Seven hours is the ideal amount of sleep people middle aged and older need, according to experts.

They found that too little or too much sleep can lead to poorer cognitive performance and mental health.

This affects things like processing speed, visual attention, memory and problem-solving skills.

Sleeping patterns and habits of almost 500,000 people aged between 38 and 73-years-old were studied.

The research shows that those who slept longer or shorter than seven hours were more likely to experience symptoms of anxiety and depression, and worse overall wellbeing.

“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,” said Professor Jianfeng Feng from Fudan University in China.

“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.”

Disruption to deep sleep may be one reason for the link between insufficient sleep and cognitive decline, scientists believe.

Not getting enough shut eye can also have an effect on the brain’s ability to clear out toxins.

“Getting a good night’s sleep is important at all stages of life, but particularly as we age,” said Professor Barbara Sahakian from the University of Cambridge.

“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.”

Their findings support previous studies which link sleep duration and the risk of developing Alzheimer’s disease and dementia.

Cognitive decline is one of the major symptoms for both.

The research was published in the Nature Aging journal.

This story originally appeared on The Sun and was reproduced here with permission.