Research suggests there’s a connection between a healthy gut and healthy sleep, but it’s not yet clear whether interventions to improve one can help the other.
The gut microbiome is the community of trillions of bacteria that reside inside every person’s digestive tract. And during the past decade, research into the microbiome and its role in human health has been one of the hottest and most revelatory areas of medical science.
It seems like every week, a new study offers fresh insights about gut bacteria and their connection to the function of the human body. And that connection extends to sleep.
Your Brain and Your Gut Know Each Other Pretty Well
To understand why the gut has a relationship with your sleep, it’s first important to know that your gut actually has a very close (and well-established) relationship with your brain. Experts who study the microbiome say what’s in your gut affects your sleep thanks, at least in part, to what they call the “gut-brain axis.”
The brain is the body’s command center, so it’s constantly sending and receiving information from every one of the body’s parts and systems. But there’s evidence that the connection between the gut and the brain is especially strong and complex, says Emeran Mayer, MD, a professor of medicine, physiology, and psychiatry at the University of California in Los Angeles and the author of The Mind-Gut Connection.
Dr. Mayer says that the gut’s microorganisms seem to possess several signaling mechanisms that allow them to communicate with the brain in ways that can influence a person’s mood, appetite, stress level, and much else. “One of our hypotheses is that these bacteria produce metabolites that go back to the brain,” he says. (Metabolites are small molecules that result from the breakdown of food.) Another possibility, he says, is that gut bacteria trigger the release of immune system chemicals, which the brain detects and reacts to.
While researchers are still sorting out the nitty-gritty details concerning how the brain and gut interact, Mayer says what has been established so far is that the brain does respond to changes in the microbiome. And accordingly, changes in the microbiome seem to be related to sleep.
Wait, Sleep Affects What’s Going On in the Gut?
There’s evidence that the composition of the microbiome fluctuates during the day and night, and that these fluctuations play a role in programming some of the body’s sleep genes, according to a report published in December 2016 in the journal Cell. Some of these sleep genes regulate the body’s circadian cycles, which are sort of like internal clocks that tell the body when it’s time to feel tired or alert, that study found.
“The body’s biological clock works in synergy with the microbial clock,” write the authors of a study published in 2018 in Frontiers in Psychiatry on the microbiome and insomnia. Messing with a person’s sleep seems to change their microbiome, and changes to the microbiome may help or hurt sleep, their research suggests.
More research, including a study presented at Sleep 2019 (the annual meeting of the Associated Professional Sleep Societies, which includes both the American Academy of Sleep Medicine and the Sleep Research Society), has shown that more diversity in the gut in terms of the types of bacteria present is associated with improved sleep quality and lower rates of sleepiness. (More diversity of the bacteria in the gut has also been found to be protective against other health problems, like obesity, gastrointestinal disease, certain cancers, and neurological disorders, too.) And a study published in January 2017 in Frontiers in Behavioral Neuroscience found that stressed-out rats that were fed prebiotics, the nondigestible fibers that foster the growth of healthy bacteria, slept more soundly at night than rats fed a normal diet. (The researchers shocked the rats’ tails during the day to induce a state of stress.)
Together, the research findings suggest that sleep and the gut microbiome are indeed related and that a healthy gut seems to promote healthy sleep. But experts say that bolstering microbiome health is easier said than done — and whether improving your gut can fix sleep problems is a question without a simple answer.
Could Prebiotics, Probiotics, or Dietary Interventions Help Fix Sleep Problems?
In a word: maybe. But some of the latest science suggests that changing your microbiome in healthy ways isn’t as simple as popping a probiotic supplement.
One example: During the past decade, several promising studies have found evidence that probiotic supplementation could help a person’s microbiome bounce back after a course of antibiotics, which tend to kill good bacteria and bad bacteria indiscriminately. But a study published in September 2018 in the journal Cell found just the opposite. In that study, a specially prepared cocktail of probiotic bacteria actually interfered with the healthy recolonization of people’s microbiomes after they’d been on antibiotic drugs. These sorts of conflicting results demonstrate that improving the health of the microbiome is a complicated and unpredictable business (and may explain why there’s not yet consensus from experts on such interventions in clinical practice).
Mayer says that, in rodent models, probiotics have consistently produced benefits — many of which have received substantial media coverage. And these findings have allowed companies that make probiotics to label their products as “research-backed” or “evidence-based.” But he says the benefits of giving probiotics to real people have been far less consistent and, in some rare cases, have led to unwanted side effects. He says that the September 2018 Cell study is evidence of this concern.
While it’s possible that taking a pro- or prebiotic supplement could help improve the health of a person’s gut microbiome — and by extension, their sleep — Mayer says that outcome is far from certain. He also points out that there’s immense person-to-person variation in the makeup of the gut microbiome for all of us, so what works for one person may not work for another. “We’re dealing with a very complex ecosystem that we don’t fully understand,” he says.
Another study presented at the Sleep 2019 meeting found that among individuals sleeping for shorter periods and at different times than they were used to, more diversity in gut bacteria (as observed by measuring the fecal metabolome, or the small molecules produced by the bacteria that make up the gut microbiome) was associated with an increased ability to stay awake and alert following the periods of poor sleep. The study included only 15 adults, so it’s too small to draw sweeping conclusions, but the researchers note that it suggests a healthy gut microbiome might be of extra importance to people in safety-critical professions whose jobs limit their ability to get adequate, regular sleep (like healthcare workers and members of the military).
The makeup of a person’s fecal bacteria changes when that person is deprived of sleep or asked to adhere to unusual sleep-wake schedules. Those bacteria changes were also associated with problems staying awake and alert, the study found.
It’s early days in the medical community’s exploration of the microbiome-sleep relationship. Eventually, your doctor may be able to suggest a specially designed probiotic that can help you sleep better, but we’re not quite there yet.
In the meantime, Mayer suggests doing the things that we know promote a healthy gut, like exercising and managing stress. Eat natural probiotic foods — like kefir, kimchee, and sauerkraut — two or three times a week. “Each of these has a different combination of microbes, so if you rotate them, you probably have the best chance to get a benefit,” he says. Also, people have been eating these foods for centuries, so their safety is not in question, he adds.
Markham Heid
JUN