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The harmful effects of sleep deprivation

man with sleep deprivation holding his hand over his eyes

An audience member sits in a lecture hall and nods off after a bad night's rest. When she opens her eyes, she sees the old coffee stain on her jeans transform into a living creature — yes, a coffee stain creature — and scamper down her leg.

It shuffles around for 10 seconds before it stops moving. Back to a boring old coffee stain.

Stains sprouting legs might sound supernatural, but it was all too real for Whitney Heavner, now a staff scientist at the National Institute of Neurological Disorders and Stroke.

Heavner's lack of sleep had caused a visual hallucination, a surprisingly common side effect of sleep deprivation.

More than a third of American adults don't get enough sleep. By the CDC's guidance, that's anything less than seven hours per night for people over 18.

Short-term effects like confusion and hallucinations usually go away once you're rested. But sleep deprivation and poor sleep habits can also take a serious — sometimes life-threatening — toll on your long-term health.

Decreased eye function

Eyesight needs two main components to work: The eyes and the brain. Sleep affects both, in addition to your eyes' comfort level during the day.

In the short term, sleep deprivation can lead to:

When it comes to long-term eye health, poor sleep can also increase your risk of developing certain eye problems.

These risks, along with others, can be even higher in people who have obstructive sleep apnea, a condition that causes people to stop and start breathing while they sleep.

Nearsightedness (myopia)

Around 34% of people around the world are nearsighted — and counting. Myopia mostly develops during childhood and adolescence, so any efforts to slow it down need to happen during these years.

Sleep deprivation can be particularly harmful to young people's eyesight. One study showed that 12- to 19-year-olds who got fewer than 5 hours of sleep per night were 41% more likely to have myopia than those who got more than 9 hours of sleep per night. Note that this doesn’t mean lack of sleep caused their myopia, but it was correlated with reduced sleep.

Mild nearsightedness rarely causes serious problems, but high myopia can increase the risk of developing serious eye conditions like retinal detachment and macular degeneration.

READ MORE: 12 signs your child might have vision problems


Glaucoma usually happens when fluid pressure inside the eye is too high. The outward pressure damages the optic nerve and leads to permanent vision loss.

Researchers can't say for sure that sleep problems cause glaucoma, but several studies show a connection between the two. One study labeled obstructive sleep apnea as a "major risk factor" for glaucoma.

Another study examined the sleep habits of thousands of people over age 40, all who had glaucoma. People who slept less than three hours, or more than 10 hours, were three times more likely to have optic nerve damage than those who slept around seven hours every night.

Diabetic eye problems

Poor sleep habits may be even more harmful for people who have diabetes.

About 4 million Americans have diabetic retinopathy. This complication of diabetes damages blood vessels inside the eye and can lead to vision loss.

There seems to be a "U-shaped" connection between sleep and diabetic retinopathy (DR):

  • Getting more or less than six to eight hours of sleep increases the risk of developing moderate DR. The further someone gets from this range, the higher the risk.

  • People who get between six and eight hours of sleep are at the lowest risk. Results show the "sweet spot" to be about seven to seven and a half hours of sleep per night.

  • For more serious, vision-threatening retinopathy, the ideal range was between six to seven hours of sleep. Risk increased more quickly with sleep periods over eight hours.

Diabetic men may be at higher risk: When they sleep too much or too little, they're more likely to develop diabetic retinopathy, one study showed. Sleep didn't appear to have the same effect on women, but more information may be needed.

Worsened mental health

Almost 1 in 5 American adults lives with a mental illness. Sleep's effect on mental health isn't always obvious, but the connection is hard to ignore.

Sleep problems are very common in people who have:

  • Anxiety

  • Depression

  • Bipolar disorder

  • ADHD

Patients registered with standard psychiatric practices are about five times more likely to have chronic sleep problems than the overall U.S. population, according to Harvard Health.

In the shorter term, going just 24 hours without sleep can introduce symptoms of psychosis similar to those experienced by people who have schizophrenia. These include hallucinations, delusions and a general disconnect from reality.

Twenty-four hours without sleep might seem like a lot to most people, but you can probably think of at least one time you went 19 or 20 hours (or more) without sleep.

The effects may be temporary, but it shows how fine the line is between healthy sleep and troubling psychological symptoms.

Limited cognitive function

If one set of side effects is most obvious after a sleepless night, it's probably cognitive function.

In general, the term cognitive function is a broad way to refer to the way people:

  • Learn

  • Think

  • Reason

  • Pay attention

  • Remember things

  • Make decisions

  • Solve problems

Sleep has a direct effect on how well the neurons work in your brain. Neurons are the building blocks of the body's nervous system — scientists think there are around 86 billion of them in the brain alone.

Neurons work best when you have plenty of rest (but not too much). Without proper sleep, neurons are out of sync — the split-second neuron assembly lines responsible for thoughts, decisions and feelings are malfunctioning.

That foggy feeling when you try to focus, difficulty remembering what you had for breakfast, a frustratingly short attention span — all of these can happen when your neurons are misfiring.

Researchers have even found that tired driving can be just as dangerous, if not more dangerous, than driving drunk.

These aren't extreme levels of sleepiness, either. In many cases, drivers with a moderate level of fatigue are comparable to drivers over the legal blood-alcohol limit.

Researchers are also getting a clearer view of how poor sleep habits might cause chronic cognitive health conditions.

Several studies have shown a possible link between sleep problems and the risk of developing dementia later in life, including Alzheimer's disease.

One long-term study showed people were 30% more likely to develop dementia if they averaged less than seven hours of sleep per night during their 50s and 60s.

READ MORE: How exercise improves cognitive function

Increased risk of diabetes

Diabetes affects your body's insulin, a natural hormone the pancreas releases to control your blood sugar (glucose). Blood glucose is humans' biggest source of energy.

Diabetes can lead to widespread health effects, especially when it isn't controlled well.

Bad sleep habits can have a two-part effect:

  • They can increase the risk of developing diabetes.

  • They can hurt the body's ability to control blood sugar in someone who already has diabetes.

Poor sleep habits increase the risk of developing type 2 diabetes by increasing the amount of hemoglobin A1c, a protein in your blood. A1c helps transport oxygen throughout your body and is closely tied to blood sugar levels.

People who tend to sleep a little (less than five hours) or a lot (more than nine hours) both had "significantly high" levels of hemoglobin A1c and blood glucose, one study showed.

For people who already have diabetes, getting fewer than seven of hours of sleep can:

  • Make you more resistant to insulin.

  • Increase your blood pressure, and your risk of heart attack as a result.

  • Make it harder for your body to fight infections.

  • Make you feel more hungry and less full after meals.

  • Make you want to eat low-quality foods, especially those high in sugar and carbohydrates.

High blood pressure

Blood pressure is the amount of pressure your blood creates against the walls of your arteries, the blood vessels that move blood from your heart to the rest of your body.

High blood pressure can lead to serious cardiovascular problems, including heart attack, heart failure and stroke.

In healthy people, blood pressure dips between 10% and 20% from their daytime levels while they sleep. Frequent surges higher than this can be bad for cardiovascular health.

In addition to others, several things can affect nighttime blood pressure levels:

  • Getting too little or too much sleep

  • Overall quality of sleep

  • Waking up during the night

  • Dietary factors like salt and alcohol intake

  • Environmental factors like the amount of light or temperature in the room

Conditions like obstructive sleep apnea and nocturia (frequent urination at night) are some of the most common causes of nighttime blood pressure surges.

So if sleep is known to affect short-term blood pressure, can it also cause hypertension (chronic high blood pressure) and heart disease?

Without a doubt, says the CDC.

Sleep deprivation and insomnia are both linked to higher risks of hypertension, one study notes. "Even small increases" in nighttime blood pressure can significantly increase the risk of dying from a cardiovascular problem.

Reduced sleep can lead to weight gain

Sleep deprivation increases ghrelin, the hormone that makes you hungry, and reduces leptin, the satiety hormone. Together, these changes can lead to eating more and gaining weight.

How to prevent these effects

In today's frantic, screen-loaded world, "a good night's rest" is easier said than done. But you can improve your odds of sleeping through the night with these CDC-approved techniques:


  • Make sure your bedroom is dark, quiet and cool. Try keeping the temperature as close to 65 degrees as possible.

  • Don't use any electronic devices in your bedroom.

  • Get some level of physical activity or exercise every day (but not too close to bedtime).

  • Start a routine that helps you unwind before you go to bed. Even simple routines like showering at the same time every night can tell your brain it's time to relax.

  • Get into bed when you're tired — not before then.

Try to avoid:

  • Consuming caffeine less than 8 hours before you plan to go to sleep. For example, if you go to bed at 10 p.m., try to avoid caffeine after 2 p.m.

  • Drinking alcohol in the evening. This can affect your breathing and sleep quality at night.

  • Nicotine, since it's a stimulant like caffeine.

  • Eating meals late at night. This can raise your blood sugar while you rest and hurt the quality of your sleep.

  • Taking naps after 3 p.m.

Around 70 million Americans — 1 in every 5 people — are living with a sleep disorder.

If you regularly have a hard time sleeping or feel tired during the day, talk to your doctor. They may recommend a sleep study to test for sleep-related conditions like sleep apnea, insomnia and restless leg syndrome.

By diagnosing these conditions when they're present, doctors can prescribe treatment that immensely improves the quality of someone's sleep. In some cases, treatment can even be life-saving.

READ NEXT: What do your eyes do while you are sleeping?

Why do humans hallucinate on little sleep? Wu Tsai Neurosciences Institute, Stanford University. February 2016.

Not quite enough: The consequences of sleep deprivation. Stanford Center for Sleep Sciences and Medicine, HuffPost. July 2013.

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