Quality sleep is crucial for physical health and cognitive well-being. In a new study, scientists discovered a connection between disrupted sleep during middle age and cognitive decline in the future.

Sleep disruption in the 30s and 40s can lead to memory and thinking problems a decade later, according to the study published in the journal Neurology.

"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," said study author Yue Leng. "Our findings indicate that the quality rather than the quantity of sleep matters most for cognitive health in middle age."

The study followed 526 participants with an average age of 40 for 11 years. The average sleep duration and sleep quality of the participants were assessed using a wrist activity monitor, which they wore for three consecutive days on two occasions, approximately one year apart.

Their bedtimes and wake times were noted down in a sleep diary. Participants completed a sleep quality survey with scores ranging from zero to 21 (higher scores indicate poorer sleep quality). Around 46% (239 people) reported poor sleep with a score greater than five. They also completed a series of memory and thinking tests.

The researchers then looked into sleep fragmentation, a measure of repetitive short interruptions of sleep. For estimating sleep fragmentation, they considered the percentage of time spent moving and the time spent immobile for one minute or less during sleep.

The average sleep fragmentation of the participants was 19%. Based on the sleep fragmentation score, the participants were grouped into three.

"Of the 175 people with the most disrupted sleep, 44 had poor cognitive performance 10 years later, compared to 10 of the 176 people with the least disrupted sleep. After adjusting for age, gender, race, and education, people who had the most disrupted sleep had more than twice the odds of having poor cognitive performance when compared to those with the least disrupted sleep. There was no difference in cognitive performance at midlife for those in the middle group compared to the group with the least disrupted sleep," the researchers wrote.

Researchers, however, noted that the amount and the quality of sleep were not associated with cognition in middle age.

Since the study was based on a small sample size, researchers could not fully analyze the potential differences concerning race and gender.

"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 could open up new opportunities for the prevention of Alzheimer's disease later in life," Leng said.

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