The ideal amount of sleep varies from person to person, but the Korean Sleep Research Society recommends six to eight hours of sleep per day as desirable. Now, a study has drawn attention by overturning the conventional belief that "you must sleep seven to eight hours a day for your health." In the largest-ever wearable study analyzing actual sleep data from Samsung Galaxy Watch users, researchers newly confirmed that the optimal amount of sleep differs greatly from individual to individual.
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 research paper based on sleep data from 274,128 healthy adults in the United States who wore the Samsung Galaxy Watch. The study is notable for analyzing the actual sleep patterns of hundreds of thousands of people using wearable devices equipped with the same algorithm.
The analysis found that the overall average sleep duration among subjects was 7 hours and 34 minutes, but individual differences were very large. The 10th to 90th percentile range of sleep duration among all participants stretched from 6 hours 30 minutes to 9 hours. The research team explained that since daily sleep duration differs by more than two hours even among healthy adults, the standard of an "average" is meaningless.
The research team concluded that sleep duration is highly individual, and that there is no single "correct sleep duration" that applies to everyone. The point is that what matters is not a fixed sleep duration but the recovery signals one's own body sends.
Suh Su-yeon, a professor of psychology at Sungshin Women's University and the paper's corresponding author, said, "Generally, seven to eight hours of sleep per day is recommended, but big-data analysis using the Galaxy Watch showed that there is no single 'correct' sleep duration that applies to everyone." She added, "Rather than obsessing over a specific number, it is more important to examine whether you have rested enough and whether you are functioning properly during the day."
Older People Don't Sleep Less in the Morning? No
The research team also presented findings that differ from the conventional belief that "people sleep less as they age." The age group with the least sleep 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. In particular, 25.1% of this age group did not even sleep a full seven hours a day. The research team interprets that the reality of middle age — where work, child-rearing, and caring for parents overlap simultaneously — is creating "chronic sleep debt."
By contrast, the average sleep duration for those aged 60 to 69 was the longest at 7 hours and 45 minutes. Overall, a "U-shaped pattern" was observed, with younger and older groups sleeping longer and the middle-aged group sleeping the shortest. By gender, women were found to sleep an average of about 18 minutes longer than men.
This study is significant in that consumer wearable devices such as smartwatches are evolving beyond simple health management tools into actual medical research platforms. The research team estimated that sleep measurements from the Samsung Galaxy Watch had an average margin of error of less than 10 minutes when compared with polysomnography, the hospital standard test.
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