Eight hours of sleep is typically touted as a good night's rest, but a new study would beg to differ.
Seven hours have been pinpointed as the optimal amount for a specific 35-year age group by researchers from the University of Cambridge and Fudan University.
To be specific, it is said adults from the age of 38 to 73 would most benefit from seven hours of shut-eye.
The study found that both too much and too little sleep resulted in the same consequences - poorer cognitive performance and mental health.
As we get older, we often see changes in their sleep from difficulty falling asleep to a bad nights' rest, but good sleep is especially important as we age.
Sleep disturbances may contribute to cognitive decline - a main symptom of Alzheimer's and dementia - and psychiatric disorders in the ageing population.
The study, which was published in the medical journal Nature Aging, examined data from almost 500,000 adults from the UK Biobank, a large database with in-depth genetic and health information.
Participants were asked about their sleeping patterns, mental health and wellbeing, and took part in a series of cognitive tests.
The analysis found that insufficient and excessive sleep was associated with impaired cognitive performance, such as processing speed, visual attention, memory and problem-solving skills.
A seven hour rest was the optimal amount for cognitive performance and good mental health.
Any more or less and people experienced more anxiety and depression symptoms and overall worse wellbeing.
Researchers say one possible reason may be the disruption of slow-wave sleep also known as 'deep' sleep.
Disruption to deep sleep has been shown to have a close link with a build-up of amyloid - a key protein which, when it misfolds, can cause 'tangles' in the brain characteristic of some forms of dementia.
Not getting enough of this sort of sleep may hamper our abilities to make memories as well as get rid of toxins in the brain.
It's also important to get a consistent seven hours of sleep every night as 'making up' lost sleep doesn't cut it.
Previous studies have also shown that interrupted sleep patterns are associated with increased inflammation, which, for older people, can mean being more vulnerable to age-related diseases.
Researchers say their findings suggest that insufficient or excessive sleep duration may be a risk factor for cognitive decline in ageing.
This is supported by previous studies that have reported a link between sleep duration and the risk of developing Alzheimer's disease and dementia, in which cognitive decline is a hallmark symptom.
"Getting a good night's sleep is important at all stages of life, but particularly as we age," said Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge, one of the study's authors.
"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."
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