From helping you to focus more to improving sports performance, some scientists believe "depositing" sleep for later use can bring a range of benefits.
It's the weekend. The perfect opportunity to switch off the alarm and spend an extra hour or so in bed. For those of us able to enjoy this luxury, sleeping in to catch up on lost rest from earlier in the week is a common tactic. But are we thinking about this the wrong way around? Might it be better to "bank" extra hours of slumber ahead of a busy period to help to counteract the effects of sleepless nights?
Sleep banking – where you snooze for longer over multiple nights ahead of a period where your sleep is likely to be restricted – could well be an effective tactic, according to some researchers. They say it helps the brain to stockpile crucial resources for later deployment, improving alertness and cognitive performance when sleep deprivation hits.
So does it really work?
In 2023, a study of doctors at a hospital in Miami found that banking around 90 minutes of sleep for three nights led to improved performance during two weeks of subsequent night shifts. Other studies have found that the strategy appears to be beneficial for sport performance too. Sleep banking is a common strategy used by competitors during sailing races and appears to reduce the effects of sleep deprivation on errors and reaction times during short sailing regattas.
But the concept of sleep banking remains controversial. Not all researchers agree that it is possible to "deposit" sleep with the intention of withdrawing it later when we need to stay awake for longer. They say it is difficult to unpick whether the body really is "storing" hours asleep for the future or simply catching up on pre-existing sleep debt or need.
One scientific review of the evidence for sleep banking among shift workers has highlighted the risk of potential bias in the way some studies were conducted. They say the research doesn't prove that observed improvements in performance are a direct result of extending sleep in advance.
At the centre of the argument is why our bodies need sleep at all.
"There are many theories as to why we sleep," says Peter Polos, associate professor of sleep medicine at the Hackensack Meridian School of Medicine. "There are metabolic, hormonal, neurological and cognitive issues that are all addressed during our sleep. And it's thought that at least for the brain, it's a time to consolidate thoughts or prioritise important 'files'."
In physiological terms, sleep is essential for the trillions of cells in our bodies. "All your cells need healthy sleep to refuel and repair," says Michael Howell, professor of neurology at the University of Minnesota. "Throughout the course of the day, in our body and in our brain, we have a variety of waste products that build up. It's during sleep that our brain washes them out."
Most adults function best on around seven to nine hours a night, Howell says. "The short sleeper who can get by on four or five hours of sleep is very rare."
That's why a severe sleep deficit is so detrimental. "We can all cope with a lost hour here or there, usually with no consequences," says Polos. "The issue is if it becomes a chronic thing. The effects are cumulative over time and include reduced performance in work or social interactions, lack of motivation and cognitive issues where one feels slower cognitively."
Without sufficient downtime your brain can't sluice out waste, meaning you may struggle to focus and absorb important details in the day that follows, Howell says. "If you're trying to learn a language or a musical instrument, or maybe you're an athlete trying to learn a new skill, you're going to have trouble paying attention and taking the information in," he says. "But then you're also going to have trouble coding the information for long-term storage and use later."
Rupp and her colleagues believe that sleep banking works by giving the brain more time to clear out neuronal waste and replenish the glycogen stores that the brain relies on for energy when blood glucose drops, leaving our brains better able to cope when a bout of sleep deprivation occurs.
Polos says that even if sleep banking does work it shouldn't be seen as a long-term solution. "Don't rely on it as an answer to all your sleep issues or all the demands your work or society's putting on you," he says. Ultimately, changing your relationship with sleep will have a better long-term effect.
"Try to maintain a regular schedule of bed and wake times and get sufficient quality and quantity of sleep," Polos says.