The long-standing advice with sleep is that consistency is key. If you have a late night here and there, and you sleep in occasionally, it's usually fine if you tend to stick to a routine.
People often sleep in at the weekends to try and "catch up" on missed sleep. But according to a new study, this doesn't really work.
The research, published in the journal Current Biology, was conducted at the University of Colorado, Boulder. The results found that while sleeping in may make you feel better in the moment, trying to catch up and then returning to poor sleep habits in the week can make things worse for your routine and possibly for your health, too.
"Our findings suggest that the common behavior of burning the candle during the week and trying to make up for it on the weekend is not an effective health strategy," said author Kenneth Wright, a professor of integrative physiology and director of the Sleep and Chronobiology Lab.
The team recruited 36 volunteers, aged 18 to 39, to stay at the Clinical Translational Research Center at the Anschutz Medical Campus for two weeks so their eating, light exposure, and sleep could be monitored.
They were divided into three groups: one group had nine hours sleep a night, the second had five hours per night, while the third group had five hours for five days then were allowed to sleep in as much as they liked for two days - like a weekend - before returning to five hour nights for the remainder of their stay.
The groups who had restricted sleep snacked more at night, gained weight, and saw declines in insulin sensitivity - the hormone that helps our body regulate sugar levels. The "weekend" group saw mild improvements, but the effects didn't last.
In fact, the weekend group actually came out worse for insulin sensitivity, which declined by 9 to 27%, and was worse in the muscles and liver than the other groups. Severely reduced insulin sensitivy over time can lead to the development of diabetes.
"It could be that the yo-yoing back and forth - changing the time we eat, changing our circadian clock, and then going back to insufficient sleep is uniquely disruptive," said Wright.
It's hard to get enough sleep during the week, especially if you're a night owl and you have a 9 to 5 job. But research has consistently shown that the best thing for you is to stick to a bedtime, and try and wake up at the same time every day.
However, last year, a couple of studies suggested there were benefits to sleeping in at the weekend. One published in the journal Sleep looked at the sleeping habits and overall health of 43,000 people and found that those who slept less than five hours a night, or more than 8 hours a night, had much higher rates of mortality than those who slept more. Overall, it was the average amount of sleep somebody got that seemed to make a difference.
At the time, Torbjörn Åkerstedt, a biological psychology professor at the Center for Stress Research at Stockholm University and lead author of the study, said: "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."
A follow-up study using the same data found that adults under age 65 who got only five hours of sleep or less a night, for seven days a week, had a higher risk of early death than those who consistently got six or seven hours. But those who made up for it at the weekend by sleeping in had no raised mortality risk compared with the steady sleepers.
"The results imply that short (weekday) sleep is not a risk factor for mortality if it is combined with a medium or long weekend sleep," said Åkerstedt. "This suggests that short weekday sleep may be compensated for during the weekend, and that this has implications for mortality."
Overall, sleep researchers generally agree that the best way to sleep is consistently, and while sleeping in is sometimes fine, there's no substitute for getting enough hours every night.
In the new study, people in the weekend group recovered slightly after sleeping in, but then found it harder to fall asleep Sunday night, making it even harder to get up on Monday morning
Wright said there may be some value in sleeping in for people who occasionally have a late night, but more research needs to be done to know how beneficial it could be.