The Guardian »

The study of nearly 500,000 adults aged between 38 and 73 found that both too much and too little sleep were linked with worse cognitive performance and mental health, including anxiety and depression. A consistent amount of sleep also appeared to be beneficial.

Prof Barbara Sahakian, from Cambridge University’s department of psychiatry, said: “For every hour that you moved away from seven hours you got worse. It’s very clear that the processes that go on in our brain during sleep are very important for maintaining our physical and mental health.”

Getting a good night’s sleep, she added, was important at all stages of life, but particularly as people aged. “I think it is as important as getting exercise.”

A possible reason for the link between insufficient sleep and cognitive decline may be the disruption of slow-wave, or deep, sleep, which has been shown to be important for memory consolidation. A lack of deep sleep could also prevent the brain from clearing toxins effectively.