▲ Galaxy Watch
"You must sleep 7 to 8 hours a day to be healthy."
This widely accepted sleep formula is being challenged.
The largest-ever wearable device study, which analyzed actual sleep data from Samsung Galaxy Watch users, has confirmed that the amount of sleep needed varies significantly from person to person.
According to the latest issue of the international journal SLEEP, a joint research team from Sungshin Women's University, Samsung Medical Center, Samsung Electronics, and Harvard Medical School published a paper based on sleep data from 274,128 healthy adults in the United States who wore Samsung Galaxy Watches.
The most significant feature of this study is that it objectively tracked how long people sleep in their actual daily lives over a long period, rather than in a hospital setting.
While previous sleep studies often relied on surveys of hundreds or thousands of people or limited laboratory tests, this study analyzed the actual sleep patterns of hundreds of thousands of individuals using smartwatches equipped with the same algorithm.
Through this, the research team concluded that the conventional concept of a "standard recommended sleep duration" may be far from reality.
In fact, while the overall average sleep duration was 7 hours and 34 minutes, there were vast individual differences.
The 10th to 90th percentile range of sleep duration among all participants spanned from 6 hours and 30 minutes to 9 hours.
This shows how limited the "average" standard can be, as even among healthy adults, there is a difference of more than two hours in daily sleep time.
Based on these results, the research team concluded that sleep duration is highly personal and that there is no single "correct" sleep time that applies to everyone.
The point is that what matters may not be a fixed sleep duration, but the recovery signals sent by one's own body.
Professor Seo Soo-yeon of the Department of Psychology at Sungshin Women's University, the corresponding author of the paper, stated, "While 7 to 8 hours of sleep is generally recommended, big data analysis using the Galaxy Watch shows that there is no single 'correct' sleep time for everyone." She added, "Rather than obsessing over a specific number, it is more important to look at whether you feel sufficiently rested and are functioning properly during the day."
The study also presented results that contradict the common belief that "sleep decreases with age."
The most sleep-deprived age group among Americans was not the elderly, but those in their 40s.
The average sleep duration for those aged 40 to 49 was 7 hours and 32 minutes, the shortest among all age groups.
Notably, 25.1% of this age group slept less than 7 hours a day.
People in their 40s also showed the strongest tendency to "catch up" on sleep on weekends that they missed during the work week.
Their weekend sleep time increased by an average of 34 minutes compared to weekdays, the largest increase across all age groups.
The research team interprets this as the reality of middle age, where work, child-rearing, and caring for aging parents overlap, creating "chronic sleep debt."
In contrast, the average sleep duration for those aged 60 to 69 was 7 hours and 45 minutes, the longest.
Overall, a "U-shaped pattern" was observed, with younger and older age groups sleeping longer and the middle-aged group sleeping the least.
By gender, women were found to sleep an average of about 18 minutes longer than men in all age groups.
This study is also significant in that it shows consumer wearable devices like smartwatches are evolving beyond simple health management tools into actual medical research platforms.
The research team estimated that the sleep measurement values of the Samsung Galaxy Watch had an average error of less than 10 minutes when compared to polysomnography, the standard clinical test for sleep.
Professor Eric S. Zhou, a sleep medicine expert at Harvard Medical School, evaluated the findings, stating, "The sleep standard distribution presented in this study can serve as a practical reference for doctors when consulting with patients or when establishing public health sleep guidelines in the future."
(Photo: Courtesy of Samsung Electronics, Yonhap News)
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