More time in bed benefits morning and evening-type teens differently, new study suggests

A new study has found that teenagers who tend to stay up late and have shorter sleep patterns also experience higher levels of depression, anxiety, irritability, and fatigue than their morning- or intermediate-type peers. The research, published in the Journal of Sleep Research, shows that when these adolescents were allowed an extra hour in bed, both groups increased their total sleep, but evening-type teens delayed their waking times as well, suggesting a unique biological and behavioral response to extended rest.

Teenagers are in a unique position when it comes to sleep. As puberty progresses, the body’s internal clock tends to shift later, making it harder for many adolescents to fall asleep early despite early morning school start times. At the same time, academic and social demands can further reduce the total amount of rest teens get. Chronic short sleep has long been associated with struggles in mood, behavior, and daily functioning. The researchers wanted to understand if adolescents with different internal clock patterns responded differently when given a chance to extend their time in bed.

“My research is focused on adolescent sleep health and the association of sleep with physical and mental health in teens,” said study author Stacey L. Simon, an associate professorat the University of Colorado Anschutz Medical Campus and associate director of behavioral sleep medicine at Children’s Hospital Colorado.

“We know that the majority of adolescents obtain less than the recommended amount of sleep for their age, and tend to go to bed late despite needing to wake early for school. Not getting enough sleep can have significant impacts on academic, social, and emotional functioning, and increase risk for health problems. This study examined how teens with different sleep timing preferences (morning vs evening preferences) responded to a sleep extension intervention where we helped them to get more sleep for one week.”

For their study, the researchers recruited 26 high school students between the ages of 14 and 19 who were sleeping an average of seven hours or fewer on school nights. The volunteers were recruited through school and social media ads and screened thoroughly to ensure they were otherwise healthy, did not have psychiatric or sleep disorders, and were not using medications that affect sleep.

The participants came from a range of racial and ethnic backgrounds, and the sample was primarily female. The researchers classified each adolescent as a morning, intermediate, or evening type using a standard questionnaire about their sleep habits and daily activity patterns.

Each adolescent participated in a randomized, crossover design experiment. In one condition, they kept to their usual school-week routine, called “typical sleep,” and in the other condition, called “sleep extension,” they increased their time in bed by at least an hour each night for five nights. The order of these conditions was randomized, and a one-month washout period was used between conditions.

During both conditions, participants wore a wrist device called an actigraph that tracked their activity and estimated their sleep, kept a diary of their sleep habits, and came into the lab at the end of the study period for more detailed measurement of their internal biological clock.

In the lab, participants stayed in a dimly lit room and gave hourly saliva samples throughout the evening and the following morning. These samples were used to measure melatonin, a hormone that signals the body to prepare for sleep. By doing this, researchers were able to pinpoint the participants’ “dim light melatonin onset” and “dim light melatonin offset” — times when the body naturally ramps up and down its release of the hormone — providing a biological marker of each person’s internal clock.

At the start of the study, the researchers found significant differences between evening-type adolescents and those classified as morning or intermediate types. The evening types had higher scores for depression and anxiety and were more irritable and sleepy throughout the day. They also experienced more symptoms related to chronic lack of sleep.

When the participants increased their time in bed, both morning/intermediate and evening types were able to advance their bedtimes and sleep longer. However, only evening-type participants delayed their wake times in the extended-sleep condition. In other words, while both groups adjusted when they fell asleep, only evening types also adjusted when they woke up, indicating that their internal biological clock played a strong role in their ability to sleep longer.

The researchers also looked closely at changes in the biological markers associated with the body’s internal clock. The phase angle — or the interval between when the body began producing melatonin and when a person fell asleep — narrowed significantly for morning and intermediate types when they went to bed earlier. Meanwhile, the interval between when evening types stopped producing melatonin and when they woke up increased significantly when their time in bed was extended.

This suggests that evening types may have a harder time aligning their internal biological clock with an earlier waking time, making it more challenging for them to maintain a longer sleep duration when their alarm goes off early.

This finding adds an important piece to the puzzle of adolescent sleep health. The results point to the benefit of considering an adolescent’s natural sleep tendency when making recommendations for increasing rest and aligning circadian rhythms. Evening-type adolescents may require different approaches, such as focusing more on later wake times or using targeted interventions to shift their internal clock earlier.

“All teens in the study were successful at increasing their sleep duration with the intervention,” Simon told PsyPost. “They all shifted their bedtimes earlier to achieve additional sleep. However only the adolescents with an evening preference also delayed their wake time in the morning as a way to get additional sleep. This suggests that individualized approaches may be needed to help adolescents improve their sleep.”

The study has some limitations. The sample was relatively small and largely homogenous, making it challenging to generalize the results to all adolescent populations. The one-week experimental period also may not fully capture how longer or more sustained changes in sleep behavior affect adolescents with differing internal clock patterns. The researchers acknowledge the need for larger, longer studies that could also investigate how extending sleep impacts academic performance, emotional well‑being, and long‑term health.

The study, “Evening Chronotype Is Associated With Daytime Impairment and Differential Sleep and Circadian Response to a Sleep Extension Manipulation in Short Sleeping Adolescents,” was authored by Stacey L. Simon, Emily Cooper, Angel Bernard, Anne E. Bowen, Sydney Holtman, John T. Brinton, Stephen M. M. Hawkins, Melanie G. Cree, Kristen J. Nadeau, and Kenneth P. Wright Jr.