During adolescence, young people naturally begin to fall asleep later and often struggle to adjust their circadian rhythm to the school timetable. Combined with catching up on sleep at weekends and using social media late at night, this can lead to a phenomenon known as social jet lag. Its consequences are wide-ranging, from an increased risk of depression and impaired concentration to a greater tendency to reach for unhealthy snacks.
“Circadian rhythm disruption occurs when the body is not regularly exposed to sufficiently strong light. As a result, the mechanisms encoded in our genetic material—known as clock genes, which operate in an oscillating cycle lasting slightly more than 24 hours—are not synchronised with the external world,” Dr Iwona Piątkowska, a biomedical specialist with a doctorate in physical culture sciences, dietitian and wellbeing expert, told the Newseria news agency.
“The most important thing is to expose ourselves to a large amount of daylight relatively soon after waking up, because this is the strongest signal telling our endogenous circadian rhythms that a new day has begun,” she added.
As the expert explains, the body’s master biological clock is located in the brain, but endogenous circadian rhythms affect every organ, tissue and bodily function. They influence, among other things, insulin sensitivity, alertness, memory, perception and concentration.
“Our internal organs have their own circadian rhythms. One could even argue that there are no two minutes during the day when the body functions in exactly the same way. This is linked to evolution. When we consider the conditions in which humans developed as a species, the only certainty was that darkness would be followed by light, and light by darkness,” Dr Piątkowska said.
“We would like all our organs to be synchronised with periods of light and darkness, but today’s lifestyle does not support this,” she added.
The consequences of a disrupted circadian rhythm can be serious and multidimensional. According to the expert, they may include poorer memory, low mood, an increased risk of depressive symptoms, panic attacks and anxiety.
“On the one hand, our functioning is influenced by our genes. We can distinguish five chronotypes, ranging from extremely early larks to extremely late owls. On the other hand, we also have social clocks. We often cannot change the time at which we start work, let alone the time at which school begins,” she said.
“Light is another factor. When we do not receive enough of it during the first few hours after waking, we gradually feel the need to get up later and later,” she explained.
Circadian rhythms become disrupted when people go to bed and wake up at different times each day. Another important factor is the mismatch between an individual’s preferred times for sleeping, waking and being active and the demands imposed by society.
This is particularly evident among teenagers, for whom circadian disruption is extremely common. One of the main reasons is social jet lag, defined as the difference between the midpoint of sleep on weekdays and at weekends. The body then functions somewhat as though it were regularly travelling between different time zones.
“If a young person goes to bed at 11 p.m. and gets up at 6 a.m. during the week, the midpoint of their sleep falls at 2:30 a.m. If they sleep from midnight until 10 a.m. at the weekend, the midpoint is 5 a.m. That difference is social jet lag,” Dr Piątkowska explained.
“This phenomenon is particularly visible among young people because adolescence is associated with a natural shift in chronotype towards that of a so-called night owl. In other words, the pressure to sleep appears later,” she added.
According to the National Sleep Foundation, school-age children should sleep between nine and 11 hours a night, while teenagers require between eight and 10 hours. However, good physical and mental health depends not only on getting enough sleep, but also on maintaining a regular sleep cycle.
Circadian rhythm disturbances among teenagers are caused not only by natural biological processes during puberty, which delay the time at which they become sleepy, but also by the need to adjust to early school schedules.
At weekends, the absence of a school timetable allows young people to regulate their own sleeping hours. The expert also points to unrestricted access to social media. The perceived need to remain constantly active online encourages teenagers to delay going to sleep.
“A significant part of teenagers’ lives takes place on social media, which is accessible 24 hours a day, unfortunately including late at night, when a young person’s body should have been asleep for a long time,” the dietitian said during a conference organised by the Warsaw Academy of Medical and Technical Applied Sciences.
Social Jet Lag May Increase the Risk of Depression
A meta-analysis published in 2025 in the journal BMC Psychiatry found that social jet lag of at least two hours was associated with a 44% higher risk of depressive symptoms among adolescents compared with lower levels of social jet lag.
Research conducted by scientists from Penn State College of Medicine and published in the journal Sleep Health also found that insufficient and irregular sleep among a group of nearly 400 teenagers was associated with lower levels of physical activity, higher consumption of sugary and high-fat foods, and a failure to maintain regular mealtimes.
“Increased appetite is connected with the fact that, when we are sleep-deprived, the areas of the brain responsible for hedonistic behaviour become more active. Sleep deprivation is also associated with lower concentrations of satiety hormones and higher levels of ghrelin,” Dr Piątkowska explained.
Similar conclusions were drawn from a cross-sectional study published in Chronobiology International. Researchers from the University of Oxford analysed the sleep habits of approximately 20,000 students aged between nine and 18.
Almost all of them—99.8%—showed a discrepancy between their sleeping and waking times on school days and at weekends. Average social jet lag was close to two hours and was correlated with age. It increased until the age of 15, when it reached a peak of two hours and seven minutes.
The researchers also confirmed that greater social jet lag was associated with using social media and playing video games during the hour before bedtime.
The study additionally highlighted the beneficial role of parents or other family members in setting weekend bedtimes, which may help reduce social jet lag among children and adolescents.
“The first step is education and explaining how important it is to go to bed and wake up at regular times and to protect the circadian rhythm. The parents of an individual teenager should be educated, but so should all parents within that young person’s social group,” the expert argued.
“Even when a parent understands the problem and insists that their teenage child should not use a smartphone under the covers, if the teenager’s closest friends have different habits, this may simply create more stress and a greater sense of the well-known FOMO—fear of missing out,” she said.
“With better education on this subject, the gap between the time when a young person should be sleeping and recovering and the behaviour demanded by their social ecosystem could perhaps be reduced,” she added.
Could Schools Start Later?
Another possible solution would be to move the beginning of the school day to a later hour.
Recognising that early school start times negatively affect young people’s physical and mental health and make learning more difficult, the American Academy of Sleep Medicine recommends that classes should begin no earlier than 8:30 a.m. Such policies have already been introduced in some US states.
“If I lived in an ideal world, I would say that the first thing we should do is adapt the education system to young people rather than to teachers. However, I know that this is not going to happen,” Dr Piątkowska said.
“Moreover, the consequences of such changes, including those introduced in California, have not been entirely positive, mainly because of logistical difficulties. For that reason, this solution is probably more of an idealistic vision than a realistic option,” she concluded.
