People who slept in on weekends after short weekday nights died at the same rate as steady sleepers

Many working adults run their sleep on a weekly cycle: five short nights, then two long ones. Whether the long nights make up for the short ones is one of the most practical questions in sleep research, and for years it went almost unasked. Studies of sleep and health mostly recorded a single figure for how long a person usually slept, and that figure reflected the working week.

In 2018 a Swedish team reported a result that seemed to answer the question in favor of the lie-in. People who slept little on weekdays and longer on weekends died at the same rate as people who slept a steady six or seven hours. It was reported as good news for the weekend lie-in. Studies published since then make that reading hard to sustain.

What the Swedish study of weekend sleep measured

The data came from the Swedish National March Cohort, recruited in September 1997 at a fundraising event for the Swedish Cancer Society held at 3,600 sites throughout Sweden. A total of 43,880 people returned a 36-page questionnaire about their lifestyle and medical history. After exclusions, mostly for missing answers, the analysis covered 38,015 adults.

Two questions made the study unusual. One asked how many hours people usually slept on a workday or weekday night, and the other how many hours they slept per night on days off. Torbjörn Åkerstedt of Karolinska Institutet, who led the analysis, later explained the reason to a reporter: earlier research had asked only about typical sleep, and Åkerstedt told Popular Science that previous work had not considered weekend sleep separately.

The participants were then followed through the national death register from October 1997 to the end of 2010. Up to the end of that period, 3,234 deaths occurred.

What the study found about short weekday nights and weekend sleep

The patterns appeared only in people under 65, the usual retirement age in Sweden.

Looking at weekends alone, those who slept five hours or less on their days off had a death rate 52% higher than those who slept seven. Long weekend sleep, nine hours or more, carried no extra risk. That is itself a departure from earlier work, which had tied long sleep as well as short sleep to higher mortality.

The more revealing analysis combined the two answers.

Sleep pattern in adults under 65	Death rate compared with a steady 6 to 7 hours
Five hours or less on weekdays and weekends	65% higher
Eight hours or more on weekdays and weekends	25% higher
Short on weekdays, medium or long on weekends	No difference

The authors put the central result this way: the mortality rate among participants with short sleep during weekdays, but long sleep during weekends, did not differ from the rate of the reference group. Among those aged 65 or over, sleep duration showed no relationship with mortality at all. In that age group the gap between weekday and weekend sleep had almost closed, because the discrepancy between the number of hours slept per night during the week and on days off decreased as age increased.

Two ways to read the weekend catch-up sleep result

Åkerstedt and colleagues offered the hopeful interpretation, that short weekday sleep may be compensated for during the weekend. They also offered a second, and said they could not choose between them.

The alternative is that a long weekend sleep is a sign of health and not a remedy. A person who sleeps longer when the alarm is switched off has a sleep system that responds normally to the chance of more rest. A person who sleeps five hours even on a free morning may be a different kind of sleeper, for reasons the questionnaire did not capture. On this reading the lie-in marks the healthier group without doing anything for them.

The paper is direct about its inability to settle the matter. Sleep was reported once, in 1997, and never again. “With the present approach, with merely one measure of sleep at baseline, we cannot be sure that longer weekend sleep is a true compensation,” the authors wrote. They describe the compensation idea as speculative, and note that too few people fell into the short-weekday, long-weekend group to separate medium from long weekend sleep. Åkerstedt gave the same warning in an interview, saying that this is not an experimental study.

What a sleep laboratory trial of weekend recovery found

An experiment was published the following year. Christopher Depner and colleagues at the University of Colorado Boulder brought 36 healthy young adults into a laboratory, where they were randomly assigned to one of three groups. Eight had nine hours in bed every night. Fourteen were held to five hours a night throughout. The remaining fourteen had five hours a night for a simulated workweek, then a weekend in which they could sleep as much as they chose, then two more short nights.

The weekend did not come close to repaying the loss. Participants slept about three hours more than usual across Friday and Saturday nights, then slept less than usual on Sunday night, when they chose their own bedtime before an early start. Over the whole weekend they slept only about 1.1 hours more than their estimated total sleep need, against more than twelve hours of sleep lost during the workweek.

The measurements that followed showed no protection. Short sleep increased eating after dinner and body weight in both groups. During the free weekend the after-dinner eating eased, and when short nights resumed it returned, along with the weight gain. Sensitivity to insulin, the hormone that clears sugar from the blood, fell by about 13% in the group with continuous short sleep and by roughly 9% to 27%, depending on the tissue measured, in the weekend recovery group. The body clock in that group had also shifted later.

The authors concluded that weekend recovery sleep is not an effective strategy to prevent the metabolic effects of repeated short sleep. The trial was small and short, its volunteers were young and healthy, and it measured metabolism over days, a long way from deaths over years.

What studies with measured weekend catch-up sleep show

Self-reported sleep is unreliable, so the most direct check on the Swedish result is a study in which sleep was recorded by a device. Jean-Philippe Chaput and colleagues did this in a prospective cohort study of UK adults who wore wrist-attached accelerometers, which are motion sensors. It included 73,513 people in the analysis of deaths and 70,518 in the analysis of heart disease, followed for an average of eight years.

They found nothing. Weekend catch-up sleep was not associated with mortality or with new cardiovascular disease, and that held among people who slept less than six hours on weekdays, the group that would be expected to gain the most. The authors noted the conflict with earlier advice: “These findings do not align with previous evidence and recommendations by sleep authorities suggesting that extending sleep over the weekend may offer protective health benefits.”

Two other studies complicate the picture without resolving it. Takuya Yoshiike and colleagues in Japan analyzed 3,128 middle-aged participants in the US Sleep Heart Health Study, whose sleep had also been recorded overnight with monitoring equipment. A modest catch-up of about an hour went with lower mortality in people whose measured sleep was normal, and with higher mortality in people whose measured sleep was very short. Their conclusion was that sufficient sleep may reduce weekday sleep debt and only a short catch-up would then be required. An analysis of a US health survey by Hong Zhu and colleagues found that catch-up sleep of more than two hours is strongly associated with reduced cardiovascular disease prevalence when the sleep duration is under six hours on weekdays. That study measured everything at a single point in time, so it cannot show which came first.

Sleep regularity and the cost of a long weekend lie-in

A different line of research suggests the lie-in has a price. Daniel Windred of Monash University and colleagues studied sleep regularity, the day-to-day consistency of sleep-wake timing, in 60,977 UK adults with sensor recordings. Sleep regularity was a stronger predictor of death from any cause than sleep duration was. The people in the four more regular fifths had a risk of death 20% to 48% lower than the least regular fifth.

A two-hour lie-in on Saturday and Sunday is, by definition, irregular sleep. It may be part of the reason the Colorado volunteers slept less on Sunday night and started the next week with a body clock running late.

Expert opinion tries to hold both results together. A National Sleep Foundation panel that reviewed 63 publications in 2023 agreed that regular timing matters: “Consistency of sleep onset and offset timing is important for health, safety, and performance.” The panel also agreed that when insufficient sleep is obtained during the week, catch-up sleep on days off may be beneficial. Chaput’s device-based study, published a year later, was in part a test of that second statement, and did not support it.

Why the weekend catch-up sleep studies disagree

No study has randomly assigned people to years of weekend lie-ins and counted deaths, and none is likely to. The evidence is therefore a short experiment with metabolic outcomes and a set of observational studies that disagree.

The disagreement has identifiable sources. The Swedish study relied on one answer to a questionnaire. Sensor studies rest on short recordings: in the UK data analyzed by Windred, participants wore accelerometer devices for 1 week. Both are snapshots of habits that change. The Swedish authors point out that one should expect a reduction in weekend sleep as people age, so the 1997 answers describe the following thirteen years imperfectly. Neither design can separate people who choose to sleep in from people who are able to.

Short sleep on every night of the week was linked to higher mortality in the Swedish data, and nothing in the later research contradicts that. What remains unsettled is whether two long mornings undo five short nights or merely show that the sleeper is otherwise well.

People who slept longer on weekends after short weekday nights lived as long as steady sleepers in one large study, though a laboratory trial and a study with wrist sensors found no clear protection, so whether a lie-in repairs a short week has not been shown.