Many people become a little more tired as they grow older, but a new study suggests that a steady increase in daytime sleepiness during the 80s could be an important sign that the brain is changing.
The research, published in Neurology®, the medical journal of the American Academy of Neurology, found that older women who became much sleepier over several years were more likely to develop dementia than women whose sleep stayed stable.
Dementia is not a normal part of aging. It is a group of conditions that slowly damage memory, thinking, reasoning, and the ability to carry out everyday tasks.
Alzheimer’s disease is the most common form of dementia, but there are several other types. Around the world, millions of older adults are living with dementia, and the number is expected to rise as people live longer.
Because there is still no cure for most forms of dementia, scientists are searching for early warning signs that may help doctors identify people at higher risk before severe memory problems appear.
Sleep has become an important area of research because the brain stays very active while we sleep.
During healthy sleep, the brain stores memories, removes waste products, and repairs itself after the day’s activities.
Poor or changing sleep has been linked with several health problems, including heart disease, diabetes, depression, and memory decline.
However, researchers still do not fully understand whether sleep changes contribute to dementia or whether they are one of the earliest signs that the disease has already started developing inside the brain.
To explore this question, researchers led by Dr. Yue Leng from the University of California, San Francisco followed 733 women whose average age was 83 years. At the beginning of the study, none had dementia or major memory problems. The scientists tracked their sleep and brain health for five years.
Instead of relying only on questionnaires, the women wore small wrist devices that recorded when they slept, how long they slept, how often they woke up, how much they rested during the day, and how regular their daily sleep and wake patterns were.
These measurements gave the researchers a much clearer picture of each participant’s daily routine.
By the end of the study, 164 women had developed mild cognitive impairment, which is an early stage of memory and thinking problems that can sometimes progress to dementia. Another 93 women had developed dementia.
The researchers found that sleep patterns changed in more than half of the participants over the five years. About 44% had sleep that stayed stable or even improved slightly.
Around 35% experienced poorer nighttime sleep, including shorter sleep, more waking during the night, and more daytime naps.
The remaining 21% showed a different pattern. They became sleepier over time, sleeping more during both the day and night, having poorer-quality sleep, and showing weaker daily body rhythms that normally help people feel awake during the day and sleepy at night.
When the researchers compared brain health between these groups, they found important differences. Only 8% of women with stable sleep developed dementia. Among women with poorer nighttime sleep, 15% developed dementia.
The highest percentage was seen in the group with increasing sleepiness, where 19% developed dementia.
Even after the scientists considered other factors that could affect dementia risk, including age, education, race, diabetes, and high blood pressure, women whose sleepiness increased over time were still about twice as likely to develop dementia as those with stable sleep.
Surprisingly, women who simply slept worse at night did not have a statistically meaningful increase in dementia risk. This suggests that a gradual increase in overall sleepiness may provide more useful information than poor nighttime sleep alone.
The findings do not prove that becoming sleepier causes dementia. It is possible that changes inside the brain begin years before memory problems become obvious, and those early brain changes may make people feel sleepier during the day. More studies will be needed to understand exactly how sleep and dementia influence each other.
The researchers also noted some limitations. Most participants were white women in their 80s, so the findings may not apply equally to men, younger older adults, or people from different ethnic backgrounds.
Future studies involving more diverse groups will help confirm whether the same pattern is seen in the wider population.
Even so, the study highlights the importance of paying attention to changing sleep habits in later life. A sudden or steady increase in daytime sleepiness should not automatically be dismissed as a normal part of aging. While it does not mean a person will definitely develop dementia, it may be worth discussing these changes with a healthcare professional, especially if they are accompanied by memory or thinking concerns.
The research was supported by the National Institutes of Health and the National Institute on Aging.
It adds to growing evidence that healthy sleep is closely connected with healthy brain aging and may provide valuable clues about future memory health.
If you care about dementia, please read studies about dietary strategies to ward off dementia, and how omega-3 fatty acids fuel your mind.
For more health information, please see recent studies about Choline deficiency linked to Alzheimer’s disease, and what to eat (and avoid) for dementia prevention.
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