Think 8 hours of sleep is best? Think again! | DW | 05.05.2022


Most of us have internalized it as a rule: A full night of sleep means eight hours for adults. But that may no longer be true once people hit a certain age.

A team of researchers from the University of Cambridge in the UK and Fudan University in China have found that seven hours of sleep may be the ideal amount of shut-eye for middle-aged and elderly people.

In a study published in the journal Nature Aging, the researchers said they found that seven hours of sleep was best for cognitive performance and good mental health.

The researchers examined data from nearly 500,000 participants aged 38 to 73 years and found that insufficient ― but also excessive ― sleep were associated with impaired cognitive performance and worse mental health.

Study participants reported their sleep patterns and also answered questions about their well-being and mental health. They completed a number of cognitive tasks that tested their processing speed, visual attention, memory and problem-solving skills. And those who had had an uninterrupted seven hours of sleep did better across the board.

There is one caveat, though: 94% of the participants were white, so it’s unclear whether the results are true for people of color and other ethnic or cultural backgrounds.

Another important factor is consistency. The best results were seen in people who showed little fluctuation in their sleep patterns over long periods of time and who stuck to the seven hours.

In other words, getting four hours of sleep ahead of a big meeting cannot be “made up” by sleeping 10 hours the next night.

Interrupted sleep: Risk of dementia

“Getting a good night’s sleep is important at all stages of life, but particularly as we age,” said Barbara Sahakian, a professor at Cambridge University and co-author of the study.

The researchers said a lack of sleep is likely to hamper the brain’s process of ridding itself of toxins. They also say that a disruption of slow-wave or deep sleep may be responsible for cognitive decline.

When deep sleep is disturbed, it affects memory consolidation and that can lead to the buildup of amyloid, a protein that can — if it fails to function as it should — cause “tangles” in the brain that are characteristic of some forms of dementia.

Insufficient or excessive sleep could be a risk factor for cognitive decline in ageing.

“While we can’t say conclusively that too little or too much sleep causes cognitive problems, our analysis appears to support this idea,” said Jianfeng Feng, a brain scientist and professor at Fudan University. “But the reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic makeup and the structure of our brains.”

Length of sleep affects brain structure

The researchers also looked at brain imaging and genetic data, but those data were only available for less than 40,000 of the participants.

That data showed that the amount of sleep could be linked to differences in the structure of brain regions like the hippocampus, which is considered the memory and learning center of the brain, and the precentral cortex, which is responsible for executing voluntary movements.

Since the risk of developing Alzheimer’s and dementia — ageing diseases that come with cognitive impairments — has been linked to sleep duration, the researchers said that further work in the field of sleep science is essential.

“Finding ways to improve sleep for older people could be crucial in helping them maintain good mental health and well-being and [their] avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias,” Sahakian said.

Edited by: Zulfikar Abbany

  • Engraving of a person trying to drag another person from a bed Joseph and Potiphar's Wife | Radierung von Rembrandt (Wikipedia/Rijksmuseum Amsterdam)

    Sleep in art

    Joseph and Potiphar’s Wife by Rembrandt

    In this 1643 illustration, Dutch baroque artist Rembrandt van Rijn (1606-1669) painted a biblical scene known as Joseph and Potiphar’s Wife. The wife of Potiphar, an Egyptian official, tries to seduce Joseph, their slave turned personal guard. Lying in bed half naked, she tugs at Joseph’s sleeve — but he’s clearly more than reluctant.

  • Painting of a girls lying on a sofa (Wikipedia/The Athenaeum)

    Sleep in art

    Mette Asleep on a Sofa, by Paul Gauguin

    The above young woman resting on a recamier — a sofa without a backrest — is Mette-Sophie Gad. French painter Paul Gauguin (1848-1903) captured his wife in her nightgown in 1875.

  • Woman resting her head on her hand, sitting at a table (wikipedia/Metropolitan Museum of Art)

    Sleep in art

    A Girl Asleep, by Jan Vermeer

    The 1657 oil painting A Girl Asleep by Jan Vermeer (1632-1675), a renowned Dutch painter, shows a woman sitting at a table, eyes closed, head in hand. She was long presumed to be a maid, but her high-quality clothing suggests that she is in fact the artist’s wife.

  • Painting of bed with rumpled sheets (wikipedia/The Yorck Project)

    Sleep in art

    A Bedroom, by William Turner

    In a series of paintings in 1827, British artist Joseph Mallord William Turner (1775-1851) portrayed bedrooms at Petworth, the country home of a wealthy patron. A Bedroom gives the viewer a glimpse into an intimate, private setting.

  •  Picasso painting of a female figure asleep in a chair (flickr/Fort Greene Focus)

    Sleep in art

    The Dream, by Pablo Picasso

    Spain’s Pablo Picasso (1881-1973) painted his lover Marie-Therese Walter in 1932. Picasso was 22 at the time, and is said to have painted the colorful portrait of the young woman asleep in a chair in just one afternoon.

  • Snoopy asleep on his dog house (Imago/Cinema Publishers Collection)

    Sleep in art

    Sleeping Snoopy, by Charles M. Schulz

    US cartoonist Charles M. Schulz (1922-2000) has portrayed Snoopy, the famous beagle in the Peanuts series, countless times asleep. Sometimes he sleeps sitting up, or lying on his belly on the ground — or, typically, the dog is on his back on the roof of his famous red dog house.

    Author: Alexandra Mölleken (db)

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