A large-scale Swedish study has found that poor-quality sleep may make the human brain appear up to a year older than its actual age, suggesting that improving sleep could help slow cognitive decline and premature brain aging.

Researchers at the Karolinska Institute in Stockholm analysed data from more than 27,000 middle-aged and elderly adults who provided detailed information about their sleep habits, including sleep duration, insomnia, snoring, and daytime drowsiness. The participants also underwent MRI brain scans to estimate their“biological brain age” - a measure based on the brain's structural and functional characteristics.

The study, published this week, found that individuals with poor sleep tended to have a higher discrepancy between their biological and chronological brain ages.“Those who slept poorly had brains that appeared, on average, one year older than their actual age,” said Abigail Dove, lead researcher at Karolinska's Department of Neurobiology.

To explore why this occurs, scientists examined signs of low-grade inflammation in the body - a known contributor to cognitive decline. They found that inflammation explained more than 10% of the link between poor sleep and accelerated brain aging, underscoring the biological connection between rest and neurological health.

“The good news,” Dove said,“is that sleep quality is something we can improve. Better sleep may protect the brain from premature aging and help preserve cognitive function.”

The findings come amid growing global concern over rising rates of insomnia and mental fatigue linked to modern lifestyles and screen exposure. The Karolinska team said even modest improvements in sleep hygiene could have measurable benefits for long-term brain health.

Previous research from the Mayo Clinic in the United States has shown that chronic insomnia increases the risk of dementia and mild cognitive impairment by as much as 40%. Experts say the latest Swedish study strengthens the evidence that good sleep is not merely restorative but essential for maintaining brain vitality as we age.

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