Think You’re Sleeping Enough? It’s Not Just About the Hours

Getting enough sleep matters, but simply counting the hours may not tell you how well you are actually sleeping.

A major new study suggests that different aspects of sleep, including time spent in REM and deep sleep, how often you wake during the night, and how consistent your sleep is from one night to the next, are associated with future health. The findings suggest that when it comes to sleep, quality and regularity may matter alongside quantity.

Researchers analyzed data from 95,559 participants in the UK Biobank. Participants wore wrist accelerometers continuously for seven days and nights, and a deep-learning algorithm was used to estimate their sleep stages, total sleep duration, time awake after falling asleep, and night-to-night irregularity.

Researchers then followed participants for a median of 8.9 years, examining associations between these sleep patterns and 1,049 health outcomes.

REM Sleep Was Linked to Dozens of Health Conditions

One of the most striking findings involved REM sleep, the stage strongly associated with dreaming.

An additional 47.6 minutes of estimated REM sleep, representing the difference between the lower and upper quarters of REM duration in the study, was associated with a lower risk of 83 conditions across 12 disease categories.

Among the associations were heart failure, atrial fibrillation, dementia, Alzheimer’s disease, multiple sclerosis, and parkinsonism.

For example, the hazard ratio associated with this difference in REM sleep was 0.74 for heart failure, 0.54 for dementia, and 0.20 for parkinsonism. A hazard ratio below 1 indicates that the condition occurred less often during follow-up among participants with more estimated REM sleep.

But these numbers need to be interpreted carefully.

The study was observational, meaning it can identify associations but cannot prove that getting more REM sleep directly prevents these diseases. Poor or changing sleep may also be an early sign of an underlying health problem that has not yet been diagnosed.

There is another important limitation: participants did not undergo overnight sleep studies. Their sleep stages were estimated from wrist accelerometer data using a deep-learning algorithm. The researchers also based their analysis on one week of sleep monitoring, which may not perfectly represent a person’s long-term sleeping habits.

Deep Sleep and Regular Sleep Matter Too

REM was not the only stage associated with health.

Greater estimated deep sleep, measured per approximately 47.5-minute increase, was associated with a lower risk of seven conditions across five categories, including type 2 diabetes and major depressive disorder.

Researchers also found that greater sleep irregularity and spending more time awake after initially falling asleep were associated with higher risks of several conditions.

Total sleep duration mattered as well, although the relationship was not as simple as “more is always better.”

For 69 health outcomes, the lowest-risk sleep durations were predominantly concentrated between six and eight hours a night. Meanwhile, sleeping fewer than five hours was associated with increased risk for 37 conditions compared with the six-to-eight-hour reference group.

That does not mean everyone should aim for precisely the same number of hours. Individual sleep needs vary, and other research and clinical guidelines may recommend different amounts depending on factors such as age.

Good Sleep Is About More Than the Clock

The study adds to growing evidence that healthy sleep is multidimensional. How long you sleep matters, but so may the structure, continuity, and regularity of that sleep.

Rather than becoming preoccupied with achieving a particular number of minutes of REM or deep sleep on a wearable device, the more practical goal is to support healthy sleep overall: maintain a reasonably consistent schedule, allow yourself enough time to sleep, and pay attention to persistent problems such as frequent awakenings or significant daytime fatigue.

Anyone regularly experiencing very short sleep, repeated nighttime awakenings, excessive daytime sleepiness, or other significant changes in sleep should consider discussing them with a healthcare professional.

After all, a night of sleep cannot necessarily be judged by one number on the clock. How you sleep may matter just as much as how long.