We spend nearly a third of our lives asleep, yet sleep is anything but wasted time. Far from being passive downtime, it is an active and essential process that helps restore the body and protect the brain. When sleep is disrupted, the brain feels the consequences – sometimes in subtle ways that accumulate over years.
In a new study, my colleagues and I examined sleep behaviour and detailed brain MRI scan data in more than 27,000 UK adults between the ages of 40 and 70. We found that people with poor sleep had brains that appeared significantly older than expected based on their actual age.
What does it mean for the brain to “look older”? While we all grow chronologically older at the same pace, some people’s biological clocks can tick faster or slower than others. New advances in brain imaging and artificial intelligence allow researchers to estimate a person’s brain age based on patterns in brain MRI scans, such as loss of brain tissue, thinning of the cortex and damage to blood vessels.
In our study, brain age was estimated using over 1,000 different imaging markers from MRI scans. We first trained a machine learning model on the scans of the healthiest participants – people with no major diseases, whose brains should closely match their chronological age. Once the model “learned” what normal ageing looks like, we applied it to the full study population.
Having a brain age higher than your actual age can be a signal of departure from healthy ageing. Previous research has linked an older-appearing brain to faster cognitive decline, greater dementia risk and even higher risk of early death.
Sleep is complex, and no single measure can tell the whole story of a person’s sleep health. Our study, therefore, focused on five aspects of sleep self-reported by the study participants: their chronotype (“morning” or “evening” person), how many hours they typically sleep (seven to eight hours is considered optimal), whether they experience insomnia, whether they snore and whether they feel excessively sleepy during the day.
These characteristics can interact in synergistic ways. For example, someone with frequent insomnia may also feel more daytime sleepiness, and having a late chronotype may lead to shorter sleep duration. By integrating all five characteristics into a “healthy sleep score”, we captured a fuller picture of overall sleep health.
People with four or five healthy traits had a “healthy” sleep profile, while those with two to three had an “intermediate” profile, and those with zero or one had a “poor” profile.
When we compared brain age across different sleep profiles, the differences were clear. The gap between brain age and chronological age widened by about six months for every one point decrease in healthy sleep score. On average, people with a poor sleep profile had brains that appeared nearly one year older than expected based on their chronological age, while those with a healthy sleep profile showed no such gap.
