How many hours of sleep did you get last night? If you regularly sleep nine hours or more, two significant studies should catch your attention.
A 30-year Taiwanese investigation following more than 3,000 people found that consistently sleeping beyond nine hours was associated with a higher all-cause mortality risk compared with seven to eight hours.
A separate meta-analysis involving more than 2.1 million people found a similar pattern, with stronger associations at both ends of the sleep spectrum. Together, the findings have renewed attention around sleep duration as a possible health signal.
The research points to a relationship researchers are still working to understand; one that may reveal more about underlying health than the hours spent in bed alone.
What the Thirty-Year Taiwanese Study Actually Found
The numbers behind the study are worth understanding before drawing any conclusions about your own nightly routine.
Researchers in the Journal of Sleep Research compared outcomes across different sleep groups and found that people sleeping seven to eight hours had the lowest mortality rate: 10.57 deaths per 1,000 people. Those sleeping fewer than six hours recorded 10.97 deaths per 1,000, while those regularly sleeping more than nine hours reached 11.27.
That difference translated to a 17% higher all-cause mortality association for the long-sleep group compared with the seven-to-eight-hour group. The standard recommendation for adults remains seven to nine hours of sleep per night, placing the study’s lowest-mortality category toward the lower end of that range.
Blood pressure appeared to explain part of the connection, but not all of it. The researchers noted that “blood pressure accounted for a modest proportion of this association.” That leaves a larger question unanswered: what other factors may link longer sleep duration with health outcomes?
Nine Hours of Sleep Might Be a Signal, Not the Problem
The most important detail the researchers shared is not the mortality figure. It’s that the study identified an association, not a cause.
The study did not prove that sleeping more than nine hours increases mortality risk. Instead, long sleep may reflect something already affecting a person’s health, such as an undiagnosed condition or other factors.
The researchers considered possible explanations including blood pressure, inflammation, circadian disruption, and hormonal regulation, but none was confirmed. That distinction matters because an occasional long sleep after a demanding week differs greatly from a persistent pattern.
They suggested that sleep duration could eventually become part of routine health conversations, similar to other basic measurements. The focus is not on cutting sleep but on noticing patterns, especially when long sleep appears alongside ongoing tiredness or other changes.
Related: 5 Things You Should Never Wear Before Sleeping
How 2.1 Million People Changed the Picture
The Taiwanese study provided a compelling data point. Researchers at Semmelweis University in Budapest built something considerably larger in 2025 to examine it.
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The Semmelweis team combined results from 79 international publications involving more than 2.1 million people. Their analysis examined both shorter and longer sleep durations and found that regularly sleeping fewer than seven hours was linked to a 14% higher all-cause mortality risk than sleeping seven to eight hours.
For those sleeping nine or more hours, the association reached 34%. These findings come from a separate research pool and should not replace the Taiwanese study’s 17% figure. Instead, the two studies point in a similar direction across different datasets.
The analysis also found differences by sex. Men sleeping eight or more hours showed a 36% increased mortality risk, while women with long habitual sleep showed a 44% increase. Researchers noted that the reasons behind those differences remain unclear, with hormonal, behavioral, and cardiovascular factors among possible explanations.
Screens, Stress and What Semmelweis Calls a Sleep Epidemic
Before anyone reaches for a sleep tracker, the Semmelweis researchers want to name what’s disrupting sleep in the first place.
The researchers pointed to several modern pressures affecting sleep, including blue-light exposure, constant work demands, stress, and expectations of being available around the clock. They describe these influences as contributing to a “sleep epidemic.”
Shift workers and people with irregular schedules face particular challenges, but the researchers noted that sleep disruption extends beyond those groups.
Semmelweis recommends maintaining consistent sleep schedules, reducing screen use before bed, keeping bedrooms dark and quiet, and limiting late alcohol and caffeine. Those recommendations come from broader sleep guidance rather than direct findings from the mortality and stroke studies.
What Long Sleepers Should Actually Take From This
None of this research calls for deliberately sleeping less. What it calls for is attention.
The studies suggest that habitual sleep duration may provide useful information during health check-ups. If sleeping nine or more hours has become a regular pattern, especially when it comes with persistent fatigue or other health changes, it may be worth discussing with a doctor.
The larger question remains unresolved: does long sleep itself influence health outcomes, or is it mainly a sign of something else happening in the body? Both research groups found a consistent association, but the mechanism behind it is still being studied.
For now, the message is not that a longer night of sleep is automatically harmful. It is that sleep patterns may contain clues, and those clues may deserve more attention than they have traditionally received.
If your doctor began asking about your average nightly sleep hours at every check-up, would you think it was worth the conversation?
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