Is 5 Hours of Sleep Enough? The Truth According to Science

In today’s fast-paced, always-on world, sleep often becomes a casualty of ambition, parenting, work stress, or late-night screen time. Many people get by on 5 hours and ask: Is 5 hours of sleep enough? 

The blunt answer: for the overwhelming majority of people, no, it is not.

This article explores what happens when adults regularly sleep only 5 hours, what the science says about its impact, and whether there are rare exceptions to the rule.

What Happens to Your Body with Only 5 Hours of Sleep?

Getting just 5 hours of sleep per night—even for a few days—causes measurable declines in cognitive and physical performance.

Documented effects include:

• Slower reaction times (comparable to drink-driving)

• Impaired decision-making

• Mood swings and irritability

• Higher cortisol (stress hormone) levels

• Reduced immune function

A study by the University of Pennsylvania (Van Dongen et al., 2003) found that individuals restricted to 4–6 hours of sleep over two weeks performed as badly on cognitive tests as those kept awake for 48 hours straight.

Can Some People Function on 5 Hours?

There is a rare gene mutation called DEC2, found in less than 1% of the population, which allows those individuals to function well on just 4–6 hours of sleep. These are known as natural short sleepers.

However, for nearly everyone else, functioning on 5 hours is a case of survival, not thriving. The brain and body begin to accumulate sleep debt, which doesn’t go unnoticed by the nervous system, even if the individual "feels fine."

Sleep Cycles: Why 5 Hours Misses the Mark

A complete sleep cycle takes roughly 90 minutes, and adults typically need 5–6 cycles per night. With 5 hours of sleep, that’s just 3 cycles, which means:

• Incomplete REM sleep (critical for memory and emotional regulation)

• Insufficient deep sleep (vital for recovery and hormonal balance)

• Increased likelihood of waking during light sleep phases, causing grogginess

Mental Health Risks from 5-Hour Sleep Patterns

Sleep deprivation is a well-documented risk factor for mental health conditions. A study in The Lancet Psychiatry (Walker & van der Helm, 2009) found that lack of REM sleep, more likely when sleep is restricted to 5 hours, can lead to increased anxiety and emotional dysregulation.

Mood, motivation, and resilience to stress all take a hit when sleep is consistently inadequate.

The Long-Term Impact of Sleeping 5 Hours a Night

While some people get used to a 5-hour sleep schedule, research shows that the long-term risks increase over time. Chronic sleep restriction has been linked to:

• Increased risk of stroke

• Hypertension (high blood pressure)

• Impaired glucose tolerance and insulin resistance

• Neurodegeneration and memory loss

The Whitehall II study, one of the largest long-term studies on British civil servants, found that those who reduced their sleep from 7 to 5 hours were at a significantly higher risk of developing chronic illness.

Does Sleep Quality Make Up for Short Duration?

High-quality sleep can help, but only partially. A study in PLOS ONE (Lo et al., 2016) found that fragmented sleep, even if long, resulted in impaired cognitive function compared to shorter, uninterrupted sleep. However, 5 hours is not enough time to reach sufficient REM and deep sleep, even if it’s good quality.

Sleep quality matters, but sleep quantity is still crucial.

What If 5 Hours Is All You Can Get?

Sometimes life gets in the way. If 5 hours is all that’s available:

• Nap when possible (ideally 20–30 mins or a full 90-minute cycle)

• Stick to a regular schedule to help the body adapt

• Avoid caffeine after midday

• Focus on improving sleep hygiene (dark room, no screens before bed, calm wind-down routine)

But these are temporary workarounds—not solutions.

Expert Views on Sleeping Five Hours

Shelby Harris, Psy.D., and clinical psychologist specialising in behavioural sleep medicine and Director of Sleep Health at Sleepopolis, told Today.com:

"Five hours is just too little sleep, especially if you’re doing it routinely"

Conclusion: Is 5 Hours of Sleep Enough?

For almost all adults, no — 5 hours of sleep is not enough. While there may be rare exceptions due to genetics, most people need at least 7 hours per night for optimal physical health, mental clarity, and emotional stability.

Even if you don’t feel the effects immediately, sleep debt builds up quietly in the background, influencing everything from heart health to hormone regulation.

Prioritising sleep isn’t indulgent — it’s essential. If 5 hours is the norm, not the exception, it may be time to re-evaluate work habits, screen time, and evening routines.

Related: Is 6 hours of sleep enough?

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Frequently Asked Questions

Is 5 hours of sleep enough for adults?

For the vast majority of adults, no. The NHS recommends 7–9 hours of sleep per night. Regularly sleeping only 5 hours is associated with impaired cognitive performance, increased risk of chronic illness, and long-term mental health concerns.

Can I train my body to function on 5 hours of sleep?

Are there people who naturally need less sleep?

Is it better to sleep 5 hours straight or take naps?

What if I feel fine on 5 hours of sleep?