You can sleep when you’re dead. So goes an old adage that should be scratched from your vocabulary.
Sleep accounts for a quarter to a third of your life, and for good reason. Much about sleep remains mysterious, though current theory suggests that among the benefits is the fact that the body uses sleep to flush toxins from your brain. This is, in its own way, a broader immune system function of cleaning the Festival of Life of detritus. There are myriad other health benefits of sleep. Improved memory, cognition, and mood; less inflammation, and you know now how huge that is. Or, if you prefer to look at the other side of the coin, people who get insufficient sleep can put their health at tremendous risk.
Sleep problems predict death.
People who experience prolonged sleep disturbance are more likely to die, and to die earlier, than people who don’t. “The effect sizes are comparable to other known risk factors, like being sedentary, being overweight, having depression,” said Dr. Irwin.
Studies in lab animals have shown even clearer links between sleep and health. Sleep-deprived rats die.
In humans, sleep problems are rampant, as recounted in a recent paper by Dr. Irwin. Roughly 25 percent of Americans have sleep problems, and “insomnia is one of the most ubiquitous complaints in psychiatric populations,” the research shows, at least telling you that you’re not alone.
The risk of early death from sleeplessness was shown with considerable confidence in a 2010 research roundup of sixteen studies involving 1.3 million subjects. Among those studies was one that found the optimal sleep level for longevity was seven hours, with a particularly heightened risk of death for those who slept fewer than 4.5 hours. (This behavior is rampant. A poll published in 2008 found that 44 percent of adults were getting less sleep than they said they needed, around seven hours, while 16 percent got fewer than six hours.)
Curiously, the same 2010 study also found an increased risk for people who reported sleeping more than 8.5 hours. I asked Dr. Irwin about that figure, and he said it still wasn’t well understood. “It’s really been debated a long time.”
The theory has been that when people slept longer, it was indicative of an underlying medical condition that eventually led to premature death. But Dr. Irwin said a close look at the studies doesn’t bear that out. While Dr. Irwin is doing ongoing research to get at the answer, he does have a hypothesis. He thinks that people who report sleeping longer are actually people who are spending more time in bed but not truly sleeping longer. He thinks they fundamentally have a “sleep maintenance” problem that is more akin to getting insufficient sleep, and so they spend many hours in bed to overcompensate.
The bigger issue is sleeplessness.
The work of Dr. Irwin and others has shown that when it comes to the dangers of sleeplessness, all roads lead through the immune system. “The effect of sleep on the immune system is the critical link that’s driving that risk.”
I mentioned the sympathetic response, the flight-or-fight response, above. It has a powerful impact on heart rate, blood pressure, the flow of digestive juices, and other core involuntary functions. When we sleep, the system slows markedly and the norepinephrine and epinephrine turn off. “When we don’t sleep, that activation continues at daytime levels,” Dr. Irwin said.
His research has also shown that people who are deprived of sleep experience a decrease in activity of natural killer cells “to the same level of people who are depressed or stressed.” So sleep sets off and intensifies an adrenaline-fueled dampening of the immune system.
Other research shows that sleep loss leads to specific changes to at least ten interleukins, along with other inflammatory processes, and studies show that response to vaccines is diminished in people with sleep deprivation, suggesting our immune systems don’t learn as well when we are tired. People who don’t sleep are more likely to develop heart disease, cancer, and depression. “We now have compelling evidence that, in addition to cognitive impairment, sleep loss is associated with a wide range of detrimental consequences, with tremendous public-health ramifications,” one recent paper found. I like the direct language used in a different scientific paper that looked at what happens to rats when they are sleep deprived. “There was failure to eradicate invading bacteria and toxins.”
It might come as little surprise that a healthy immune system helps promote or mediate sleep, with various studies showing that several key cytokines—those immune-system signals—can promote sleep. This happens when you’re healthy but also when you are sick, or getting sick; then, your immune system sends stronger signals creating a feeling of fatigue, telling your body to rest, and creating more resources to fight infection. All of this means the relationship between sleep and the immune system is a tight and circular one.
Also, simply, lack of sleep often is caused by stress and leads to more stress.
So you get stressed, don’t sleep, your sympathetic response kicks in, your immune system gets dampened, and the cycle, through more stress and less sleep, spirals. Alone this is key. But Dr. Irwin offers a fascinating nuance.
He believes that only part of the immune system gets dampened by this cycle. Stress and lack of sleep, Dr. Irwin believes, make it tougher to fight viruses but easier, or at least less difficult, to fight bacteria.
His theory makes perfect sense from historical and evolutionary standpoints. Picture your forebear facing an acute threat—say, an attack from a lion or bear or from a fellow human with a spear, or simply having injuries from a fall or scratches from a rock or bush. The immediate threat would come from a puncture wound or bite and the bacteria that might be transferred by that injury. So it stands to reason that the immune system would favor lending its limited resources to a bacterial response over a viral one.
To be clear, the release of cortisol can dampen both types of immune responses—to allow us to remain alert during an acute threat—but Dr. Irwin sees the dampening as having a greater impact on a response to viruses.
In either case, virus or bacteria, these primitive responses can wind up having a perverse effect in the modern world. After all, these primitive systems kick in all the time, as if the body were responding to an attack by a lion or bear, but the actual threats are much different today, and often much less dangerous.
“Those same systems of alarm and threat can become activated in a social situation. You get into an interpersonal situation, an argument with your boss at work,” said Dr. Irwin. “The sympathetic nervous system gets hijacked. It’s just as if we were exposed to an acute threat in Neanderthal times and were hurt.”
Often, Dr. Irwin said, the culture adds another layer, pushing us forward, rather than letting the system settle down through withdrawal or sleep. “It’s a badge of honor to see how little sleep you can get by on. If you can sleep less and maintain function at work, you’re a better professional. You’re a better human being. That crazy logic has led to a sleep-deprived society, and that is having huge health consequences.”
As concerns autoimmunity, there hasn’t been a large study that has expressly tested the relationship among stress, sleep, and a hyperactive immune system, but Dr. Irwin says “there’s a good case to be made” for a link between sleeplessness and autoimmunity. At the very least, the indirect connection speaks for itself: Lack of sleep leads to stress and vice versa, creating a vicious cycle that disregulates the immune system.
Dr. Lemon, the Denver physician who treated Merredith and believes strongly in the hygiene hypothesis, says she tells patients worried about their immune systems, “Your job isn’t to keep your house spotlessly clean. You should sleep until you’re not tired anymore. Sleep is the easiest medicine to regulate. A single night alters your immune system. It blows things out of whack in one night.”
She says that she is by no means blaming people who get diseases like autoimmunity or cancer for their stress or sleeplessness.
Sometimes disease just happens.
It happened to Jason. He’s our last story, the most telling of all about this extraordinary moment in time when we’re putting to work nearly a century of understanding the balance of our immune system.