Sleep is tied to every organ system in the body. So if you deprive your body of it, it won’t function properly. It’s not just about the total amount; it’s also about the stages of sleep.

Each of the phases, REM (usually 25 percent of the total night) and NON-REM, need to be present to a certain percent in order to have restful sleep, Dr. Michael Marino, Medical Director of Geisinger Sleep Labs, says.

What people who don’t get enough sleep should do is write down they typical days, Dr. Marino says. That includes work, meals, exercise, and bedtime. “Then we’d look at their sleep hours and see what we can improve,” he adds. “Priorities will have to be set."

That’s not a good thing, though, Dr. Marino says. The body learns to tolerate functioning tired but that doesn’t change the fact that chronic sleep deprivation will take a toll eventually, he adds.  You’re still going to pay a price.

There is an overlap of patients with insufficient sleep and an increased perception of pain, Dr. Marino says. “Mild pain becomes more severe.” So poor sleep increases the perception of pain, and that becomes a reason for not being able to fall asleep.

This is a very common emotional reaction to sleep deprivation, Dr. Marino says. “It’s the general sensation of fatigue – you can’t get any tasks done.” Mood swings are not uncommon. Chronic sleep deprivation has been linked to anxiety disorders, according to the Anxiety and Depression Association of America.

A study found that subjects who were limited to only 4.5 hours of sleep a night for one week reported feeling more stressed, angry, sad, and mentally exhausted. When the participants resumed normal sleep, they reported a significant improvement in mood.

Lack of adequate and enough sleep feeds depression and anxiety. Evidence suggests that people with insomnia have a ten-fold risk of developing depression compared with those who sleep well. Obstructive sleep apnea (OSA) is also linked with depression. In a study people with the illness were found to be five times more likely to suffer from OSA.

Your body won’t burn calories as well and you gain weight, Dr. Marino says. Chronic sleep loss can reduce the capacity of even young adults to perform basic metabolic functions such as processing and storing carbohydrates or regulating hormone secretion, according to a study.

Sleep deprivation affects the brain in a way that makes you want to eat more and not process food efficiently. It sparks a vicious cycle where you are left feeling tired, slowing your metabolism and playing tricks with your hormones. Research has shown a connection between short sleep duration and elevated levels of ghrelin, which is commonly known as the “hunger hormone.” Food choices are significantly associated with sleep duration, studies show. Short sleepers tend to drink less water and eat fewer fruits and vegetables than people who have normal and consistent sleep patterns. 

Why do you think athletes stress the importance of going to bed early? Chronic sleep deprivation can hinder your overall athletic performance in the long-term. The longer period of time without you getting enough rest, the more your reflexive time will decrease. Even snooze time will improve performance, a study shows. Sleep deprivation also decreases the production of glycogen which is stored for energy use during exercise.

The body rests and repairs itself during sleep, so when you haven’t given it enough hours of what it needs the risk of rundown and general malaise increase, Dr. Marino says. This is different than getting physically sick, the chances for which also increase.

Sleep is crucial to prevent the cold, flu and other infections, doctors say. Past Sleep in America polls conducted by the National Sleep Foundation indicate that children and the elderly, identified as high-risk populations and first in line for the flu vaccine, are often sleep-deprived. You need restorative sleep to get the body back into disease-fighting shape, according to studies.

Lack of sleep harms cognitive function. Thinking becomes harder as research has shown. A sleep-deprived person cannot focus attention optimally, and, therefore, cannot learn efficiently because receiving new information becomes more difficult.

Consolidation of the memory occurs during sleep. Without adequate sleep and rest, over-worked neurons can no longer function to coordinate information properly, leading to the loss of ability to access previously learned information, according to studies.

Lack of REM sleep increase the risk of developing Alzheimer’s disease, Dr. Marino says. The reason is the cerebral spinal fluid, which serves as a cleaning agent for the brain. It flushes the toxins that build up when people are awake, Dr. Marino adds.  It is more effective during REM sleep.

If you’re on little sleep, the fat cells’ ability to react properly to insulin (the hormone that regulates energy storage) decreases by 30 percent.  Such chronic disruption could cause weight gain, type 2 diabetes and other health problems, according to a study.

Sleep deprivation can create insulin resistance (reduced insulin sensitivity) and make it worse, Dr. Marino says. Diabetics who can’t sleep may require medication, he adds.

Less sleep leads to higher blood pressure because of the body is working harder to produce cortisol, also known as the “stress hormone.” As your insulin level rises, your blood pressure rises. A study has shown that shorter sleep actually worsens hypertension. Research has indicated that people with hypertension suffer the effects of even one night without enough shuteye hours.

There is a direct correlation between high blood pressure and blood flow blockage, Dr. Marino says. When people are under stress, cytokines, which are chemicals that cause inflammation of the blood vessels, build up, he adds. Plaque can rupture causing the tissue to no longer receive oxygen.

“We know there is a risk of recurrence in sleep-deprived patients,” Dr. Marino says. There is no primary prevention data, studies are still in the works, he adds. There is experimental and observational evidence showing a strong association between short/long sleep durations and higher risk of stroke.

Studies have calculated that undersleepers, and oversleepers for that matter, are mentally two years older than those who got 7-8 hours of shuteye a night. Also, lack of sleep causes dark circles under your eyes, which makes you look tired, and speed up the aging process.

“Beauty sleep” is a real thing, Dr. Marino agrees. The cause and effect is a complex matter but the body, and that includes one’s skin, requires time to recover. “Sleep time is when the body attends to that,” Dr. Marino says. The skin has its own circadian rhythm, which controls cell growth and renewal of multiple physiological systems. A study found that adults who didn’t get enough sleep were much more likely to be unhappy with the way they look because they noticed more wrinkles, fine lines, and age spots.

FES is known to be associated with obesity, obstructive sleep apnea, Dr. Marino says, among other conditions. The eyelids become loose and rubbery as a result of the chronic flipping during sleep.

A micro-sleep is an uncontrollable and temporary episode of sleep that may last for a few seconds. “You are either awake or asleep,” Dr. Marino says. The body is not programmed for micro sleeps, he adds. This very short kind of sleep is not restorative.

Studies in recent years have identified a relationship between lack of sleep and some of the top cancers in the U.S. – breast, prostate, and colorectal cancers, according to the Cancer Treatment Centers of America. Research suggests that people who have sleep apnea have an increased risk of developing any type of cancer. A separate  study  found that men who suffer from insomnia may be at increased risk of prostate cancer.

Sex hormones drop as much as 15 percent in men who have slept fewer than five hours, according to research. Sleep apnea has also been linked to lower levels of testosterone, according to studies. This is due to the fact that lack of sleep leads to people lacking energy. Separate research found that every extra hour of sleep made women 14 percent more likely to engage in sexual activity.

Getting behind the wheel when you are tired is a huge mistake. According to WebMD, “sleep deprivation was a factor in some of the biggest disasters in recent history: the 1979 nuclear accident at Three Mile Island, the massive Exxon Valdez oil spill, the 1986 nuclear meltdown at Chernobyl, and others."