Sleeping 7 Hours but Still Tired? Why REM and Deep Sleep Matter for Sleep Quality

Getting seven hours of sleep does not necessarily mean you are getting good-quality sleep. A Thai neurologist highlights growing research showing that sleep duration is only one part of the picture, with sleep stages such as REM and deep sleep also associated with long-term health outcomes.

Assoc. Prof. Dr. Surat Tanprawate, a neurologist and brain specialist at the Faculty of Medicine, Chiang Mai University, recently discussed the importance of sleep quality, noting that while adults are generally advised to get around seven or more hours of sleep, the total number of hours alone does not fully reflect how restorative that sleep may be.

In other words, getting enough sleep and getting good sleep are not necessarily the same thing.

The discussion comes amid growing scientific interest in how different dimensions of sleep  including duration, sleep stages, nighttime awakenings and regularity  may relate to future health.

Study of More Than 95,000 People Examines Sleep and Disease Risk

A large study published in PLOS Medicine analyzed sleep data from more than 95,000 participants in the UK Biobank.

Researchers used wrist-worn devices to assess several characteristics of sleep and followed participants' health for nearly nine years.

The findings suggested that multiple aspects of sleep patterns were associated with the subsequent risk of different diseases. Greater amounts of certain sleep stages, including REM and deep sleep, were associated with lower risks of some health conditions, while very short sleep  particularly less than five hours  was associated with increased risks across a range of conditions.

Importantly, these findings describe associations rather than proving that increasing a particular sleep stage directly prevents disease.

What Is REM Sleep?

REM stands for Rapid Eye Movement, a stage of sleep in which brain activity becomes relatively active and vivid dreaming commonly occurs.

REM sleep is involved in several important neurological processes, including memory consolidation, learning and emotional processing.

In adults, REM sleep commonly accounts for approximately 20 - 25% of total sleep time, although the proportion varies between individuals and across different nights.

For someone sleeping seven to eight hours, this may correspond roughly to 1.5 - 2 hours of REM sleep.

REM periods also tend to become longer during the latter part of the night. This means that regularly cutting sleep short may disproportionately reduce some of the REM-rich sleep that occurs toward morning.

What Is Deep Sleep?

Deep sleep, also known as slow-wave sleep, is the deepest stage of non-REM sleep.

During this stage, heart rate and breathing generally slow, the body becomes more relaxed and it becomes harder to wake up.

Deep sleep is associated with physical restoration and several physiological processes involving the immune system, metabolism and brain recovery.

In adults, deep sleep may account for roughly 10 - 20% of total sleep, although the amount varies considerably depending on age, health and other individual factors. Deep sleep tends to occur more frequently during the earlier part of the night and generally decreases with age.

REM and Deep Sleep Linked to Different Health Outcomes

According to the research discussed by Dr. Surat, greater REM sleep was associated with lower risks of several conditions, including heart failure, atrial fibrillation, ischemic heart disease, dementia, Alzheimer's disease, parkinsonism and multiple sclerosis.

Greater deep sleep was associated with lower risks of conditions including type 2 diabetes, depression, sleep apnea and Parkinson's disease.

However, these findings should not be interpreted as meaning that people should try to maximize REM or deep sleep.

Sleep architecture is naturally regulated by the body and varies according to age, health status, medication use, sleep habits and other physiological factors. A higher percentage of one sleep stage is therefore not automatically better.

Can a Smartwatch Really Measure REM and Deep Sleep?

Consumer wearables have made sleep-stage information increasingly accessible.

Devices such as smartwatches, fitness trackers and smart rings can estimate when users are awake or asleep and may classify periods as light, deep or REM sleep.

However, these devices generally do not directly measure sleep stages in the same way as a clinical sleep study. Instead, they use information such as movement, heart rate and other sensor signals together with algorithms to estimate sleep patterns.

For this reason, wearable sleep data is generally more useful for identifying patterns and trends across multiple nights than for interpreting a single night's REM or deep-sleep number as a medical diagnosis.

People who consistently feel exhausted despite apparently getting enough sleep  particularly those with loud snoring, witnessed pauses in breathing, frequent nighttime awakenings, morning headaches or significant daytime sleepiness  may benefit from discussing their symptoms with a healthcare professional.

How to Support Better Sleep Quality

Healthy sleep is influenced by more than bedtime alone. Maintaining a relatively consistent sleep and wake schedule, exercising regularly and getting natural light during the daytime can help support the body's sleep-wake rhythm.

Reducing caffeine later in the day may also help, while alcohol close to bedtime can disrupt normal sleep architecture even when it initially makes a person feel sleepy.

Getting sufficient total sleep is particularly important for REM sleep because longer REM periods tend to occur later in the night. Deep sleep, meanwhile, may be affected when sleep is repeatedly interrupted.

Ultimately, sleep should not be judged solely by how many hours you spend in bed.

Sleep duration, continuity, regularity and sleep architecture all contribute to the broader picture of sleep health. And if you regularly wake up tired despite apparently sleeping long enough, the issue may deserve more attention than simply adding another hour in bed.

 

Source : Thai Health Promotion Foundation