“It’s partly because of our circadian rhythm, so when you sleep in later, it’s like giving yourself a bit of jet-lag and jet-lag makes you less bright and perky,” Susanna Jernelöv, a psychologist and sleep researcher at Sweden’s Karolinska Institute, told The Local.
“If you sleep a little bit too little all the time, and just catch up on the weekends, you are messing with your circadian rhythms, you should stay on a regular schedule, but that doesn’t really work with most people’s lives.
Jernelöv's claims were backed up by the Norwegian sleep researcher Bjørn Bjorvatn at the University of Bergen who last week told Norway's state broadcaster NRK that lie-ins were almost always counter-productive.
“You should get up and go to bed at about the same time every day,” he said. “Do not sleep in late on weekends. Do not have a lie in. If you get up at 12pm on the weekend, it will take time for your rhythm to adjust back.”
He said that although having a lie in might be most tempting in the autumn and winter months, it was actually the time of the year when it was most important to stick to the same rhythm.