Not getting enough sleep can take real time off your life. The link between sleep deprivation and mortality has been shown in a wide body of rigorous scientific research. Sleep is essential for survival. Studies in animals have demonstrated that going without any sleep will eventually be, over a period of days or weeks, lethal.
And studies in people have established the association between short sleeping and an increased risk of death. For example, a review of research published in the journal Sleep found an average of a 12% higher risk of dying among short sleepers. Short sleepers were people sleeping less than 7 hours a night—in many studies sleeping less than 5.
(We’re talking about sleep deprivation today. But I can’t move on from mentioning this research review above without noting that it also found sleeping too much associated with higher risk of dying—a whopping 30% increase. I’ll come back to this topic of excessive sleeping again. It’s an important one. In the meantime, here’s an article I wrote about the risks of oversleeping.)
And a 12% average increase to risk means, of course, that some individual studies found the risk of early death associated with short sleep to be even higher—like this study, which analyzed the connection over a 22-year period in more than 21,000 twins, and found increases in mortality of 26% for men, and 21% for women.
The big question is: Why? Scientists have a well-established association between lack of sleep and risks of early death. But what is the cause underlying this association? That’s a powerfully important question with huge implications for treating sleep disorders and other health problems.
There’s not likely to be a simple answer, or a single route or mechanism that connects short sleep to mortality risk. That’s because sleep is connected to so much else that the body does—from metabolism to brain function to immunity. Poor sleep is a factor in the chronic, age-related diseases of our time, including diabetes, cardiovascular disease, cancer and neurodegenerative disorders such as Alzheimer’s.
New research out of Harvard Medical School contains some potentially game-changing information about one particular pathway by which sleep deprivation causes death. It’s a path you’ve heard me talk about before in relation to sleep.
I’ve written a number of times about the sleep-gut connection and its widespread influence over health issues such as weight and metabolism, immunity, and stress. Recently, I talked about how prebiotic foods can help improve gut health,resulting in reduced stress and more time spent in deep and restorative stages of slow-wave and REM sleep.
You’re probably familiar at this point with how the health of your gut contributes to your overall health and well-being. Your intestines are home to the largest concentration of micro-organisms that make up what scientists call the “microbiome.”
How the gut microbiome relates to sleep
The human microbiome is made up of trillions of tiny microbes. Many are bacteria, but there are also viruses, fungi, and protozoa. These microbial organisms live all throughout the body, but the single largest microbial ecosystem is in the intestines.
The collection of organisms within the microbiome—both the types and amounts of different bacteria and other microbes—has broad effects on mental and physical health, influencing mood, metabolism, cardiovascular and circulatory health, as well as the immune system, and our risk for chronic disease.
The gut microbiome is frequently called our “second brain.” That’s because the gut is home to a nervous system and about 100 million neurons. The nervous system of the microbiome is in constant communication with the brain and our central nervous system, helping to regulate hormone production, immune system function, appetite, digestion and metabolism, mood and stress responses.
On the sleep front, the microbiome produces some of the body’s melatonin (which is also produced in the brain) as well as other hormones and neurotransmitters involved with sleep, including dopamine, serotonin, and GABA .
Our microbiome is regulated by circadian rhythms. Research has shown that when circadian rhythms are disrupted, the health and functioning of the microbiome suffers. At the same time, so is sleep. The health of the microbiome can also be disrupted by poor diet, stress, illness, and excessive use of some medications including antibiotics.
We know from recent research that:
Irregular sleep schedules can disrupt a healthy gut. This recent study in the journal Nature has reveals the connections between sleep, circadian bio rhythms, and the gut microbiome. It points to a regular sleep routine as one way to protect and promote optimal gut and immune system functioning. Sticking to a sleep routine, limiting nighttime light exposure, managing stress, and practicing healthy, sleep-friendly eating habits are all ways to keep your circadian clock—and your gut microbiome—functioning optimally.
A couple nights of poor sleep can harm your microbiome. The relationship between sleep and the microbiome is a two-way street. Our microbiota affects how we sleep. In turn, sleep and circadian rhythms affects the health and diversity of the influential microbial ecosystem that lives in our gut. Recent research shows not sleeping enough can quickly have a negative effect on microbiome health. After only two nights of partial sleep deprivation, European scientists who conducted this 2016 study found:
- A signifiant drop in beneficial bacteria
- Changes to the composition of micro-organisms in the microbiome that are linked specifically to obesity and type 2 diabetes
- A significant reduction in insulin sensitivity
Restless, poor quality sleep affects the microbiome AND metabolic health. People who experience sleep disorders, particularly obstructive sleep apnea, often contend with this type of poor sleep quality, which keeps them from spending sufficient time in the most restorative stages of deep sleep and REM sleep.
We know fragmented sleep leads to changes in metabolism and eating patterns that increase risks for obesity and other metabolic disorders, including type 2 diabetes. In the past several years, we’ve also seen a growing body of evidence that dysfunction in the microbiome is a significant factor driving the metabolic changes that lead to obesity and other metabolic disorders. Recent research suggests that fragmented sleep may play an important role in the microbiome-driven effects on metabolic health, in part by triggering inflammation that leads to metabolic dysfunction.
What does the gut have to do with sleep deprivation and early death?
Clearly there’s a lot going on in the sleep-gut relationship. We’ve learned a lot already. This latest breakthrough is especially significant and interesting, because it suggests a cause-and-effect chain of activity between sleep deprivation and premature death.
The scientists studied the link between lack of sleep and early death in a population of fruit flies. Scientists deprived the flies of sleep, and during their prolonged wakefulness the scientists examined the flies for signs of physiological damage from their lack of rest.
Here’s a snapshot of what they learned:
- Over a period of 10-20 days without sleep, all the flies eventually died. No big surprise here—as studies in animals have shown, sleep is essential for survival and prolonged lack of sleep leads to illness and death.
- When sleep deprived, the fruit flies produced a lot of a particular type of molecule in their guts, known as reactive oxygen species, or ROS. ROS molecules are volatile and unstable, and sometimes known by another name you might know: free radicals. ROS molecules, aka free radicals, damage healthy cells and DNA, through a process that’s known as oxidative stress—essentially, when enough free radicals are produced that the body can’t limit the cellular damage they do. Research suggests that sleep is a time when the body works to suppress oxidative stress and neutralize the damage of free radicals. This study was showing the opposite to be also true: without sleep, damaging ROS molecules became abundant.
- Production of these ROS molecules in the gut always took place before the fruit flies died. To confirm that sleep deprivation led to increased production of ROS molecules in other animals, scientists tested mice. They, too, experienced a boost in ROS molecules in the gut when without sleep.
- Scientists treated the flies with antioxidants, to neutralize the ROS molecules. This changed the course for the flies. With their ROS molecules eliminated, the fruit flies didn’t die, despite being sleep deprived. Moreover, scientists discovered the flies were able to maintain normal activity and normal lifespans, without sleeping.
The takeaway? Our guts may be a place where sleep deprivation inflicts direct biological damage that puts us at greater risk for illness and death. We need to see more research, but this is a really fascinating and important development.
Another takeaway? This new insight may offer new avenues to treating the negative effects of poor quality and insufficient sleep. Targeting oxidative stress in the gut might be a method for neutralizing and minimizing the damage that comes from not getting enough sleep.
What to do with this information
Take care of both your sleep and your gut! The good news is, both respond to many of the same habits and practices.
Control your stress. Not easy these days, I know. But really important, for both sleep and gut health. Here’s a recent primer I wrote on how sleep and stress intersect.
Exercise and eat well. You knew I’d be going here, right? Along with sleep, physical activity and diet are the foundations of long-term health and vitality. Both sleep routines and the health of the microbiome benefit from regular exercise and a diet that’s unprocessed, built on whole foods, and avoids sugars. Here’s my rundown on how to get more prebiotics into your diet for a healthier gut, better sleep, and less stress.
Stick to your sleep routines. Both sleep and the activity within the gut microbiome are regulated by circadian clocks (the gut microbiome is full of peripheral clocks that communicate with the master circadian clock in the brain). Our circadian rhythms create biological routines for our bodies—and these rhythms become stronger when we lean into those routines. Sleep on a consistent schedule. And use your chronotype to determine the best schedules for sleeping, eating, exercise—and everything else!
Michael J. Breus, PhD, DABSM
The Sleep Doctor™