Analysis showed that those aged 65 or under who slept five hours or less each day had a 25% higher risk of early death than those who had six to seven hours of sleep.
"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 the researchers, led by Torbjorn Akerstedt. A study of Korean adolescents found that those who sleep in on the weekends to make up for a busy week actually have a higher risk of self-injury and suicidal thoughts, as noted by Popular Science, while current research also indicates that you can't make up for the cognitive decline brought on by nights with little shut-eye.
The magic number? Eight or more hours of sleep on weekends is what you'll need if you plan to catchup on those lost hours from averaging five hours or less during the week.
"Sleep duration is important for longevity", said Torbjörn Åkerstedt, first author of the study, at the Stress Research Institute, Stockholm University, and Karolinska Institute, also in the Swedish capital.
Researchers in Sweden followed 38,000 people for 13 years, starting in 1997.
"I suspected there might be some modification if you included also weekend sleep, or day-off sleep", he said, adding: "The assumption in this is that weekend sleep is a catch-up sleep".
Having said that, the study also found that it is possible to catch up on sleep with an extended lie-in in the weekend, reports the Guardian.
And Michael Grandner, who heads the University of Arizona's Sleep and Health Research Program, told The Washington Post that it's wrong to believe a long sleep on the weekend can completely make up for a restless week.
A 2016 study from the same institute found that sleeping in late on Saturday and Sunday "messes with the natural rhythms of your body making you feel worse rather than more rested", The Independent reported at the time.
"They sleep as much during weekdays as during weekends whereas the difference is huge in lower age groups", he explained.
"It fits with what we do know about sleep", he said. When people got enough sleep, it was found that their mortality risk is no higher than the ones who sleep for seven hours a day.
So forget "sleep when you're dead" - it might be more like "don't sleep, and you will be dead".