New studies show no connection between short sleep and brain atrophy. This suggests that six hours of sleep can work just as well for some people as seven hours, according to sleep researchers.

Does everyone need the same amount of sleep? Expert believes six hours might be enough for some

“There’s no reason to lie awake at night worrying about not getting enough sleep,” a sleep expert says.

Enough research is available to show that too little sleep is bad for our health.

People who sleep too much and those who sleep too little both have poorer mental health and memory.

More than nine hours of sleep is deemed to be too much, fewer than six hours too little. A place in between is recommended as the ideal for adults.

But what about people who sleep six hours or less? Researchers have now examined the brains of these short sleepers.

Anders Fjell is a professor at the University of Oslo.

“The results indicate that some people can cope with less sleep without it having any obvious negative impact on their brain,” says Anders Fjell, a researcher at the University of Oslo.

Fjell is one of the researchers behind two new studies on sleep length and the brain, published in The Journal of Neuroscience and Nature Human Behaviour.

No link between brain atrophy and short sleep

Fjell and his colleagues have looked at the brain and how it is affected by sleep. The researchers found no connection between sleep length and brain atrophy.

They believe this finding suggests that normal brains gauge adequate sleep and have good control over exactly how much the body needs.

According to Fjell, the study confirms that some people can sleep less than others – at least as far as brain health is concerned.

He points out that people have big individual differences in how much sleep they need to feel and function optimally.

For example, we don’t know what would happen to the brain if people who usually sleep eight hours, start sleeping six hours, or vice versa.

“The biggest consequence of too little sleep is that you might become drowsy during the day,” says Fjell.

Previous research shows similar findings

Bjørn Bjorvatn is a sleep expert at the University of Bergen.

He confirms that there are so-called short sleepers in the population.

“These are people who don’t need as much sleep and who function excellently, without any increased risk of illness or ailments,” he says.

Bjørn Bjorvatn is a professor at the University of Bergen.

Bjorvatn believes the new studies indicate that six hours of sleep can work just as well for some people as seven hours for others.

Problems with self-reporting

The studies are based on surveys and MRI images of the brain.

In the MRI images, researchers were able to see if anything indicated brain atrophy in individuals who reported that they normally slept for six hours or less.

And they found nothing to indicate brain atrophy.

The problem with using surveys is that respondents may not remember events accurately. They might exaggerate sleep difficulties or downplay problems. Researchers would thus not receive completely correct information.

An alternative to surveys are expensive and complicated studies in sleep laboratories. This method allows researchers to observe the participants in experiments and obtain objective measures of how long the participants sleep, as well as how deep their sleep is.

Fjell and colleagues checked the participants' answers with information from sensors worn by some of the participants on their wrists, which measure the length of sleep quite accurately.

Sleep is subjective

Bjorvatn believes that surveys such as the one in this study are not necessarily a weakness in studies about sleep.

“This field is often based on subjective information,” he says.

Insomnia, for example, is a diagnosis that is solely based on what the patient experiences.

“For that, no objective data is necessary,” he says.

As individual as height and intelligence

According to Bjorvatn, researchers have already known about short sleep and brain health for quite some time.

“The results are both in line with previous research and my own thoughts on this,” he says. “But it’s still good to have such thorough and impressive studies that examine brain changes."

Because the length of sleep and the need for sleep are very individual, just like height, weight, intelligence, nose size, and so on, he adds.

Concerned about those who choose not to sleep

Previous studies have shown that diseases affecting the brain, like Alzheimer's and Parkinson's, are linked to poorer sleep quality.

“A number of studies state that sleeping less than six hours is associated with ill health, such as increased risk of anxiety and depression, overweight and obesity, diabetes, cardiovascular diseases, cancer, and increased mortality,” says Bjorvatn.

“But that’s probably because a lot of people who sleep less than six hours actually need more sleep. I’m most concerned about people who sleep less than six hours because they choose not to sleep. In other words, they prioritise other things than sleeping,” he says.

It is not only people with sleep problems or insomnia who have periods of little sleep. Parents of young children also struggle to get much-needed hours of shuteye: a British study from 2019 shows that new mothers sleep one hour less per night in the first three months after giving birth than before they became pregnant.

The same study shows that parents have their night's sleep disrupted for a full six years after a child’s birth.

People who work night shifts also seem to be particularly prone to sleep issues. Doctors, for example, can become exhausted and unfocused from night work.

Not worried about natural short sleepers

“I’m not worried about people who sleep less than six hours and who don’t feel tired and fatigued – so those who can be considered natural short sleepers,” says Bjorvatn.

Short sleepers are simply lucky to get by on little sleep.

Anders Fjell agrees. 

“There’s no reason to lie awake at night worrying about not getting enough sleep,” he says.

“But, as I said, there’s a large group of people who don’t prioritise sleep enough and sleep too little for that reason. They have an increased risk of ill health and should increase how long they sleep," he concludes.


Fjell et al. Is Short Sleep Bad for the Brain? Brain Structure and Cognitive Function in Short SleepersThe Journal of Neuroscience, 2023. DOI: 10.1523/JNEUROSCI.2330-22.2023

Fjell et al. No phenotypic or genotypic evidence for a link between sleep duration and brain atrophyNature Human Behaviour, vol. 7, 2023. DOI: 10.1038/s41562-023-01707-5


Translated by Ingrid P. Nuse

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