even hours is the ideal amount of sleep for those in their middle age and upwards, according to a new study.
Researchers from the University of Cambridge found that too little or too much sleep was associated with poorer cognitive performance and mental health issues, including anxiety and depression.
The study involved nearly 500,000 adults aged between 38 and 73, with participants asked about their sleeping patterns and overall wellbeing before going through a series of cognitive tests.
It used data from the UK BioBank and included brain imaging and genetic data for some 40,000 participants.
Those who got more or less than seven hours per night scored worse in tests for attention span, thinking speed and problem solving.
The findings challenge the widely held belief among health experts that eight hours sleep provides the best overall health benefits. The NHS continues to recommend between six to nine hours for adults.
Scientists pointed to the disruption to slow-wave deep sleep that many of the participants who had less than seven hours sleep were experiencing.
They noted that disruption to this type of sleep has been shown to have a close link with the build-up of amyloid – a protein which can cause “tangles” in the brain and affect its ability to rid itself of toxins.
Meanwhile, those who got seven hours of sleep per night had the best cognitive performance and reported lower levels of depression and anxiety.
The study, published in the journal Nature Aging on Thursday, recommended getting a consistent amount of sleep every day and avoiding fluctuation in duration.
Prof Barbara Sahakian, from Cambridge University’s department of psychiatry, 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.”
Professor Jianfeng Feng from Fudan University in China 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.”