For years, the general rule regarding sleep has been eight hours a night, but a new study from researchers from the University of Cambridge and Fudan University say that might be too much sleep for people in middle age and upwards. So when your FitBit sleep tracker gives you a poor sleep score for only getting 7 hours and 15 minutes of sleep, don’t immediately jump to conclusions about having poor sleep.
In new research published in the scientific journal Nature Aging, scientists examined data from close to 500,000 adults aged 38-73 from the UK Biobank. Participants were asked about sleep patterns, mental health, and well-being, and given a series of cognitive tests, with brain imaging and genetic data available for close to 40,000 of the participants.
By examining this data, researchers found that both lack of and too much sleep were associated with impaired cognitive performance, such as the ability to process information, visual stimuli, memory and problem solving. And the reason for the association between a lack of and too much sleep was due to the disruption of deep sleep, which plays a major role in memory consolidation and brain restoration.
Deep sleep may also help people to purge toxins from their brains — and reduce the harmful deposits of an abnormal protein, amyloid. But too little or too much sleep may create chronic stress.
“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.
So how much sleep do I need?
According to the study, seven hours of sleep per night was the optimal amount of sleep for cognitive performance, but also 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 durations. So cognitive decline in aging appears to have some connection to too little or too much sleep as we age.
Getting a consistent seven hours of sleep was also important to cognitive performance and mental health. And the key here is “consistent,” because interrupted sleep patterns have been found to be associated with inflammation in the body, especially in women. On top of inflammation, if you wake from deep sleep, you’re most likely going to have worse sleep inertia on that day, meaning it takes you longer to “kick back into gear” or “get the day going.”
This isn’t the first time seven hours of sleep corresponded with better health either. Another study released in 2020 by Diabeteologia revealed that too much or too little sleep in people with type 2 diabetes (T2D) was linked to sharply increased death rates, with the effect much larger than that found in the non-diabetic population.
So it might be time to ditch “eight hours of sleep” myth and embrace a new seven hour normal as we age, without hitting the snooze button.