Ask someone on the street how many hours of sleep you should get a night and chances are they'll tell you '8.' This magic number has been repeated so many times that it's practically gospel at this point. But a new study suggests that, for those age 38 and above, 7 hours is actually the ideal amount of daily shut-eye.
Current NHS advice is that adults need between 7 to 9 hours of sleep, depending on your lifestyle and what your body needs. Children need between 9 and 13 hours.
In research published this week, scientists from the University of Cambridge and Fudan University in China analysed data collected from close to 500,000 adults aged 38-73 years.
How did the study work?
Participants gave details about their sleeping habits, mental health and overall wellbeing, and were subject to a series of cognitive tests. On top of this, brain imaging and genetic data were accessed for nearly 40,000 participants, giving more granular insight into the impact of sleeping habits on their health.
After examining the data, researchers found that too little and too much sleep was associated with impaired cognitive performance. This included participant's problem-solving skills, memory and processing speed – with those who got 7 hours sleep a night coming out top on these tests, on average. This group also reported fewer symptoms of poor mental health, such as signs of anxiety and depression, versus those who clocked longer or shorter durations.
Anything else to know?
The study also showed that consistency matters. Sleeping for 6 hours one day and 9 the next, for example, was linked with feeling tired and groggy.
So, why? The academics say that one possible reason for the link between insufficient sleep and cognitive decline could be due to disruption of slow-wave 'deep' sleep.
Disruption to this type of sleep is associated with the build up in the brain of a protein linked with some forms of dementia. A lack of sleep, they say, could also mean that the brain does not have enough time to clear out toxins, which can lead to issues with cognition later in life.
What did the study's authors say?
Of the findings, Prof Jianfeng Feng from Fudan University said: 'While we can’t say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea. 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.'
Prof Barbara Sahakian from the University of Cambridge, said: 'Getting a good night’s sleep is important at all stages of life, but particularly as we age. Finding ways to improve sleep for older people could be crucial to helping them maintain good mental health and wellbeing and avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias.'
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