If you’ve ever muddled through the forgetful funk that follows an all-nighter, you know how skimping on sleep can zap your brain power. Scientists have long known poor sleep messes with cognitive function. Now, a new study published in Neurology suggests the effects of consistent sleep loss on the brain could snowball with time. Researchers found that people with chronic insomnia (who struggle to sleep at least three nights a week for three months or longer) have faster-declining brain function than their age would suggest. The findings are especially relevant for women, as they’re more likely to get insomnia and dementia due to a combination of hormonal and other biological factors, as well as sociocultural ones.
Scientists followed more than 2,750 healthy older adults (without known cognitive issues) for an average of six years, testing their attention, memory, and spatial awareness at various points. Then they compared the results between participants who had a history of insomnia and those who didn’t. What they found: The insomniacs showed a speedier decline in test scores over time than the good sleepers. And after the researchers accounted for other factors that could influence cognitive decline (like education, alcohol use, and depression), they found that people with insomnia were 40% more likely to develop mild cognitive impairment or dementia than those without.
To put that number into perspective, “that’s about the same amount of additional risk for dementia as if you had two cardiometabolic conditions, for instance hypertension and diabetes,” study author Diego Z. Carvalho, MD, a neurologist and sleep medicine physician at Mayo Clinic and a member of the American Academy of Neurology, tells SELF. (These types of diseases are known to have trickle-up effects on brain health over time.) Another way to look at it: It’s like having a brain that’s aged 3.5 years beyond your biological age, Dr. Carvalho says.
Some of the study participants also underwent brain scans to check for key indicators of aging, namely amyloid plaques (buildup of a protein linked to Alzheimer’s disease) and white matter hyperintensities (spots in the brain that suggest damaged blood vessels). And people with insomnia were also asked at the start of the study to share how they’d been sleeping lately. Were they really struggling to notch good shuteye or had they been snoozing more easily than usual? That led to another key finding: People who reported getting rough sleep at the start of the study had more of both brain abnormalities in their initial scans. And those who said they’d been getting better sleep than usual—suggesting that their insomnia symptoms had let up a bit—had fewer white matter hyperintensities in those baseline scans. Taken together, these imaging results serve as even more evidence for the link between sleep and brain health.
That said, it can be tricky to figure out the direction of these findings—did sleep loss cause the brain changes and faster cognitive decline, or was it the other way around? As Dr. Carvalho points out, some of the participants may have had a small amount of brain degeneration before the study started (that wasn’t picked up on tests), which could mess with the circadian rhythm and ultimately worsen sleep.
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