To regain control and act on the quality of our nights, we should focus more on its quantity.
A team of Sino-British researchers from the University of Cambridge and Fudan have shown that, once past the forties, seven hours of sleep - no more, no less - are necessary to maintain mental health.
This work was published Thursday, April 28 in the journal
Nature Aging
.
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More attention, less anxiety
To arrive at this result, the researchers analyzed the genetic data of 500,000 individuals aged 38 to 73 (94% white people), from the UK Biobank, a biomedical database.
At the same time, the sample was asked about their sleep habits, mental health and general well-being.
This questionnaire was followed by a series of cognitive tests.
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After the analysis, it was found that those who slept 7 hours a night showed better results in tests relating to information processing speed, visual attention, memory and the ability to solve problems.
The latter also showed less visible signs of anxiety and depression, compared to light and heavy sleepers.
Using brain imaging data from 40,000 participants, the research team also succeeded in identifying the area of the brain impacted by sleepers' sleep duration.
This is the one containing the hippocampus, considered the memory center of the brain.
The slow-to-deep sleep trail
While these studies suggest a link between insufficient rest and cognitive decline, they do not, for the time being, confirm a cause and effect relationship.
Among the avenues considered by research to explain the link, we find that of a disturbance of the phases of slow to deep sleep, which are decisive in the consolidation of memory.
"Getting a good night's sleep is important at all stages of life, but especially as we get older," says Professor Barbara Sahakian from Cambridge University's Department of Psychiatry.
Finding ways to improve sleep in older adults could be crucial in helping them maintain good mental health and ward off cognitive decline, especially for patients with psychiatric disorders and dementias.