Poor Quality Sleep in Midlife Linked to Poor Cognition 11 Years Later

The relationship between sleep and cognition has been a popular research topic in recent years, and studies have shown that there is a link between dementia and poor sleep. The direction of that association—whether poor sleep is a risk factor for dementia or dementia symptoms cause poor sleep—has been harder for researchers to determine, explained Yue Leng, Ph.D., an associate professor of psychiatry at the University of California, San Francisco, Weill Institute for Neurosciences.

Leng and her colleagues explored this association further by analyzing data from a prospective cohort. They found that individuals whose sleep is characterized by high restlessness at about 40 years of age may have a higher risk of poor cognitive functioning 11 years later compared with individuals whose sleep is better. Their findings were published in Neurology.

The authors used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, during which participants were assessed every two to five years over 30 years. The current study took place from 2003 to 2005 and included 526 White and Black adults with a mean age of 40 years (58%/42% women/men and 66%/44% White/Black). Participants wore wrist activity monitors for three consecutive days and nights on two occasions about one year apart. The wrist monitors measured both sleep duration and each participant’s sleep fragmentation index, a measure of restlessness during their sleep calculated by measuring the amount of time they spent moving and the amount of time they were still for one minute or less. Participants also reported the times they went to bed and woke up and the quality of their sleep by completing the Pittsburgh Sleep Quality Index.

Cognitive assessments were conducted about 11 years later. Interviewers administered tests that assessed the participants’ processing speed, executive function, working memory, verbal memory, fluency, and global cognitive function.

Participants slept an average of about six hours a night, and 45.6% reported poor-quality sleep. While there was no relationship between sleep duration and cognition, participants with the greatest amount of sleep fragmentation were two to three times more likely than participants with moderate or low sleep fragmentation to have poor cognitive performance 11 years later on nearly all the cognitive measures except verbal memory. These findings did not differ by race or sex.

Leng noted that previous studies have resulted in conflicting findings on whether sleep duration is associated with cognition, but the current study showed no association. “Many studies have shown a U-shaped relationship between sleep duration and cognition,” Leng said. “This study really helps to resolve these conflicting findings. It emphasizes the importance of sleep quality and that we should be paying attention to how fragmented our patients’ sleep may be.”

She also noted that the study found an association, not causation, and it is too early to make conclusions about prevention. More research is needed. Leng and her colleagues are currently looking at how sleep across the different stages of life, including early adulthood, is associated with cognition later in life.

Ebony Dix, M.D., said she would like to see more studies that investigate how risk factors for dementia could be balanced with other lifestyle changes. If more research does show that poor sleep quality is a risk factor for poorer cognition, what can people do to offset those issues? She pointed out that some may not be able to avoid fragmented sleep, such as new parents, those with undiagnosed sleep apnea, or those caring for elderly relatives. Dix is an assistant professor of psychiatry at Yale School of Medicine, medical director of the inpatient geriatric psychiatry unit at Yale New Haven Hospital, and a member of APA’s Council on Geriatric Psychiatry.

“Is it possible to reverse the damage that poor sleep has already done?” she asked. “If a person has a healthy lifestyle and feels generally positive about their sleep habits, could that offset any potential damage caused by fragmented sleep earlier in life? These are some of the questions I’m hoping more research can answer so that we can give patients more direction.”

Sleep, especially among older adults, is an issue that certainly needs more attention, she added. “If you think about older adults and some of the things that disrupt their sleep, there are often issues that their care teams should pay more attention to,” she said. “They may have issues with chronic pain, frequent urination, or other medical issues. Sometimes disrupted sleep may be due to a medication side effect.”

The study was funded by the National Heart, Lung, and Blood Institute. ■