The Hidden Costs of Insufficient Sleep
Sleep is often one of the first things to go when people feel pressed for time. Many view sleep as a luxury and think that the benefits of limiting the hours they spend asleep outweigh the costs. People often overlook the potential long-term health consequences of insufficient sleep, and the impact that health problems can ultimately have on one’s time and productivity.
Sleep and Health
- It can be tempting to trade sleep for a few precious hours of wakefulness, but it is important to consider the hidden costs. Sleep is precious, too.
- Numerous studies have found that insufficient sleep increases a person’s risk of developing serious medical conditions, including obesity, diabetes, and cardiovascular disease.
- Lack of adequate sleep over time has been associated with a shortened lifespan.
Not getting enough sleep alters insulin resistance, which is associated with an increased risk of developing type 2 diabetes, and that can be very quickly induced by a single night’s total sleep loss – Dr. Ann E. Rogers
Many of the costs of poor sleep go unnoticed. Medical conditions, such as obesity, diabetes, and cardiovascular disease, develop over long periods of time and result from a number of factors, such as genetics, poor nutrition, and lack of exercise. Insufficient sleep has also been linked to these and other health problems, and is considered an important risk factor. Although scientists have just begun to identify the connections between insufficient sleep and disease, most experts have concluded that getting enough high-quality sleep may be as important to health and well-being as nutrition and exercise.
Determining the risks posed by insufficient sleep is complicated. Medical conditions are slow to develop and have multiple risk factors connected to them. What we do know is that sleeping fewer than about eight hours per night on a regular basis seems to increase the risk of developing a number of medical conditions. The study results below show that reducing sleep by just two or three hours per night can have dramatic health consequences.
- Obesity—Several studies have linked insufficient sleep and weight gain. For example, one study found that people who slept fewer than six hours per night on a regular basis were much more likely to have excess body weight, while people who slept an average of eight hours per night had the lowest relative body fat of the study group. Another study found that babies who are “short sleepers” are much more likely to develop obesity later in childhood than those who sleep the recommended amount.
- Diabetes—Studies have shown that people who reported sleeping fewer than five hours per night had a greatly increased risk of having or developing type 2 diabetes.3,4 Fortunately, studies have also found that improved sleep can positively influence blood sugar control and reduce the effects of type 2 diabetes.
- Cardiovascular disease and hypertension—A recent study found that even modestly reduced sleep (six to seven hours per night) was associated with a greatly increased the risk of coronary artery calcification, a predictor of future myocardial infarction (heart attack) and death due to heart disease.6 There is also growing evidence of a connection between sleep loss caused by obstructive sleep apnea and an increased risk of cardiovascular diseases, including hypertension, stroke, coronary heart disease, and irregular heartbeat.
- Immune function—Interactions between sleep and the immune system have been well documented. Sleep deprivation increases the levels of many inflammatory mediators, and infections in turn affect the amount and patterns of sleep.8 While scientists are just beginning to understand these interactions, early work suggests that sleep deprivation may decrease the ability to resist infection (see The Common Cold, below).
- Common Cold – In a recent study, people who averaged less than seven hours of sleep a night were about three times more likely to develop cold symptoms than study volunteers who got eight or more hours of sleep when exposed to the cold-causing rhinovirus. In addition, those individuals who got better quality sleep were the least likely to come down with a cold.
Not surprisingly, these potential adverse health effects can add up to increased health care costs and decreased productivity. More importantly, insufficient sleep can ultimately affect life expectancy and day-to-day well-being. An analysis of data from three separate studies suggests that sleeping five or fewer hours per night may increase mortality risk by as much as 15 percent.
Sleeping Well, Staying Healthy
While sleeping well is no guarantee of good health, it does help to maintain many vital functions. One of the most important of these functions may be to provide cells and tissues with the opportunity to recover from the wear and tear of daily life. Major restorative functions in the body such as tissue repair, muscle growth, and protein synthesis occur almost exclusively during sleep.
Many other conclusions about the role sleep plays in maintaining health have come from studying what happens when humans and other animals are deprived of the sleep they need. For example, scientists have discovered that insufficient sleep may cause health problems by altering levels of the hormones involved in such processes as metabolism, appetite regulation, and stress response.11,12,13 Studies such as these may one day lead to a better understanding of how insufficient sleep increases disease risk.
In the meantime, sleep experts say there is ample evidence that shows that when people get the sleep they need, they will not only feel better, but will also increase their odds of living healthier, more productive lives.
Sleep and Mood
- Sleep and mood are closely connected; poor or inadequate sleep can cause irritability and stress, while healthy sleep can enhance well-being.
- Chronic insomnia may increase the risk of developing a mood disorder, such as anxiety or depression.
- Poor sleep and feelings of depression or anxiety can be helped through a variety of treatments, starting with improved sleep habits, and, if needed, extending to behavioral interventions and an assessment for a sleep or mood disorder.
People who have problems with sleep are at increased risk for developing emotional disorders, depression, and anxiety – Dr . Lawrence J. Epstein
The Link Between Sleep and Mood
You probably know firsthand that sleep affects mood. After a sleepless night, you may be more irritable, short-tempered, and vulnerable to stress. Once you sleep well, your mood often returns to normal.
Studies have shown that even partial sleep deprivation has a significant effect on mood. University of Pennsylvania researchers 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 subjects resumed normal sleep, they reported a dramatic improvement in mood.
Not only does sleep affect mood, but mood and mental states can also affect sleep. Anxiety increases agitation and arousal, which make it hard to sleep. Stress also affects sleep by making the body aroused, awake, and alert. People who are under constant stress or who have abnormally exaggerated responses to stress tend to have sleep problems.
Insomnia and Psychological Problems
“There’s a big relationship between psychiatric and psychological problems and sleep. So people who are depressed or have anxiety often have trouble with sleep as part of those disorders,” says Dr. Lawrence Epstein, Medical Director of Sleep Health Centers and an instructor at Harvard Medical School.
Difficulty sleeping is sometimes the first symptom of depression. Studies have found that 15 to 20 percent of people diagnosed with insomnia will develop major depression.2 While sleep research is still exploring the relationship between depression and sleep, studies have shown that depressed people may have abnormal sleep patterns.
Sleep problems may, in turn, contribute to psychological problems. For example, chronic insomnia may increase an individual’s risk of developing a mood disorder, such as depression or anxiety.
In one major study of 10,000 adults, people with insomnia were five times more likely to develop depression. Lack of sleep can be an even greater risk factor for anxiety. In the same study, people with insomnia were 20 times more likely to develop panic disorder (a type of anxiety disorder).5 Another study showed that insomnia is a reliable predictor of depression and many other psychiatric disorders, including all types of anxiety disorders.
Addressing Sleep Problems Makes a Difference
If you sleep poorly and feel depressed, anxious, or less emotionally responsive, there are many treatments that can help. First, look at your sleep habits and see if there are steps that you can take on your own to improve the quantity and quality of your sleep. See Adopt Good Sleep Habits for tips on how to improve your sleep. If problems persist, you may wish to see a medical provider and ask about an evaluation for sleep problems and mental health concerns. After an evaluation and diagnosis, your provider can advise you on the best course of treatment. Options may include behavioral or other forms of therapy and/or medications. You can read about and watch a video of a behavioral sleep consultation in the Healthy Sleep module.
Even if you do not have underlying sleep problems, taking steps to ensure adequate sleep will lead to improved mood and well-being. Sheila, a Boston district attorney and mother, became sleep deprived due to the conflicting demands of a full-time job and caring for her young children. She began to feel cranky, irritable, and uncharacteristically depressed. When she got both of her children on a consistent sleep schedule, she herself started sleeping an average of seven to eight hours a night and her mood improved considerably.
Sleep and Memory
- Only 11 percent of American college students sleep well, and 40 percent of students feel well rested only two days per week.
- Inadequate sleep appears to affect the brain’s ability to consolidate both factual information and procedural memories about how to do various physical tasks.
- The most critical period of sleep for memory consolidation is in the hours immediately following a lesson.
During sleep, your brain is taking your memories, reactivating and looking at them again, and storing them in a more efficient and effective form – Dr. Robert Stickgold
One Student’s Story
Several mornings each week, Liz, a Harvard freshman from Toronto, Ontario, rises before 6:00 a.m. to join her teammates for rowing practice. On days like these she seldom sleeps more than seven hours per night, but it’s not for lack of trying. In contrast to the college student stereotype, Liz often forgoes opportunities to socialize in order to get her schoolwork done and still get to bed at a reasonable time. Even without knowing just how important sleep is to her ability to learn, she tries to make time for it.
Only a month and a half into her first semester at college, Liz already wishes she had more time for sleep. The problem is: “You never feel like you’ve done enough,” she says, referring to her school demands. “If you’re not working, you feel like you should be. There’s always more to do.” For Liz, the many demands on her time include her chosen sport, as well as activities like studying for optional, extra-credit exams that she and her peers have come to view as mandatory for anyone trying to excel.
A Snapshot of Sleep in College
Of course, Liz isn’t alone. College students represent one of the most sleep-deprived segments of our population. Course work, sports and other extracurricular activities, and newfound independence all conspire to rob students of sleep. A 2001 study found that only 11 percent of college students slept well consistently, while 73 percent experienced at least occasional sleep issues. A 2007 survey by the American College Health Association found that 40 percent of students felt well rested no more than two days per week.2 No longer considered a harmless aspect of college life, poor sleep is now thought to have a significant impact on memory and learning.
Basics of Learning
Learning involves three distinct brain processes: acquisition, consolidation, and recall.
- Acquisition is the process by which the brain receives information—be it a list of facts or the proper technique for shooting a free-throw—and stores this information within its neural circuits as a memory.
- Consolidation is a process that can extend over minutes, hours, or even days, during which connections in the brain are strengthened, extended, and in some cases even weakened, so that a memory ends up in a more stable and useful form.
- Recall is the last important step in learning, in which the brain accesses and utilizes stored information, often bringing memories back to mind.
The Sleep Connection
Inadequate sleep negatively affects all three learning processes. Acquisition and recall suffer in the most recognizable way. It is simply more difficult to concentrate when we are sleep deprived; this affects our ability to focus on and gather information presented to us, and our ability to remember even those things we know we have learned in the past. The less obvious—but possibly more profound—impact of sleep deprivation on learning is the effect that many sleep researchers think it has on memory consolidation.
Although no one knows exactly how sleep enables memory consolidation, a number of studies have shown that a reduction in total sleep time or specific sleep stages can dramatically inhibit a person’s ability to consolidate recently formed memories. Poor sleep appears to affect the brain’s ability to consolidate both factual information—such as what you had for breakfast or that Paris is the capital of France—and procedural memories about how to do various physical tasks—such as riding a bicycle or playing the piano. Research suggests that the most critical period of sleep for memory consolidation is the one immediately following a lesson. If this opportunity is lost—such as when a student pulls an “all-nighter”—it generally can’t be made up. Even if sleep is “recovered” on subsequent nights, the brain will be less able to retain and make use of information gathered on the day before the all-nighter.
Making Time for Sleep
These findings have shed new light on the importance of making time for sleep, not only for college students, but for anyone who wants to continue to learn. However, that doesn’t mean finding the time for sleep is always easy. For many people—even those who recognize the importance of sleep—balancing work, school, family, social activities, and personal time can be difficult, and sleep is often one of the first activities to get squeezed out.
Early in her first semester at Harvard, Liz feels like she is maintaining a healthy balance, but just barely. Striving to get the most out of her time in college, she admits that it’s sometimes hard to see sleep as an important part of her scholastic and athletic objectives. But that’s exactly what many researchers say sleep is. Rather than thinking of sleep as wasted time or even time off, they say, we should instead view sleep as the time when our brain is doing some of its most important work.
Judgment and Safety
- Drowsy driving causes 1 million crashes, 500,000 injuries, and 8,000 deaths each year in the U.S.
- Just one sleepless night can impair performance as much as a blood-alcohol level of 0.10 percent, beyond the legal limit to drive.
- Like alcohol, sleep deprivation also affects judgment, making it harder to assess how impaired you are when you’re tired.
If you’re depriving yourself of sleep and you’re a police officer, doctor, nurse, or pilot, then there’s a very good chance that in the line of duty you may be exposing other folks to risk as well – Dr. Christopher P. Landrigan
A Tragic Example
Nineteen-year-old Candy Lynn Baldwin was well acquainted with the 80-mile drive between Baltimore, Maryland, and her home in the Eastern Shore town of Millington. She had made the drive, which crosses the Chesapeake Bay, many times. On Saturday evening, August 9, 2008, following a busy Friday night and full day Saturday preparing for and attending her mother’s wedding, Baldwin and a cousin set out for Baltimore. They didn’t give their return trip much thought, even though they knew they would be returning late.
Just before 4:00 a.m. Baldwin steered her 1997 Chevrolet Camaro onto the Chesapeake Bay Bridge toward home. By that time, she had been awake for many hours straight. In addition, her internal biological clock, a part of the brain that helps control the timing of alertness and sleep, was likely sending out strong signals that her body needed to sleep.
At the same time, John Short was pulling onto the far end of the massive bridge, driving a semi-truck full of refrigerated chicken. On this particular night, maintenance had forced both directions of traffic onto the same eastbound span. As the two vehicles converged at highway speeds, Baldwin nodded off and veered across the centerline, far too quickly for Short to avoid. Short’s attempt to avoid a crash, and the subsequent collision, sent his truck hurtling into the opposite lane before smashing through a guardrail and plunging into the water below. He died of multiple injuries and drowning, according to autopsy reports. Baldwin’s cousin escaped relatively unscathed, receiving only minor injuries. Baldwin herself sustained two broken kneecaps and damage to her spleen and liver. She has no recollection of the crash.
A National Epidemic
Although this is an extreme and tragic example of the hazards of driving while sleep deprived, the circumstances that led up to Baldwin’s accident are all too common. According to a National Sleep Foundation survey, one-third of all adult drivers say they have fallen asleep at the wheel.1 On the basis of the best available research, the Institute of Medicine estimates that drowsy driving is responsible for 20 percent of all motor vehicle crashes. That means that drowsy driving causes 1 million crashes, 500,000 injuries, and 8,000 deaths each year in the U.S.2
Driving is not the only activity negatively impacted by insufficient sleep. Virtually any task or profession that requires alertness and sound judgment may be affected by too little sleep. The medical profession, for example, is notorious for the long, sleepless hours required of doctors, nurses, and other healthcare providers, and this has an impact on the quality of care patients receive. Although the precise number of medical errors attributable to insufficient sleep is unknown, a randomized, controlled trial at Harvard’s Brigham and Women’s Hospital found that more than one-quarter of the errors that interns (first-year doctors-in-training) made in the care of ICU patients were attributable to their traditional extreme work schedules. Given that medical errors are responsible for as many as 98,000 deaths each year in the U.S., the reduction of doctors’ and nurses’ sleep deprivation has become a major public health issue.
How Poor Sleep Affects Performance
Several sleep-related factors can affect an individual’s ability to stay alert and perform a task safely and competently. The first is the number of hours that person has been continuously awake. With each hour of wakefulness, the drive to sleep increases and alertness fades. Another common factor is insufficient sleep on a regular basis, also known as chronic sleep deprivation. Scientists have found that a small nightly decrease in sleep has serious cumulative effects; for instance, a week and a half spent sleeping just six hours per night, rather than seven to nine, can result in the same level of impairment on the tenth day as being awake for the previous 24 hours straight.6 Another factor is an individual’s internal biological clock. Shift workers, in particular, are affected by the timing of their internal clock, especially when they try to be alert when their internal clock says they should be sleeping, or when they try to sleep when their clock says they should be awake.
Drowsy or Drunk, the Effects Are Similar
Studies have shown that staying awake for just 17 to 19 hours straight impacts performance more than a blood-alcohol level of .05 percent (the level considered legally drunk in most western European countries). This level of impairment slows an individual’s reaction time by about 50 percent compared to someone who is well rested. Twenty-four hours of continuous wakefulness induces impairments in performance equivalent to those induced by a blood-alcohol level of 0.10 percent, beyond the legal limit for alcohol intoxication in the United States.
Perhaps even more profound is the effect of poor sleep on judgment. The prefrontal cortex, an area near the front of the brain responsible for logical reasoning and complex thought, seems particularly vulnerable to sleep deprivation. Experts think this may explain why people typically have such a hard time recognizing their own fatigue and level of impairment. Like the drunk driver who thinks he or she is just fine to drive, the tired driver is not always the best judge of his or her ability to operate a vehicle safely.