A study has found that for those in middle to older age seven hours of sleep per night is optimal for them.

Both too much and too little sleep are associated with poorer cognitive performance and mental health, according to researchers.

Scientists examined data from nearly 500,000 adults, aged between 38 and 73, from the UK Biobank. The researchers’ analysis of the data indicated 

that seven hours of sleep per night was the optimal amount for cognitive performance, such as processing speed, visual attention, memory and problem-solving skills. 

It was also optimal for good mental health, with people experiencing more symptoms of anxiety and depression, and worse overall wellbeing, if they reported sleeping for longer or shorter amounts. 

The researchers say one possible reason for the association between insufficient sleep and cognitive decline may be due to the disruption of slow-wave – “deep” – sleep. 

Disruption to this type of sleep has been shown to have a close link with memory consolidation as well as the build-up of amyloid, key protein which, when it misfolds, can cause tangles in the brain.

The reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic make-up and the structure of our brains.