People in their 30s and 50s who have disrupted sleep may be more likely to have memory and thinking problems later in life, according to a new study.
The researchers found that repetitive short interruptions of sleep in midlife were linked to worse cognitive function 11 years later.
They found no association, however, between worse cognitive function and sleep duration or self-reported quality of sleep.
The study was published on Wednesday in Neurology, the medical journal of the American Academy of Neurology. It included more than 500 participants who were followed for over a decade.
More than half of the participants were women and some 44 per cent were Black, but one limitation of the study was that due to the small sample size, they could not fully account for gender or racial differences.
Participants had an average age of 40 and slept for an average of six hours. They wore a wrist monitor for three consecutive days on two occasions one year apart to calculate the averages.
They also reported their sleep in a diary, completed a sleep quality survey, and took memory and thinking tests.
“Most previous studies have examined the association between sleep disturbances and cognitive impairment in late life. This is the first study to suggest that the association between sleep quality and cognition may become prominent as early as in midlife,” Yue Leng, an associate professor of psychiatry at the University of California, San Francisco, and study author.
Prof. Leng added that sleep fragmentation rather than sleep duration was “associated with worse cognition among middle-aged Black and White men and women”.
This means that “sleep quality is important for cognitive health even as early as midlife”.
Sleep fragmentation was measured as restlessness during sleep, based on the sum of time spent moving and time spent immobile.
After adjusting for confounding factors such as age, gender, race, and education, the researchers found that the people who had the most disrupted sleep had more than twice the odds of having cognitive problems compared to those with the least disrupted sleep.
In a separate statement, Prof. Leng pointed out that “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”.
Several studies have found that sleep disturbances could be linked to an increased risk of cognitive problems in older adults. One study published in the journal Sleep in 2013 linked sleep fragmentation in older adults to incident Alzheimer’s disease (AD).
Researchers have also previously linked sleep duration, such as sleeping less than five to six hours a night, to dementia risk for older adults.
Sleep disturbances in midlife, the researchers of this latest study noted, could be caused by physiologic processes such as menopause or psychosocial factors such as work stress.
They added that there is a lack of research “of both objective and subjective sleep, both duration and quality, on cognition in midlife”.
“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,” Prof. Leng said in a statement.
“Future studies could open up new opportunities for the prevention of Alzheimer’s disease later in life”.
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