Sure, sleep deprivation can leave you feeling grumpy, listless, and unable to focus, but did you know that lack of sleep disrupts every physiological function in the body and that it could seriously harm your health?
Under strict experimental conditions, even short-term sleep deprivation produces a variety of adverse physiological effects, including high blood pressure, activation of the sympathetic nervous system, impairment of blood sugar control, and increased inflammation. A variety of epidemiological studies have also suggested an association between sleep duration and long-term health.
Chronic sleep deprivation has been implicated in the development of a number of illnesses and conditions, including high blood pressure and heart disease, obesity, diabetes, immune system problems, as well as poor performance in school, in the workplace, and during sports. Chronic sleep loss may also contribute to acceleration of the aging process.
Sleep serves as an indicator of physical and mental health and quality of life. Insufficient sleep is associated with poor decision-making, impaired judgment, and poor coordination, as well as increased risk-taking and delayed reaction time. All of these problems translate into serious safety risks such as impaired driving, car accidents, and other kinds of errors. Sleep deprivation can trigger or exacerbate anxiety, depression, and other emotional problems, and it can heighten the symptoms of disorders involving concentration and impulse control such as attention deficit hyperactivity disorder (ADHD).
Lack of sleep, whether short-term sleep loss or chronic deprivation, can have a serious impact on cardiovascular health. Both blood pressure and heart rate increase following sleep-deprived nights.
Sleeping less than five or six hours per night has been linked to increased risk for high blood pressure. One study of subjects between the ages of thirty-two and fifty-nine found that sleeping less than five hours per night was associated with more than double the risk for high blood pressure. Other research has confirmed that men who sleep five hours or less a night suffer twice as many heart attacks as men who sleep eight hours or longer.
Sleep deprivation also increases the risk of heart disease in women. Women who sleep less than five hours a night have a 30 percent higher risk of developing coronary heart disease than those who sleep eight hours or longer. Although studies have also found that oversleeping is associated with a greater risk of heart disease, many researchers speculate that oversleeping is actually an indicator of other illnesses that increase risk for heart disease—such as such as sleep apnea—rather than a risk factor.
When researchers discovered that shift workers who work through the night were unusually prone to breast and colon cancer, they identified one possible explanation: exposure to light at night reduces levels of the hormone melatonin, which the brain produces during sleep. Melatonin—an antioxidant that helps to counter the damage caused by free-radical compounds, including cancer-causing mutations—is also thought to protect against cancer by affecting levels of other hormones, such as estrogen.
Melatonin can prevent tumor cells from growing and slows the production of estrogen by the ovaries. In many cases of ovarian and breast cancer, estrogen stimulates the cancerous cells to continue dividing. Researchers hypothesize that people who are up late at night or get up frequently in the night on average produce less melatonin, which in turn means that more cancer-activating estrogen is circulating throughout their bodies.
Another by-product of sleep deprivation is a shifted cortisol rhythm. Cortisol usually peaks at dawn and declines throughout the day. Since cortisol helps to regulate immune system activity, including the activity of a group of immune cells called natural-killer cells (NK cells) that help to combat cancer, people whose cortisol cycle is disrupted by troubled sleep may be more likely to develop cancer.
Research reveals that chronically sleep-deprived people tend to develop problems regulating their blood sugar, which may increase their risk for diabetes. Studies also have demonstrated that sleep deprivation in healthy men results in disturbances of glucose metabolism.
Even healthy young adults who regularly get by on just five hours of sleep a night have to secrete 30% more insulin to regulate their blood glucose levels than their peers who sleep eight hours or longer.
Many studies have confirmed a clear and direct relationship between sleep duration and insulin sensitivity—the capacity to respond to insulin-stimulated glucose uptake following consumption of carbohydrates. Short sleepers have lower insulin sensitivity, and longer sleepers have higher insulin sensitivity.
Immune System Functions
Sleep has powerful effects on immune function. Sleep deprivation has been shown to alter immune responses and to increase circulating blood levels of inflammatory markers with measurable and significant elevations after only one night of sleep loss.
The good news is that once sleep is recovered, the immune system seems to easily rebound. It’s reasonable to suggest that improving sleep could potentially reduce inflammation and, by doing so, reduce the risk for inflammatory diseases.
Sleep also plays an important role in supporting adaptive cellular immune responses, which suggests that improving sleep could potentially be an important additional treatment for certain immunological disorders and enhance the benefits of immunization.
Could Sleep Loss = Weight Gain?
Recent research reveals that sleep duration is related to weight gain. People who sleep the least appear to be the most likely to gain weight and to become overweight and obese, possibly because their sleep debts make them less able to control hunger and recognize satiety.
Even mild sleep deprivation quickly disrupts normal levels of serotonin, as well as leptin and ghrelin, the hormones that regulate appetite and satiety.
Sleep deprivation leads to decreased levels of the satiety hormone leptin, increased levels of the hunger hormone ghrelin, and impaired glucose tolerance. Volunteers subjected to partial sleep deprivation reported that their appetites increased, and researchers observed a high level of correlation between the subjects’ assessments of their appetites and an increase in their ghrelin to leptin ratios.
Learning and Memory
It’s easy to understand how sleep deprivation can seriously compromise your ability to learn. Sleepy people have trouble concentrating, their minds wander, and their response times slow. Lack of sleep reduces the ability to pay attention and slows the ability to think and react quickly, while increasing the likelihood of making mistakes. When we perform tasks after a few nights of sleeplessness, slower response times, fatigability (the deterioration of performance over time), impaired thinking, reduced learning, and short-term recall can be expected.
As discussed earlier memory—the retention of material that has been learned—is necessary in order for learning to occur. Memory involves the creation, use, and maintenance of strong networks of brain cells. Researchers report that areas of the brain activated during daytime learning were reactivated during sleep. Apparently, sleep is the brain’s way of managing the connections, boosting some while reducing others. With reduced sleep, the brain doesn’t have time to properly restore neural connections.
Mental Health and Emotional Well-being
There is no question that sleep deprivation has a profound effect on mood and mental health. And it’s much more than waking up bleary-eyed or feeling grumpy or irritated. There is a strong association between sleep loss and depression, anxiety, and other mental health problems. It’s not surprising that sleep deprivation affects mood and mental health when you consider that sleep involves a shift in the balance of the same neurotransmitters—serotonin, norepinephrine, dopamine, melatonin, and others—involved in governing cognition and emotional well-being.
Although the precise relationship between sleep and mental health has not yet been uncovered, one possible explanation is that conditions such as sleep apnea may contribute to mood disorders by depriving the brain of oxygen. Another way that sleep helps us to maintain optimal emotional and social functioning is by allowing the parts of the brain that control emotions and social interactions to rest while we sleep.
Sleep deprivation also may cloud moral judgment. Recent research found that following two sleepless nights, volunteer subjects displayed compromised ability to make decisions when presented with emotionally charged moral dilemmas.
Sleep and Sex
Conventional wisdom holds that participating in sexual activity promotes good, sound sleep and it is believed that sexual activity increases the need to sleep in many species. Among humans it is thought to induce sleep by inducing muscle relaxation, relieving stress and tension, and flooding the brain and body with the neurochemicals associated with pleasure, tranquility, and satisfaction. Anxieties and inhibitions tend to dissolve into feelings of emotional warmth, well being, and pleasant drowsiness.
Safety and Accidents
One of the scariest findings from sleep research laboratories is that reducing sleep time in healthy adults to between four and six hours per night produces cumulative increases in daytime performance deficits. These can become so severe that ultimately, they reach levels comparable to the deficits found under conditions of acute total sleep deprivation—all without the affected person feeling extremely sleepy. This finding, that sleep loss affects cognitive speed and accuracy, memory, and reaction time without the sleep-deprived person being aware of the deficits, suggests that the brain is vulnerable to chronically reduced sleep in a way that is not fully apparent in the subjective perception and assessment of sleepiness.
Workplace drowsiness is recognized as a major cause of industrial and personal-injury accidents, compromised productivity, and even deaths. According to the National Sleep Foundation (NSF), the overwhelming majority of Americans believe that inadequate sleep impairs their work performance and puts them at increased risk for accidents, injuries, and health problems.
The bottom line? Get more sleep. In spite of needing to pull all-nighters for school and wanting to stay up late on the weekends, it simply isn’t worth it. You have one body, and one body only, and it’s wise to treat it with the care that it needs to live a happy, healthful life.