Disrupted sleep can cause memory and thinking problems, study finds

In a groundbreaking study published in Neurology®, researchers have uncovered a compelling association between disrupted sleep in one's 30s and 40s and the likelihood of experiencing memory and thinking problems a decade later.

While the study does not establish a causal link between sleep quality and cognitive decline, it provides valuable insights into the intricate relationship between sleep patterns and brain health.

Lead author of the study, Yue Leng, PhD, from the University of California, San Francisco, emphasized the significance of understanding the connection between sleep and cognition earlier in life, especially considering that Alzheimer's disease markers begin accumulating in the brain decades before symptoms manifest.

Dr. Leng stated, "Our findings indicate that the quality rather than the quantity of sleep matters most for cognitive health in middle age."

The research involved 526 participants with an average age of 40, who were closely monitored over an 11-year period. To gauge sleep duration and quality, participants wore wrist activity monitors for three consecutive days on two separate occasions, roughly one year apart. The study revealed that, on average, participants slept for six hours each night.

In addition to monitoring sleep duration, participants provided information on their bedtime and wake time through sleep diaries. Furthermore, they completed a sleep quality survey, yielding scores ranging from zero to 21, with higher scores indicating poorer sleep quality. Alarmingly, 46% of participants reported experiencing poor sleep, defined as having a score greater than five.

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To assess memory and thinking abilities, participants underwent a battery of cognitive tests. Researchers also examined a sleep parameter known as "sleep fragmentation," which measures the frequency of short interruptions during sleep. This parameter considers both the time spent moving and the time spent not moving for one minute or less during sleep. The study found that participants, on average, experienced a sleep fragmentation score of 19%.

Based on their sleep fragmentation scores, participants were divided into three groups. Among the 175 individuals with the most disrupted sleep, 44 exhibited poor cognitive performance a decade later, compared to just 10 of the 176 individuals with the least disrupted sleep.

Even after adjusting for variables such as age, gender, race, and education, the research revealed that those with the most disrupted sleep had over twice the odds of experiencing poor cognitive performance in middle age, compared to those with the least disrupted sleep. Surprisingly, there were no discernible differences in cognitive performance between the middle group and the group with the least disrupted sleep.

Dr. Leng pointed out, "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. Future studies in this area could pave the way for innovative approaches to Alzheimer's disease prevention."

Crucially, the study did not establish any substantial associations between the amount of time spent sleeping or participants' own reports of sleep quality and cognitive performance in middle age.

However, it is essential to note that this study has its limitations. Due to its relatively small sample size, the researchers were unable to comprehensively investigate potential race or gender differences.

Funded by the National Institute on Aging and the National Heart, Lung, and Blood Institute, this research opens up new avenues for understanding the intricate relationship between sleep patterns and cognitive health. It underscores the importance of quality sleep in middle age as a potential factor in the development of cognitive issues later in life.

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