A new study suggests that women in their 80s who gradually become sleepier during the day may face a higher risk of developing dementia.
The research, published in the medical journal Neurology®, found that older women whose sleepiness increased over several years were about twice as likely to develop dementia compared with women whose sleep habits stayed mostly the same.
Neurology® is the official journal of the American Academy of Neurology, which focuses on research about the brain and nervous system. Scientists say the study adds new information about how sleep patterns may be connected with brain health in later life.
Sleep plays an important role in keeping the brain healthy. During sleep, the brain performs many important tasks. It helps store memories, clears waste products from brain cells, and allows the brain to rest and recover from the day’s activities. Because of this, scientists have long believed that poor sleep may be linked to problems with memory and thinking.
Dr. Yue Leng, the lead author of the study from the University of California, San Francisco, explained that researchers are still trying to understand exactly how sleep and dementia are related.
According to Dr. Leng, sleep may both affect and reflect brain health. In other words, sleep changes might increase the risk of memory problems, but they might also be an early sign that brain changes are already beginning.
To explore this question, researchers followed 733 women with an average age of 83. At the beginning of the study, none of the women had signs of dementia or serious memory problems. The scientists then observed them over a period of five years to see how their sleep patterns and cognitive health changed.
During those five years, some participants began to develop thinking and memory problems. By the end of the study, 164 women had developed mild cognitive impairment, which is a condition where memory and thinking skills begin to decline but are not yet severe enough to be called dementia. In addition, 93 women were diagnosed with dementia.
Instead of asking the participants to simply report how well they slept, the researchers used special wrist devices to collect more accurate information.
The women wore these devices at the beginning of the study and again five years later. The devices recorded movement and body rhythms, allowing scientists to estimate when the participants were sleeping, how long they slept, and how often they woke up.
The researchers examined several aspects of sleep. These included nighttime sleep length, sleep quality, daytime napping, and the body’s internal daily clock, also known as the circadian rhythm. This rhythm helps control when people feel awake or sleepy during the day.
Over the five years, the scientists noticed that many of the women experienced significant changes in their sleep patterns. In fact, more than half of the participants showed noticeable changes.
The researchers grouped the women into three categories based on how their sleep changed. About 44 percent had sleep patterns that stayed stable or even improved slightly over time. Around 35 percent developed poorer nighttime sleep, meaning they slept for shorter periods, woke up more often during the night, and took more naps during the day.
The remaining 21 percent of women showed a different pattern. They became sleepier overall. These women slept more during both the day and the night, had lower-quality sleep, and experienced greater disruption in their natural daily rhythms.
The research team then compared how many women in each group later developed dementia. Among those with stable sleep patterns, about 8 percent developed dementia during the study period. In the group with worsening nighttime sleep, about 15 percent developed dementia.
However, the highest risk was found in the group whose sleepiness increased over time. In this group, about 19 percent of women developed dementia.
After taking into account other factors that might influence dementia risk, such as age, race, education level, diabetes, and high blood pressure, the researchers found that the women with increasing sleepiness had about double the risk of dementia compared with those whose sleep remained stable.
Interestingly, the group with poorer nighttime sleep did not show a clearly higher risk once these other factors were considered. This suggests that increasing sleepiness throughout the day and night may be a more important signal than nighttime sleep problems alone.
Dr. Leng said the study highlights how sleep patterns can change significantly in people in their 80s. She believes future studies should look at sleep in a broader way, including daytime naps, nighttime sleep quality, and changes in the body’s daily rhythms. Understanding these patterns may help scientists learn more about how dementia develops.
The researchers also noted a limitation in their study. Most of the participants were white women, which means the results may not fully represent people from other racial or ethnic backgrounds. Future studies with more diverse groups will be needed to confirm the findings.
The study was supported by funding from the National Institutes of Health and the National Institute on Aging, two major organizations that support medical research on aging and brain health.
Although the research does not prove that sleepiness directly causes dementia, it suggests that major changes in sleep patterns may be an early warning sign of changes happening in the brain. Paying attention to sleep habits in older adults may therefore help doctors better understand and monitor brain health over time.
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