Why We Sleep: The New Science of Sleep and Dreams

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  • Sleep scientist and author Matthew Walker suggests a lack of sleep throughout industrialized nations is having a catastrophic impact on our health and wellness, and is fast becoming one of our greatest public health challenges
  • More than 20 large-scale epidemiological studies, tracking millions of people over many decades, report the same clear relationship: the shorter your sleep, the shorter your life
  • Rather than being an optional lifestyle choice, Walker asserts sleep is a non-negotiable, biological necessity that provides a foundation for every aspect of your mental and physical health
  • Sleeplessness has been shown to have a devastating effect on your health and well-being, contributing to chronic illnesses such as dementia, including Alzheimer’s disease, cancer, diabetes, heart disease and obesity
  • Walker suggests more vehicle crashes in the U.S. are caused by sleep-deprived drivers than those involving alcohol and drugs combined; when you drive drowsy, you put your life and the lives of countless others in jeopardy

By Dr. Mercola

In the featured video, professor Matthew Walker, Ph.D., founder and director of the University of California Berkeley’s Center for Human Sleep Science and author of the book "Why We Sleep: The New Science of Sleep and Dreams," shares the latest discoveries about sleep and how it impacts virtually every area of your physical and mental health.

I read Walker’s book last fall, and share his view that sleep is profoundly important — even more important than diet and exercise. I say this because diet and exercise will have minimal effects on your body if you are constantly exhausted and it is unlikely you will have the energy to eat well or exercise if you are always tired. Beyond that, sleeplessness has been shown to contribute to chronic illnesses such as dementia, including Alzheimer’s disease, cancer, diabetes, heart disease and obesity.

In his book, Walker suggests insomnia is “one of the most pressing and prevalent medical issues facing modern society,” yet it is rarely acted on in ways reflecting its importance. He notes the “sleep aid” industry, encompassing prescription sleeping pills and over-the-counter sleep medications, is a $30 billion-a-year industry in the U.S.

Sadly, desperate people are putting money toward drugs that have not only been shown to be ineffective for solving sleep problems, but also are known to increase your risk of cancer, heart disease and stroke. Most adults need at least eight hours of high-quality sleep a night, and children and teenagers even more. The reality is about 1 in 3 Americans gets less than seven hours of sleep a night and more than 83 million adults in the U.S. are sleep-deprived.1,2

While losing an hour or two of sleep may not seem like a big deal, Walker presents data suggesting even a single night of poor sleep can have devastating consequences. If you have not yet prioritized proper sleep as one of the non-negotiables in your life, Walker’s research may be the impetus to move you in that direction.

Sleep-Deprived Drivers More Dangerous Than Those Under the Influence

With respect to sleep deprivation and auto accidents, Walker speaks passionately about this subject in his book. He says one person dies every hour in the U.S. due to a fatigue-related error, and vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined. If you drink alcohol or take medications that make you sleepy and then drive, you are exponentially increasing your risk of suffering a crash, injury or death due to drowsy driving. States Walker:

“This coming week, more than 2 million people in the U.S. will fall asleep while driving their motor vehicle. That’s more than 250,000 every day, with more such events during the week than on weekends, for obvious reasons. More than 56 million Americans admit to struggling to stay awake at the wheel of a car each month. As a result, 1.2 million accidents are caused by sleepiness each year in the U.S.”

Drivers of cars are not alone in threatening the safety of our roadways. Walker suggests drowsy truckers may be even more dangerous, mainly because approximately 80 percent of truck drivers in the U.S. are overweight and 50 percent are clinically obese, putting them at risk of sleep apnea. He says:

“[These health conditions] place truck drivers at a far, far higher risk of a disorder called sleep apnea, commonly associated with heavy snoring, which causes chronic, severe sleep deprivation. As a result, these truck drivers are 200 to 500 percent more likely to be involved in a traffic accident. And when a truck driver loses his or her life in a drowsy-driving crash, they will, on average, take 4.5 other lives with them.”

When you drive on less than five hours of sleep, you are 4.3 times more likely to be involved in a crash than a well-rested driver; on just four hours of sleep, your risk of crashing is 11.5 times higher.3 Beyond car crashes, studies suggest poor sleep is related to many other health conditions that can also shorten your life. In his book, Walker states:

“[T]here are more than 20 large-scale epidemiological studies that have tracked millions of people over many decades, all of which report the same clear relationship: the shorter your sleep, the shorter your life. The leading causes of disease and death in developed nations — those that are crippling health care systems, such as heart disease, obesity, dementia, diabetes and cancer — all have recognized causal links to a lack of sleep.”

Lack of Sleep Does Damage to Your Brain

While it’s common to experience a certain amount of “brain fog” after a poor night’s sleep, the damage to your brain from chronic lack of sleep is not something you can address simply by drinking more coffee or taking a nap midday. Walker cites the following brain-related effects from lack of sleep:

  • Due to your hippocampus shutting down, you will experience a 40 percent deficit in your brain with respect to its ability to make new memories
  • Your emotional and mental health becomes destabilized because the emotional circuits in your brain become hyperactive and irrational due to lack of sleep
  • Your amygdala, one of your brain’s centerpiece regions for generating strong emotional reactions, including negative ones, becomes about 60 percent more reactive than usual, resulting in increased emotional intensity and volatility

Walker presents an aspect even more concerning to your brain with respect to poor sleep and that is the belief it may be a contributing factor to numerous psychiatric conditions. He states: “We are now finding significant links between sleep disruption and depression, anxiety (including post-traumatic stress disorder), schizophrenia and, tragically, suicide as well. In fact, we cannot find a single psychiatric condition in which [the subject’s] sleep is normal.”

Furthermore, Walker emphasizes that too little sleep during your adult life span significantly raises your risk of developing Alzheimer’s disease. This is so because amyloid-beta deposits that would normally be cleaned out of your brain nightly during deep sleep instead accumulate as plaques and kill off surrounding cells.

This waste removal system has been dubbed the glymphatic system and it gets into your brain by piggybacking on blood vessels. By pumping cerebral spinal fluid through your brain's tissues, your glymphatic system flushes waste from your brain back into your circulatory system and onto your liver for elimination. 

Because your glymphatic system ramps up its activity during sleep, when you don’t get enough sleep, the damaging plaques build up, attack and degrade certain regions of your brain. Walker notes a brain affected by Alzheimer’s has lost most of its ability to remove the amyloid-beta waste products, mainly because it is caught in a vicious cycle: more amyloid, less deep sleep; less deep sleep, more amyloid.

Sleep Loss and Heart Attacks Go Hand in Hand

Regarding the effects of losing sleep on your heart, Walker suggests even one hour makes a big difference. He says:

“There is a ‘global experiment’ that is performed on 1.6 billion people across 70 countries twice a year, and it’s called daylight saving time. In the spring when we lose one hour of sleep, we see a subsequent 24 percent increase in heart attacks. In the fall, when we gain one hour of sleep, we see a 21 percent decrease in heart attacks. That is how fragile your body is with even the smallest perturbations of sleep, but most of us don’t think anything about losing an hour of sleep.”

Walker, in the book, notes a similar relationship to sleep and heart attacks called out in a Japanese study of more than 4,000 male workers whose sleep habits were evaluated during a 14-year period. Workers sleeping six hours or less were 400 to 500 percent more likely to suffer one or more cardiac arrests than those sleeping more than six hours.

This was true even after adjusting for other known cardiac-risk factors such as smoking, exercise and body weight. Said Walker, “A lack of sleep more than accomplishes its own, independent, attack on the heart.”

In his book, Walker notes that sleep deprivation also shuts down growth hormone, which is considered to be a great healer of your body, normally surging at night. Walker suggests without growth hormone to replenish the lining of your blood vessels (endothelium), they will be gradually shorn and stripped of their integrity. “The hypertensive strain sleep deprivation places on your vasculature means that your body can no longer repair those fracturing vessels effectively,” notes Walker.

Over time, the damaged and weakened state of your arteries becomes systemically prone to atherosclerosis (hardening of the arteries), causing vessels to rupture and putting you at risk of heart attack and stroke. Walker also underscores the effects of sleep on your cholesterol: “[S]tudies have found that short sleep duration will also disrupt the activity of genes regulating cholesterol.

In particular, a lack of sleep will cause a drop in high-density lipoproteins (HDLs) — a directional profile that has consistently been linked to cardiovascular disease.”

Other Serious Diseases Are Linked to Lack of Sleep

With respect to sleep loss and cancer, Walker asserts that after just one night of only four hours of sleep, your natural killer cells — the ones that attack the cancer cells that appear in your body every day — drop by 75 percent. Given the hit your immune system takes due to the loss of these disease-fighting cells, it comes as no surprise researchers have made significant links between short sleep and numerous forms of cancer, including cancers of the bowel, prostate and breast.

Walker notes the link between lack of sleep and cancer is so strong that the World Health Organization, since 2007, has tagged shift work as a “probable human carcinogen” because it causes circadian disruption.4 “Their concern is jobs that may induce cancer because of disruptions to your sleep-wake cycle,” said Walker. If you routinely forgo proper sleep, he says data shows “you will live a shorter life, and the quality of that shorter life will be significantly worse.”

That said, if you work erratic hours, particularly the night shift, you most assuredly are putting yourself at greater risk for diseases such as cancer, diabetes and obesity. While lack of sleep increases your risk of developing cancer, it also influences your ability to heal from it successfully. Says Walker, “[I]f you are fighting a battle against cancer and not getting sufficient sleep, that cancer may grow more quickly and aggressively.”

In 2014, research5,6 conducted at the University of Chicago, led by Dr. David Gozal, a professor of pediatrics and sleep physician, linked disrupted sleep to tumor growth in lab mice inoculated with cancer cells. Compared to the mice who received normal sleep, the tumor growth in the sleep-disrupted mice was significantly larger in size and faster spreading.

Citing Gozal’s work, Walker calls sleep loss an “accelerant” for cancer. “We now know it produces a more harmful biological fertilizer for the rapid and rampant growth of cancer,” he stated.

Lack of Sleep Also Associated With Addictions, Depression and More

In his book, Walker calls out sleep disturbance as a recognized hallmark associated with the use of addictive substances. Addicts of various kinds are generally not good sleepers and those same addictions are well-known for interfering with quality sleep. States Walker: “Insufficient sleep also determines relapse rates in numerous addiction disorders, associated with reward cravings that are unmetered, lacking control from … the brain’s prefrontal cortex.”

Walker notes children who were chronic poor sleepers in childhood are at a greater risk of drug and alcohol use in the later adolescent years, even when controlling for such high-risk traits as anxiety, attention deficits or parental history of drug use. Insufficient sleep has also been linked to aggression, bullying and other behavior problems in children across a variety of ages. While the precise causes of depression are not always evident, certain factors such as poor sleep have been shown to contribute to it.7

Insomnia, for example, has been shown to influence the onset, severity and recurrence of depressive episodes. If you routinely suffer from insomnia, you are at twice the risk of developing depression as compared to individuals who sleep well. A study published in the Journal of Neuroscience8,9 suggests your brain’s reward center may help protect you from the depressive symptoms traditionally associated with poor sleep.

Researchers at Duke University have taken a closer look at the involvement of your ventral striatum (VS) — an area of your brain responsible for reward processing and motivation. Their objective was to better understand the role your VS may play with respect to depression and poor sleep. Dysfunction in your VS is thought to be associated not only with depression, but also with addiction, bipolar disorder, obsessive-compulsive disorder and Parkinson’s disease.

After testing 1,000 university students to explore the relationship among depression, self-reported sleep patterns and VS activity, researchers concluded participants with higher reward-related VS activity were less likely to report symptoms of depression even when their sleep quality was poor. Further research in this area may help scientists gain further insight into how depression works, as well as assist them in identifying biomarkers for depression risk.

Prioritize Sleep and Take Steps to Ensure You Get Quality Sleep

Regardless of your thoughts on the topic, research linking sleep deprivation to chronic disease and shorter life spans cannot be ignored. The scientific facts underscore my belief that there is no substitute for getting a full night’s rest. Nor is there any excuse for ignoring your body’s need for sleep. While diet and exercise are vital to your health, without proper sleep, your efforts in those areas will be less effective. Says Walker:

“Sleep is not an optional lifestyle luxury. Sleep is a nonnegotiable, biological necessity. It’s a life-support system. The decimation of sleep throughout industrialized nations is having a catastrophic impact on our health [and] our wellness … It’s a silent sleep epidemic, and it is fast becoming one of the greatest public health challenges we now face.”

Given its importance, I encourage you to take a few moments today to evaluate your sleep habits. Are you getting enough sleep? If not, what’s one change you can make to improve your sleep? If you need help getting started, check out my "33 Secrets to a Good Night’s Sleep".

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