Disrupted Sleep During 30s and 40s Can Impair Later Cognitive Functions: Study

Though adults require seven or more hours of sleep, one in three American adults do not get enough sleep, per the CDC.

Young female sleeping with cpap machine for sleep apnea.Independence_Project/Shutterstock

Sleep disruptions experienced by a person in their thirties or forties can result in cognitive decline once they grow older, according to a recent peer-reviewed study.

The study, published in the Neurology journal on Jan. 3, examined the association between sleep quantity and quality among individuals in their mid-30s and late 40s with their cognitive performance. It evaluated 526 individuals who were followed up for 11 years. Researchers looked into sleep fragmentation, which measures the multiple short interruptions to sleep. The study calculated that participants had an average sleep fragmentation of 19.2 percent, meaning roughly a fifth of their sleep was disrupted.

Participants also completed memory and thinking tests. During the study, 45.6 percent of respondents reported having poor sleep quality, with an average of 6.1 hours of sleep per day. People who had the most disrupted sleep during their 30s and 40s were found to be more likely to have memory and thinking issues a decade later.

Out of 175 individuals who experienced the most disrupted sleep, 44 had poor cognitive performance 10 years later. In contrast, just 10 of the 176 individuals with the least disrupted sleep suffered cognitive decline.

This means that while over 25 percent of those with the most disrupted sleep saw cognitive abilities fall over time—only 5.68 percent of those with the least disrupted sleep suffered the same.

“The association between sleep fragmentation and cognitive performance did not differ by race or sex. Objective sleep duration or subjective sleep quality was not associated with cognition in midlife,” the study said. “High sleep fragmentation rather than sleep duration was associated with worse cognition among middle-aged black and white men and women. Sleep quality is important for cognitive health even as early as midlife.”

The participant’s sleep duration was tracked via a wrist monitor during the study period. The subjects recorded their bedtimes and wake times in a sleep diary. They also submitted a sleep quality survey.

“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 from the University of California, San Francisco.

“Our findings indicate that the quality rather than the quantity of sleep matters most for cognitive health in middle age.”

The study was funded by the National Institute on Aging and the National Heart, Lung, and Blood Institute.

A recent study found that a mere 1 percent loss in deep sleep per year could raise the risk of dementia by 27 percent among people aged more than 60.

In an interview, research lead Professor Mattew Pase said that “although we think of dementia as a condition of old age, the diseases that contribute to dementia can actually start at 10 or 20 years before dementia onset.”

If people have dementia in their 70s, the condition often begins to develop around mid-life, he said, while recommending that people maintain their level of deep sleep as they age.

Sleep Quality

According to the U.S. Centers for Disease Control and Prevention (CDC), adults require seven or more hours of sleep per night. However, one in three American adults reportedly do not get enough sleep.

“People often cut back on their sleep for work, for family demands, or even to watch a good show on television. But if not getting enough sleep is a regular part of your routine, you may be at an increased risk for obesity, type 2 diabetes, high blood pressure, heart disease and stroke, poor mental health, and even early death,” the agency said.

In a 2022 Gallup survey, only 32 percent of Americans said they got “excellent” or “very good” sleep the night before. Individuals who rated their general mental health highly were found to be six times more likely to have gotten a good night’s sleep compared to those who rated their mental health “poor” or “fair.”

Good sleep can be highly beneficial to the body. For one, it can lead to weight loss. Between 10:00 p.m. and 2 a.m., growth hormone is produced, which helps break down fat in adults. Between 3 a.m. and 5 a.m., a hormone called cortisol is produced that can break down sugar and fat.

Secondly, quality sleep can clear the mind. A 2019 study found that during the “slow wave sleep” period, the brain will stabilize its cognitive functions and memory.

During this period, the brain’s cerebrospinal fluid will remove metabolic waste from the organ, including beta-amyloid, the aggregation of which is linked to Alzheimer’s.

The CDC points out that while getting sleep is important, “good sleep quality” is crucial. “Signs of poor sleep quality include feeling sleepy or tired even after getting enough sleep, repeatedly waking up during the night, and having symptoms of a sleep disorder.”

It suggested certain habits to improve sleep. The agency advised people to be consistent in their sleeping patterns and to go to bed at the same time each night, getting up at the same time every morning. The bedroom must be “quiet, dark, relaxing, and at a comfortable temperature.”

Before bedtime, large meals and beverages like alcohol and caffeine should be avoided. “Remove electronic devices such as TVs, computers, and phones from the bedroom.” In addition, being physically active during the daytime can help a person get sleep easily during the night, the CDC said.