Sleep research usually draws a single line for everyone: less than six hours is a "short" night. A new study from Singapore asks a more personal question. Instead of checking whether you slept under six hours, it checks whether you slept well below your own normal. After tracking hundreds of working adults for up to a year, the researchers found the personal yardstick did a better job of predicting how people felt and functioned the next day.
What the researchers did
The work comes from the Centre for Sleep and Cognition at the National University of Singapore's Yong Loo Lin School of Medicine. First author Chun Siong Soon and senior author Professor Michael Chee published it in the journal Sleep Medicine, and the university announced it on October 5, 2026.
The team followed 462 working adults, mostly university staff, for as long as a year. Each wore an Oura smart ring to record sleep and answered short daily smartphone check-ins about mood, alertness, and motivation. That produced months of nightly data per person, far more than a typical sleep study collects.
For each participant, the researchers worked out what a good night looked like: the 75th percentile of that person's own sleep duration, roughly their longer nights when work and social life got in the way less. A "personal short night" was any night at least one hour below that mark. They then compared this personal definition with the standard under-six-hours rule.
What they found
- Both rules flagged a similar number of nights. About 35% of nights counted as short under the six-hour rule and about 37% under the personal rule. The median personal threshold was 6.1 hours, so on average the two lines sat close together.
- The personal rule tracked next-day effects more closely. Personal short nights showed bigger associations with lower alertness, sleep satisfaction, and motivation, and with higher stress and sadness. They also showed bigger associations with sleeping heart rate, heart-rate variability, and how active or sedentary people were the next day.
- Back-to-back short nights added up. Effects grew with each consecutive short night. Alertness, for example, fell by about one point on a 100-point scale for every additional night in a row.
- Most short nights were one-offs. For 86.4% of participants, the typical run of short sleep lasted just one night.
- Catch-up sleep was modest. After a short weeknight, people slept about 50 minutes longer the following night. Weekends allowed more recovery, but only up to about an hour and 15 minutes.
- A link to heart health appeared. Blood pressure, artery stiffness, and waist-to-height ratio were measured once, when people joined. Participants with a larger share of personal short nights tended to have higher readings on all three. Each 10-percentage-point increase was associated with about 1.5 points higher systolic (top-number) blood pressure.
The team also ran a secondary analysis of anonymized data from 376,758 Oura users in seven countries: Australia, Finland, Germany, Japan, Singapore, the United Kingdom, and the United States. Typical sleep differed by country, but the overall patterns held up.
Why a personal yardstick makes sense
The six-hour line is a population average, and people vary. Someone who normally sleeps eight and a half hours and gets six is running well short of their usual. A person who reliably sleeps six and a half and gets six has lost much less. The fixed rule treats both nights the same. The personal rule treats the first one as the bigger deficit, and the mood and alertness data suggest that's closer to how people actually experience it.
Professor Chee put it this way: population thresholds remain useful, but once you have months of data on one person, you can ask when that person is sleeping substantially less than is usual for them. Until recently that question was impractical outside a lab. Wearables that people keep on for months make it answerable.
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Our free Sleep Schedule Builder helps you plan consistent bed and wake times that fit your life, so short nights become the exception rather than the pattern.
The caveats
- Your usual sleep isn't the same as your sleep need. The authors stress that the personal threshold reflects how much people actually slept, which depends on opportunity and life demands, not a measure of how much sleep their body requires. If you've been chronically short for years, your "normal" may already be too little.
- It's observational. The study shows associations. It can't prove that short nights caused the lower mood or higher blood pressure. The heart measurements were taken only once.
- The group was narrow. Most participants were relatively healthy staff at one university, so the results may not apply to people with chronic illness or sleep disorders.
- Consumer devices estimate sleep. A smart ring is good at tracking sleep duration over time but isn't a clinical sleep test. NUS also runs a joint research lab with Oura, the ring's maker, which is worth knowing when reading wearable research from the group.
How to use this yourself
You don't need a year of ring data to borrow the idea. A few practical steps:
- Find your baseline. Use a tracker or a simple sleep diary for two or three weeks, and pay most attention to nights when you went to bed on time and woke without rushing. That's a rough picture of your better nights.
- Treat an hour below that as a warning sign. One short night is common and usually recovers on its own. Several in a row is where this study saw mood and alertness slide most.
- Don't count on weekends to fix a deficit. Recovery sleep here topped out around an hour and a quarter. Our earlier look at weekend catch-up sleep and blood pressure found a similar story: a little helps, a lot backfires.
- Keep the floor in mind. A personal baseline doesn't replace general guidance. The American Academy of Sleep Medicine recommends at least 7 hours a night for adults. If your baseline is well below that and you feel tired all the time, the baseline itself may be the problem.
Key takeaways
- An NUS study of 462 working adults tracked with Oura rings for up to a year defined short sleep as one hour below each person's own better nights.
- That personal definition flagged about as many nights as the six-hour rule (37% vs. 35%) but was more closely linked to next-day alertness, mood, stress, and motivation.
- Effects grew with consecutive short nights, and catch-up sleep was limited to about 50 minutes on weeknights and about 75 minutes on weekends.
- More frequent personal short nights were associated with higher blood pressure and stiffer arteries, though the study can't show cause and effect.
- Your usual sleep is a useful benchmark, but it's not proof of what your body needs. Pair it with the 7-hour minimum for adults.
The bigger shift here is in how sleep is measured. For decades, research has had to judge everyone against one cutoff. With months of nightly data, it's becoming possible to ask a more useful question: not "did you sleep six hours?" but "did you get the sleep you normally get?" For most people, the practical answer is the same one sleep experts keep coming back to: a steady schedule that rarely strings short nights together.
Source: EurekAlert! (news release from the National University of Singapore, Yong Loo Lin School of Medicine) — "How short is too short? Long-term wearable data point to a more personal way of defining insufficient sleep," October 5, 2026, https://www.eurekalert.org/news-releases/1146599. Study: Soon C.S., Chee M.W.L. et al., Sleep Medicine, 2026, doi:10.1016/j.sleep.2026.109294.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. The research described is observational and does not show that short sleep caused the outcomes reported. If you have ongoing sleep problems, daytime sleepiness, or high blood pressure, talk to a qualified healthcare provider.
About Better Night Sleep: Better Night Sleep is an independent sleep-education and product-research resource. Our articles are written and edited by the Better Night Sleep editorial team using reputable public sources and established sleep-health recommendations. Learn more about us.