Bad sleep? Here’s the hidden gut issue experts warn you’re ignoring

The Night Owl Hiding in Your Gut

Ever wondered if that restlessness at bedtime could actually stem from your belly? To be more precise, from your microbiome—the bustling community of billions of microbes (bacteria, viruses, parasites) calling your intestines home. Sounds a bit far-fetched? Actually, the link between your gut’s health and the quality of your sleep is tighter than you might think.

This isn’t just a nighttime tale: Science is currently abuzz with research into how certain gut bacteria may act as sleep aids. Some even produce substances—homemade sleeping pills, if you will—released straight into the intestines and then whisked up to the brain via the gut-brain axis.

Bacteria, Broccoli, and Sleep: The Biochemical Ballet

The most notable of these substances is serotonin, crafted from tryptophan, an amino acid found in green veggies like broccoli. Back in November 2020, Professor Masashi Yanagisawa from the University of Tsukuba in Japan set out to investigate this phenomenon in rodents. He split them into two groups: some got antibiotics (which wipe out gut flora) for four weeks, while the others kept to their normal diet.

Here’s what happened: The sleep patterns of the antibiotic group were in shambles! They spent less time in deep, restorative sleep during their usual rest period and caught up on missed sleep when they should’ve been active. Translation: on a bad night, these mice were dozing off during their mousey “day.” The antibiotics wrecked their microbiome, shutting down serotonin production—which is the precursor to melatonin, the well-known sleep hormone.

But serotonin isn’t the only gut-produced molecule to watch. Meet butyrate, a fatty acid created by gut bacteria from dairy products and fibers found in veggies like asparagus, oats, artichokes, raw garlic, leeks, and onions. Once butyrate’s in your intestines, it heads straight for the liver via the portal vein (a major blood vessel) and gets stored there.

In May 2019, researchers at the University of Washington found that feeding rats hefty amounts of butyrate resulted in nearly 50% longer deep sleep, along with lower body temperatures and fewer episodes of REM sleep (that’s when the dreams get wild). They suspect butyrate acts as a « bacterial signal, » nudging us to drift off when it locks on to certain receptors in the liver’s wall or the portal vein. Like our own mini Sandman, ready to whisk us away to dreamland.

When Bad Sleep Disrupts the Gut Right Back

But it’s not a one-way street! Poor or broken sleep, chronic insomnia, or even just a rough night can actually shake up your gut flora. Case in point: Researchers at the University of Missouri studied mice experiencing regular hypoxia (think: less oxygen delivered by blood to key organs—similar to what happens in sleep apnea in humans). They discovered the mice’s bacterial balance was so disturbed that it might help explain why sleep apnea often goes hand in hand with cardiovascular problems.

Even more surprising—if you transplant this disturbed microbiome into healthy mice via fecal transfer (yes, that’s a real thing in experiments), the second set of mice develop similar sleep problems! How does this strange partnership between gut and sleep even work? The answer may lie in chronobiology, the study of our biological rhythms.

According to scientists, our gut bacteria have daily routines, just like us, following a circadian rhythm of roughly 24 hours. Our microbiome is dominated by two main bacterial families—Firmicutes and Bacteroidetes—which make up about 90% of the ecosystem.

• Firmicutes are early risers: they thrive during daylight hours and fade into the background by night.
• Bacteroidetes, on the other hand, are creatures of the night, feasting on the dietary fibers we consumed that finally reach the colon once we’re sound asleep.

But sometimes our rhythm and the bacteria’s rhythm get out of sync, for example after jet lag. A team from the Weizmann Institute of Science in Israel analyzed two volunteers’ gut microbes before and after they flew from the US to Israel.

Result: jet lag shuffled their microbiome composition, bumping up the proportion of Firmicutes. Having too many of these guys often hints at metabolic disruption (they’re found in higher amounts in people with obesity, by the way). This mismatch was temporary—after two weeks, the travelers’ microbes returned to normal. But if your daily rhythm stays out of whack, a sustained imbalance between Firmicutes and Bacteroidetes can upset your entire metabolism—disrupting the delicate ballet between you and your gut bugs.

How Immune Reactions and Sleepless Nights Tangle

Exactly how this mismatch ruins your sleep is still a mystery, but scientists suspect the immune system is involved. Messed up, beneficial bacteria can be pushed aside by more aggressive microbes, which attack the intestinal wall and spark an inflammatory response.

Don’t panic—inflammation is a crucial part of our immune system, helping us fight off viruses, harmful bacteria, and recover from injuries. The problem? Most of us suffer from chronic inflammation, and our immune reactions are often a bit too dramatic. If inflammation hits organs like the lungs, it can even impact breathing at night, boosting the risk of serious issues like sleep apnea.

All these gut-sleep connections could revolutionize the way we tackle sleep disorders. In the future, instead of turning straight to sleeping pills, perhaps we’ll have personalized diets tailored to our microbiome analysis. But even today, you can help your sleep quality by sticking to some simple rules: avoid night shifts, and above all, keep regular mealtimes with plenty of tryptophan and fiber. Quite possibly the best way to guarantee restful, cozy nights snuggled into your pillow.