exercise. However, new research from the Penn State College of Medicine suggests that we may be overlooking a more fundamental component.

The specific timing of a teenager’s sleep-wake cycle may be one of the strongest behavioral factors influencing adolescents’ eating and activity patterns, according to the results of a recent study published in Sleep Health.

To study this, a team of researchers, including the senior author Julio Fernandez-Mendoza, Ph.D., a psychiatry and behavioral health professor at the Penn State College of Medicine, gathered data from 373 patients using the Penn State Child Cohort. Participants, who were an average of 16 years old, were separated into two groups: those in school and those on a school break.

The study revealed that adolescents who go to bed after midnight and wake up after 8:00 am are significantly more likely to engage in unhealthy habits than teenagers who go to sleep and rise earlier. Specifically, later sleep timing was associated with increased calorie consumption, higher intake of fats and carbohydrates and more frequent snacking, particularly in the afternoon and evening.

The study also revealed that the link between late sleep timing and unhealthy behavior was twice as strong during the school year.

“Having to adapt to morning school schedules and extracurricular activities, combined with the challenges adolescents face in achieving adequate sleep, may influence the strength of association with health behaviors: while on-break, there may be greater flexibility, which may weaken these associations,” Fernandez-Mendoza said in the study.

Biological changes that occur during puberty can alter the circadian rhythm, which controls the body’s sleep-wake cycle, and is likely the reason that adolescents go to bed late. Although this typically stabilizes in adulthood, it is a problem for teenagers because of their early school schedules and academic pressure.

When someone’s circadian rhythm is at war with external events, such as early school start times, a phenomenon called “social jetlag” occurs.

When school schedules force "night owls" to wake up early, the resulting exhaustion is also linked to increased sedentary behavior. Instead of being physically active, tired teens spend more time sitting, often fueled by the high-carb snacks their bodies crave for quick energy.

With approximately one-fifth of children and adolescents in the United States currently considered obese, the importance of sleep timing cannot be overstated.

“Finally, the current findings reinforce the critical importance of using objective sleep measures in clinical assessments, particularly at-home actigraphy, when studying the relationship between sleep and health behaviors in adolescents,” Fernandez-Mendoza said.

The study’s findings also suggest that improving a teen's health might start with stabilizing their internal clock.

“During the school term, when adolescents follow stricter schedules, interventions should focus on advancing bedtime, increasing sleep duration and reducing variability, as these factors were most strongly linked to high-calorie diets and sedentarism,” Fernandez-Mendoza said. “In contrast, during school breaks, interventions might more effectively target delayed sleep timing, late-night snacking and declines in physical activity.”