Good news for folks who enjoy staying in bed on their days off a little longer than they typically do on weekdays: A new study has found that sleeping in on the weekend might help you live longer. Conducted by researchers working out of Stockholm University’s Stress Research Institute in Sweden, the study, which was recently published in the Journal of Sleep Research, flies in the face of conventional sleep wisdom — and to be honest, it's a welcome change. It means that the next time someone tries to shame you for having a lie-in on your day off, you can fire right back at them with proof that it's actually good for you. Isn’t science great?
An oft-cited piece of sleep hygiene advice cautions people against going to bed or waking up at a different time on your days off than you usually do; the argument is that having a regular schedule from which you rarely, if ever, deviate helps your body maintain a certain rhythm, which should then help alleviate any sleeplessness issues you might be experiencing. It’s also long been said that you can’t “catch up” on missed sleep by sleeping later on a different day. However, this latest study seems to suggest that you can actually reap some benefits from sleeping in later on weekends — to a point.
The study used data representing 38,015 people people collected via a survey that was conducted in Sweden in 1997; then, the researchers referred to a national death register to find information about what happened to those people for up to 13 years following the survey. According to the Washington Post, 3,234 of the participants died between 1997 and 2010, largely from cancer and heart disease, giving researchers an average of around six deaths per 1,000 people per year. That’s lower than the world mortality rate for 2010, which was eight deaths per 1,000 people.
Using the survey’s participants’ self-reported sleep duration data, the researchers divided the people into several groups: Short sleepers, who tended to sleep for fewer than five hours per night; medium sleepers, who slept around seven hours per night; and long sleepers, who slept for nine hours or more per night. Then, the groups were subdivided based on how their weekday sleep habits compared with their weekend habits: Short-short sleepers snoozed for fewer than five hours every night consistently throughout the week; short-medium sleepers slept fewer than five hours a night during the week, but seven to eight hours a night on weekends; and long-long sleepers slept at least nine hours every night of the week.
Here’s where it gets interesting: Both short-short sleepers and long-long sleepers had increased mortality rates — but short-medium sleepers didn’t. The results, said lead researcher Torbjörn Akerstedt to WaPo, suggest that “weekend compensation is good” if you miss out on some sleep during the week.
The study seemingly contradicts a different piece of research out of the University of Arizona that was presented at the Annual Meeting of the Associated Professional Sleep Societies in June of 2017. According to this study’s preliminary results, sleeping in on the weekend can actually harm your health — although it’s worth noting that this was only observed to be the case if you stay up much later than your weekday bedtime, then sleep in a ton. The researchers referred to this phenomenon as “social jet lag,” wherein a lack of consistency in bedtimes can impact your sleep quality even if you’re getting the recommended amount of sleep each night.
As Elise Facer-Childs of the University of Birmingham once explained social jet lag to Business Insider, “a lot of our society suffers from social jetlag because we follow a certain schedule during the week for work, and then we follow a different schedule at the weekend because we're either having a lie in or going out for social activities.” If, stated Facer-Childs, you usually wake up for work at 6 a.m., but on your days off, you sleep until 10 a.m., “That’s a four-hour time difference. So for your body, it is like every Friday you jump on a plane and you fly to Dubai, which is a four-hour time zone change, and every Sunday you fly back.”
The point is, all that social jet lag adds up: The University of Arizona researchers found in their study that social jet lag correlated with increased risk of heart disease, bad moods, and general poor health.
At the same time, though, the current study’s results also line up with previous research conducted by the same team. Published in the journal Sleep in July of 2017, this older study examined 14,267 twins from the Swedish Twin Registry and found that those who sleep either less than hours a night or more than eight hours a night had higher rates of mortality —the important point being the total amount of sleep you got each week. Said Akerstedt, who was also the lead researcher for this one, to Business Insider about the results, “It seems like you actually can compensate by catching up on sleep during weekends. This is in effect an argument for lazing around all weekend. There probably is an upper limit, but it's anyway better to increase [sleep hours] on the weekend rather than not doing it at all.”
What’s more, there are other scientifically backed benefits to sleeping in on the weekends: According to a study out of the University of Colorado from 2016, having a lie-in after a week of bad sleep might help stave off diabetes. The study was tiny compared to the others we’ve talked about here — it used just 19 young men as the sample — but the results are worth examining all the same: When the men suffered sleep deprivation for just four nights, their bodies had a harder time handling sugar, according to blood tests — but when they were allowed to get more sleep for the following two nights, their blood test results showed that their systems had already bounced backed.
Of course, the current study is far from the be-all, end-all of sleep length research; indeed, there’s one obvious puzzle still remaining: Exactly why long-long sleepers have mortality rates similar to short-short sleepers. As Diane Lauderdale, professor of epidemiology at the University of Chicago, to the Washington Post, there is “no obvious biological mechanism” that might explain this conundrum — although for his part, Akerstedt told WaPo that he thinks excessive sleeping doesn’t cause harm, but rather indicates that “something else is wrong.” Further research might zero in on this particular area; it might yield some interesting results, indeed.
But in the meantime, the next time someone tells you that sleeping in on the weekend is just going to screw up your sleep even more, go ahead and tell them that you’ve found the Fountain of Youth — and that it looks like the snooze button.