Older women who become sleepier during the day over a five-year period may have a higher risk of developing dementia, according to a new study published in Neurology®, the journal of the American Academy of Neurology.
While the study doesn’t prove that increased sleepiness causes dementia, it does show a strong link between the two.
The research focused on women in their 80s and found that those with growing daytime sleepiness were twice as likely to develop dementia compared to those with stable sleep habits.
“Sleep plays an important role in keeping our minds healthy,” said lead researcher Dr. Yue Leng from the University of California, San Francisco. “It helps the brain rest and recover, which supports memory and clear thinking.
But we still don’t fully understand how sleep changes as we age and how that might relate to dementia. Our study suggests that sleep issues and cognitive decline may be closely connected in older women.”
The study included 733 women with an average age of 83. None of the participants had dementia or mild cognitive impairment at the start of the study. Over five years, they were monitored to see how their sleep patterns changed and whether they developed memory problems.
By the end of the study, 22% (164 women) had developed mild cognitive impairment, and 13% (93 women) had developed dementia. The women wore wrist devices for three days at both the beginning and end of the study.
These devices tracked their sleep habits, including how much they slept at night, how much they napped during the day, and how their body’s internal clock (called the circadian rhythm) changed over time.
More than half of the participants—56%—had major changes in their sleep patterns during the study. The researchers divided them into three groups: those whose sleep remained stable or slightly improved (44%), those whose nighttime sleep got worse (35%), and those who became sleepier both day and night (21%).
The results showed that 8% of women in the stable sleep group developed dementia, compared to 15% in the group with declining nighttime sleep, and 19% in the group with increasing sleepiness.
Even after accounting for factors like age, education, race, diabetes, and high blood pressure, the researchers found that women in the increasing sleepiness group were twice as likely to develop dementia as those in the stable sleep group. Interestingly, no increased dementia risk was found in the group with declining nighttime sleep alone.
Dr. Leng noted, “We saw big changes in sleeping, napping, and circadian rhythms in just five years for women in their 80s. This shows that future studies should look at all parts of daily sleep habits to understand how they relate to dementia.”
One limitation of the study was that most of the participants were white, so the findings may not apply to more diverse groups.
The research was supported by the National Institutes of Health and the National Institute on Aging.
The study is published in Neurology.
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