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Mr. A, a man in his 50s, goes to bed at midnight and wakes up at 7 a.m. every day. On paper, he gets exactly seven hours of sleep—right in line with the recommended duration by the Korean Society of Sleep Medicine. He believed there was nothing wrong with his sleep.

However, his daytime condition told a completely different story. Every morning, his mind felt foggy and unrefreshed. By the afternoon, his concentration would plummet, and even coffee couldn’t keep him going. He found himself getting irritated over minor mistakes by his subordinates, and even catching up on sleep over the weekend didn’t relieve his chronic fatigue.

What Mr. A overlooked was a crucial fact: sleep cannot be evaluated solely by how many hours you spend in bed. Two people may both sleep seven hours, yet one wakes up with a brain cleared of toxins, while the other accumulates cellular stress and waste overnight—accelerating “biological aging.”

A research team from Concordia University in Canada analyzed sleep patterns, brain MRI scans, mental health, cognitive function, and lifestyle data from 770 healthy adults. They classified sleep into five distinct types in a study published last October in the international journal PLOS Biology. What makes this study notable is that it looked at the “big picture” of sleep rather than focusing only on duration or satisfaction.

Aurore Perrault, the study’s first author and a researcher at Macquarie University’s Sleep and Circadian Research Group, said in an email interview with JoongAng Ilbo, “Sleep duration is important, but it seems even more important whether you’ve slept well enough.” She added, “Rather than fixating on how many hours you slept, you should ask yourself whether you slept well and feel satisfied with your sleep.”

What’s even more striking is that certain sleep types are linked not just to fatigue, but also to depression, anxiety, cognitive performance, and even personality changes. Combined with recent findings on sleep and activity rhythms, disrupted sleep patterns may allow toxins to accumulate in the brain—potentially leading directly to dementia.

So, what type of sleeper are you? And how fast is your sleep pattern turning your biological clock forward? Here’s a closer look at the key reset points you should address tonight, based on different sleep profiles.

🧴 Sleep cleans the brain

From a neuroscience perspective, sleep is not just rest. At night, the brain activates a cleansing mechanism known as the “glymphatic system.”

Cerebrospinal fluid flows between brain cells, washing away waste that accumulates during the day. Harmful substances associated with dementia, such as beta-amyloid and tau proteins, are also cleared during this process. This system is especially active during deep sleep early in the night. When sleep quality is poor or frequently interrupted, the efficiency of this cleaning system drops sharply, allowing waste to build up and accelerating neurodegeneration.

Recent research has gone a step further by examining aging speed itself. A study published this May in JAMA Network Open by researchers at Johns Hopkins University analyzed the activity levels of 207 middle-aged and older adults over one week and compared them with “DNA methylation-based aging clocks.”

The results pointed clearly in one direction: the more regular and robust a person’s daily rhythm of activity and rest—meaning going to bed and waking up at consistent times, staying active during the day, and resting well at night—the slower their biological aging clocks, known as GrimAge and PhenoAge, tended to run. Conversely, irregular and inconsistent rhythms were associated with faster aging.

Interestingly, this relationship was more pronounced in women than in men, suggesting that managing sleep rhythms may have a more direct impact on aging in women.

That said, this was a cross-sectional study, so it does not prove that poor sleep directly causes aging. Still, one thing is clear: disrupted sleep rhythms and accelerated aging tend to go hand in hand. When your sleep rhythm collapses, the hands of your biological clock begin to spin faster.

🛏️ Five sleep profiles identified by science—and their warning signs

The five types identified by the Concordia research team can be understood as different ways sleep breaks down. These are not diseases, but “patterns.” A person may fall into multiple categories, and these patterns can change over time.

During busy periods, someone might exhibit a short sleep pattern; under high stress, they may shift into generalized insomnia; with aging, they might develop fragmented sleep. Understanding your dominant pattern is essential, as each type requires a completely different approach to improvement.

So, what is the real culprit that overstimulates your brain networks and erodes your cognitive abilities?

Source: 중앙일보 (https://www.joongang.co.kr/article/25440354)