The short and long of adolescent sleep: the unique impact of day length

Bidirectional association between light exposure and sleep in adolescents

Sleep behaviour is controlled by both circadian and homeostatic influences. Changes in both factors are related to the delayed sleep timing observed in adolescence, which also generates restrictions in their sleep duration. In addition, the circadian factor explains part of the observed influence of light on sleep duration. We recorded 15 high-school students for 23 days (vacation: 11 days; school term: 12 days) using GENEactive accelerometers. We employed a repeated-measures analysis to explore the day-to-day bidirectional association between mean light exposure and sleep behaviour across a period with extreme variability in social pressures. Sleep onset was more than 30 min earlier and sleep duration almost 20 min longer when previous day light was 10 times more intense. Light intensity had a reduction of more than 20% as sleep ended 1 hr later. Besides, sleep onset and offset were both later during vacation than on school days (almost 2 hr and 4 hr, respectively) and free days (almost 1 hr, respectively). Therefore, sleep duration was almost 2 hr longer on vacation and free days than on school days. On the other hand, light exposure intensity was twice as high during vacation days when adjusted by sleep timing. Insufficient sleep duration is a major problem for adolescents. Although we found that light exposure was associated with longer sleep duration, the influence of school start times was greater and ended up prevailing, which explained the short sleep durations observed on school days.

How Are Adolescents Sleeping? Adolescent Sleep Patterns and Sociodemographic Differences in 24 European and North American Countries

PURPOSE

Insufficient and poor sleep patterns are common among adolescents worldwide. Up to now, the evidence on adolescent sleep has been mostly informed by country-specific studies that used different measures and age groups, making direct comparisons difficult. Cross-national data on adolescent sleep that could inform nations and international discussions are lacking. We examined the sleep patterns of adolescents across 24 countries and by gender, age, and affluence groups.

METHODS

We obtained sleep data on 165,793 adolescents (mean age 13.5 years; 50.5% girls) in 24 European and North American countries from the recent cross-sectional Health Behaviour in School-aged Children surveys (2013-2014 and 2017-2018). For each country, we calculated the age-standardized mean in sleep duration, timing, and consistency and the proportions meeting sleep recommendations on school and nonschool days from self-reported bedtimes and wake times. We conducted stratified analyses by gender, age, and family affluence group.

RESULTS

Adolescent sleep patterns varied cross-nationally. The average sleep duration ranged between 7:47 and 9:07 hours on school days and between 9:31 and 10:22 hours on nonschool days, and the proportion of adolescents meeting sleep recommendations ranged between 32% and 86% on school days and between 79% and 92% on nonschool days. Sleep patterns by gender and affluence groups were largely similar, but older adolescents slept less and went to bed later on school days than younger adolescents in all countries.

CONCLUSIONS

The sleep patterns of adolescents vary across countries and sociodemographic groups. Insufficient sleep on school days is common in many countries. Public health and policy efforts to promote healthy adolescent sleep are encouraged.

Preventing sleep deficit in adolescents: Long-term effects of a quasi-experimental school-based intervention study

Adolescents are at risk of sleep deficit, which has serious consequences for their daytime functioning. However, school‐based interventions to improve sleep have shown limited success. This might be due to the content of the programmes (e.g., not targeting central factors such as daytime stress and technology use) or because changes have not been captured due to a lack of long‐term follow‐ups. Hence, the aim of this study was to evaluate the long‐term effects of a school‐based sleep education curriculum including time‐management training. The study used a quasi‐experimental design. Participants were 3,622 adolescents (mean age 13.7, 48% girls); 286 were in the intervention group and 3,336 were followed as a natural control group. Data were collected before the intervention and at a 1‐year follow‐up. We divided participants into three groups according to baseline sleep duration (calculated from self‐reported bed‐ and wake times, minus sleep onset latency): insufficient (<7 hr), borderline (7–8 hr) and adequate (>8 hr). Adolescents in the intervention group were ~2 times less likely to report insufficient sleep at follow‐up as compared to controls. Sleep knowledge improved significantly in the intervention group but there were no changes in emotional sleep hygiene (e.g., bedtime worry) and perceived stress. Surprisingly, technology use increased and behavioural sleep hygiene worsened in the intervention group. Although the mechanisms of change need further investigation, the results of this study point to potential long‐term benefits of school‐based sleep programmes.

Using big data to explore worldwide trends in objective sleep in the transition to adulthood

BACKGROUND

Development induces changes in sleep, and its duration has been reported to change as a function of aging. Additionally, sleep timing is a marker of pubertal maturation, where during adolescence, the circadian rhythm shifts later. Typically, this is manifested in a later sleep onset in the evening and later awakening in the morning. These changes across development seem to be universal around the world but are unlikely to persist into adulthood.

METHODS

This study utilized accelerometer data from 17,355 participants aged 16-30 years (56% female) measured by validated Polar wearables over a 14-day period. We compared sleep duration, chronotype (sleep midpoint) and weekend catch-up (ie, social jetlag) sleep across ages and regions over 242,948 nights.

RESULTS

The data indicate a decline in sleep duration as well as a dramatic shift in sleep onset times throughout adolescence. This continues well into early adulthood and stabilizes nearer age 30. Differences in sleep duration across ages were significant, and ranged from 7:53 h at age 16 to 7:29 h at age 30 in the sample. Additionally, there was a clear difference between females and males throughout adolescence and young adulthood: girls had longer sleep duration and earlier timed sleep in the current study. Differences in sleep were found between regions across the world, and across European areas.

CONCLUSIONS

Both sleep duration and sleep timing go through a clear developmental pattern, particularly in early adulthood. Females had an earlier sleep midpoint and obtained more sleep. Regional differences in sleep occurred across the world.