Sleep disruptions in 30s and 40s linked to cognitive decline a decade later, study finds

Originally Published: 03 JAN 24 16:14 ET

By Deidre McPhillips, CNN

(CNN) — People who have more interrupted sleep in their 30s and 40s are more than twice as likely to have memory and thinking problems a decade later, according to a new study.

In the early 2000s, the researchers tracked the quality of sleep for hundreds of people during two overnight visits about a year apart, capturing a total of six nights of sleep per person. Sleep quality was assessed using a wrist activity monitor that tracked the amount of sleep people got along with periods of movement to gauge sleep fragmentation, or short, repetitive interruptions of sleep. The participants were about 40 years old, on average, at this point in the study.

More than a decade later, between 2015 and 2016, the researchers analyzed the cognitive ability of 526 of the same participants using standardized interviews and tests of cognitive ability, including processing speed, executive function, memory and fluency.

On average, the study participants were found to sleep about six hours each night, and about a fifth of their sleep time was disrupted. Overall, people experiencing more sleep fragmentation, or with greater share of their sleeping hours spent moving, were more likely to receive poor cognitive scores on all of the tests more than a decade later.

Of the 175 people with the most disrupted sleep, 44 had poor cognitive performance 10 years later, compared with 10 of the 176 people with the least disrupted sleep, the study found.

The research was published Wednesday in Neurology, the medical journal of the American Academy of Neurology

People who slept less or who had higher sleep fragmentation were significantly more likely to be male, to be Black, to have a higher BMI and to have a history of depression or hypertension.

Due to the small sample size, the researchers were unable to fully investigate potential race or gender differences. But after they adjusted for health factors and other demographics, people with the most disrupted sleep were found to be more than twice as likely to score worse than average on the set of cognitive tests compared with those who had the least disrupted sleep.

“Given that signs of Alzheimer’s disease start to accumulate in the brain several decades before symptoms begin, understanding the connection between sleep and cognition earlier in life is critical for understanding the role of sleep problems as a risk factor for the disease,” study author Dr. Yue Leng, an associate professor of psychiatry at the University of California, San Francisco, said in a news release.

Throughout the study, participants were also asked to keep a sleep diary, tracking bedtimes and wake times and assessing their own quality of sleep. However, objective measures of sleep duration and subjective assessments of sleep quality did not correlate to cognition in midlife.

“Our findings indicate that the quality rather than the quantity of sleep matters most for cognitive health in middle age,” Leng said.

People are supposed to get between seven and 10 hours of sleep each night, depending on their age. But 1 in 3 Americans don’t get enough, according to the US Centers for Disease Control and Prevention.

In addition, 50 million to 70 million Americans struggle with sleep disorders such as sleep apnea, insomnia and restless leg syndrome, which can ruin a good night’s shuteye.

The CDC calls that a “public health problem,” because disrupted sleep is associated with a higher risk of conditions including diabetes, stroke, cardiovascular disease – and dementia.

One study from 2021 found that people who reported routinely experiencing difficulty falling asleep had a 49% increased risk of dementia, while those who often woke in the night and had difficulty falling back asleep had a 39% increased risk of dementia. And a study published in October found that chronic loss of slow-wave sleep – the third stage of sleep, during which the body removes unwanted or potentially harmful materials from the brain – may increase the risk of dementia.

“More research is needed to assess the link between sleep disturbances and cognition at different stages of life and to identify if critical life periods exist when sleep is more strongly associated with cognition,” Leng said. “Future studies could open up new opportunities for the prevention of Alzheimer’s disease later in life.”

CNN’s Sandee LaMotte and Kristen Rogers contributed to this report.

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