A bad night’s sleep can leave you feeling drained the next morning. So it is tempting to think that a long sleep on the weekend can make up for lost hours during the week.

Research suggests that extra sleep can indeed help the body recover from at least some of the effects of sleep deprivation. But there is a catch: sleeping too much or changing your schedule dramatically can also disrupt your body clock.

Adults are generally advised to get around seven to nine hours of sleep a night, while teenagers typically need eight to 10 hours. Yet many people regularly fall short of those targets during the week and try to make up the difference on their days off. One survey of nearly 8,000 US adults found that almost half regularly slept longer on weekends.

Why sleeping in can backfire

Our sleep is controlled by two major systems.

The first is the sleep homeostat, which builds up pressure to sleep the longer we stay awake. The second is our circadian rhythm, the internal body clock that responds to signals such as daylight, darkness, temperature, food and physical activity.

These systems work together to help us become tired at roughly the right time each evening.

A major change to our sleeping hours can interfere with both. If you sleep late on Sunday, for example, you may have less sleep pressure by bedtime. That can make it harder to fall asleep at your usual hour.

The change is not limited to sleep, either. Waking later also changes when you receive daylight and when you eat or move around, which can further affect your body clock.

The result can be a familiar cycle: a long Sunday morning in bed, a late Sunday night and another tired Monday morning.

“It’s like shifting time zones every single week,” says Melynda Casement, a sleep psychologist and director of the University of Oregon Sleep Lab.

But recovery sleep can help

That does not mean catching up on sleep is pointless.

Laboratory studies have found that additional sleep can help repair some of the physical and cognitive effects of sleep deprivation.

In one experiment, people who slept for just two hours in a night showed increased levels of two types of white blood cells, suggesting a stress response in the body. Those who were subsequently allowed up to 10 hours of sleep saw the levels come close to their original baseline.

Another study restricted 11 men who normally slept eight hours a night to just four hours for six consecutive nights. The lack of sleep affected how their bodies processed glucose and responded to insulin, changes associated with a higher risk of type 2 diabetes if they persist.

After the participants were given 12 hours of sleep opportunity for six nights, however, those measures returned to their baseline levels.

Other research has also found that recovery sleep following an all-nighter can restore some aspects of cognitive performance.

Still, sleep debt cannot simply be wiped away with a weekend lie-in. Some abilities, including sustained attention and spatial orientation, appear to remain affected when insufficient sleep continues for weeks or months.

Short naps may also provide some benefit for people who are not getting enough sleep, although researchers generally study naps separately from overnight recovery sleep.

What happens outside the laboratory?

Long-term studies of people’s real-world sleeping habits paint a more complicated picture.

Researchers in Sweden followed more than 40,000 adults for 13 years. Among people under 65, those sleeping six to seven hours a night had the lowest risk of death, while those sleeping five hours or less had a 65% higher mortality risk.

But the researchers found an interesting exception: people who regularly slept longer on weekends appeared to eliminate the additional mortality risk associated with very short weekday sleep.

Other studies have reported possible benefits too. Research involving almost 2,800 South Korean adults found that people who habitually slept too little were more likely to have high blood pressure, while each additional hour of weekend catch-up sleep was associated with a lower risk.

Weekend recovery sleep has also been associated with lower risks of dementia and metabolic syndrome among people who regularly sleep too little during the week.

However, the evidence is not unanimous. A large UK study found no clear relationship between catch-up sleep and the risk of death or cardiovascular disease. Importantly, it also found no evidence that sleeping longer on weekends itself increased those risks.

So should you sleep in?

There is no simple rule that says you must wake up at exactly the same time every day, regardless of how much sleep you have lost.

Till Roenneberg, professor emeritus of chronobiology at LMU Munich’s Institute for Medical Psychology, argues that people should allow themselves to recover from lost sleep.

“Sleep is one of the most important functions in our lives,” he says.

There is, however, an important exception. People with insomnia are generally advised not to compensate for a poor night’s sleep by going to bed much earlier or staying in bed longer, as doing so can disrupt their sleep rhythm further.

For most people, the evidence points towards moderation rather than either extreme.

The sweet spot may be one to two extra hours

So how much extra sleep is enough?

Research increasingly suggests that around one to two additional hours may be a useful middle ground.

Studies in the US and South Korea have linked this amount of weekend catch-up sleep with a lower risk of depression. Other research has associated it with reduced inflammation among habitual short sleepers and lower risks of anxiety and depression among younger people.

In other words, if you have had a particularly bad week of sleep, giving yourself an extra hour or two may be worthwhile.

Just do not expect a weekend spent sleeping until lunchtime to undo months of poor sleep habits.