If you're aged 38 plus, you should be getting 7 hours' sleep a night, not 8, finds major new study

More or less than seven hours linked to poorer mental health and cognitive decline

older woman asleep
(Image credit: Getty)

A lot of people have a lot of opinions on the best way to sleep, but one stat that gets bandied about frequently is that you should shoot for eight hours a night. However, a new large-scale study has found that – in the case of those aged 38-73 at least – the ideal amount of sleep per night is actually seven hours. More or less than that duration is linked with poorer cognitive performance and mental health.

The study, run by researchers from the University of Cambridge and Fudan University and published in Nature Aging (opens in new tab) and using data from the UK Biobank, looked at the sleep habits of 500,000 adults aged 38-73, primarily of European ancestry (94% white people). The aim of the research was to identify the optimal sleep duration, using genetic and cognitive factors, brain structure, and mental health as the key measures. Participants answered questions about their sleeping patterns and mental health, as well as undertaking a series of cognitive tests. The study also used brain imaging and genetic data from the majority of the study pool (40,000 participants) to draw its conclusions. 

What are the downsides to sleeping more or less than that ideal seven hours? A longer or shorter sleep duration was linked with poorer cognitive performance, with participants scoring worse in tests assessing their problem-solving skills, memory skills, processing speed, and visual attention. Sleeping too much or too little also had implications for mental health, with those reporting sleeping outside the ideal seven hours also being more likely to show symptoms of depression or anxiety, as well as worse overall wellbeing. Consistency – sleeping the same amount each night – also had an impact, with more consistent sleepers yielding better results. 

"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," said one of the study's authors, Jianfeng Feng, as reported by the University of Cambridge

Professor Barbara Sahakian, another study author from the University of Cambridge, added that, "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."

If you're struggling to get your full seven hours, and you think your bed is to blame, head to our best mattress guide to help you find the right upgrade for you. Some also find using a wakeup light, rather than traditional alarm clock, helps promote a more consistent sleep/wake cycle. 

Ruth is currently on secondment as Sleep Editor for Tom's Guide and TechRadar. The role is an extension of her work on T3, where she ran the site's Wellness channel, which includes sleep, relaxation, yoga and general wellbeing. She was also Outdoors editor, reviewing and writing about everything from camping gear and hiking boots to mountain bikes, drones and paddle boards. She has tested more mattresses than her small flat can handle, and has had to implement a one-in-one-out pillow policy, for fear of getting smothered in the night.