Tired at Work, Wired at Night? This Could Be Why

There’s a surprising wrinkle to your circadian rhythms.

"Think in the morning. Act in the noon. Eat in the evening. Sleep in the night." –William Blake

Every night, as the sun goes down, your gut microbes switch to the evening shift. The microbes of the night start to procreate and bloom while others die down, changing the entire composition of the microbiome. The chemicals they secrete change, too, which contributes to your sleepiness.

Some of these chemical signals reach the hypothalamus, a part of your brain that helps you keep it together in times of stress. Most of these brain regions were named long ago for their physical attributes, not their function, and this is true of the hypothalamus, which is simply Greek for “under the thalamus.” It’s an inauspicious name for such an important part of the brain.

The hypothalamus takes input from your environment and responds with hormones to balance out any external stressors. If it’s cold outside, your hypothalamus makes you shiver, which warms you up. If it’s hot, it will make you sweat, which cools you down. Animals can adjust to a wide variety of conditions because of this resilience circuitry. Without it, we would collapse at the first sign of adversity.

Your hypothalamus also responds to internal stressors. If you get food poisoning, your hypothalamus orchestrates a rapid emptying of your gut. That is paired with acute anxiety and an urgent desire to find a toilet.

Your hypothalamus also responds to mental stress, and a crappy boss can make your hypothalamus order up a dose of the stress hormone cortisol. That starts a complex chain of events designed to help you fight or run. It diverts energy from your immune system to your muscles and puts you on top alert.

The problem is that we can neither fight nor run from our boss, so we stew in our own hormones, day after day. Our stress circuits are designed to last for the duration of a tiger attack, which is typically over in a few minutes, favorably or not. It is not meant to last for hours, let alone days or years.

Long-term stress can spill over into other bodily systems, including the gut and the brain. Because stress takes energy away from your immune system, pathogens can sneak in and infect your tissues. That’s why people under continuous stress tend to get sick more often.

Your Body's Master Clock

Here’s the interesting wrinkle: Your hypothalamus also contains the body’s master clock. The hormones that stress you out are also the ones that wake you up in the morning.

Cortisol shoots up at first light, getting you out of bed and ready to deal with the tigers or bosses that rule our days. We tend to think that all stress is bad, but a little spritz of cortisol is just what you need to brave the world before you grab your morning coffee.

This moderate level of stress diminishes throughout the day, finally petering out around bedtime. So, stress and normal daily rhythms are braided together.

Nature loves to recycle anything that works. If a little cortisol can wake people up, then just dial it up to 11 for hyper-awareness of dangerous situations. And this is how your circadian rhythms came to be linked to your stress circuits.

Circadian Rhythms of Gut Microbes

Amazingly, the microbes that rule your gut also have circadian rhythms. Even though the sun doesn’t shine down there, in the morning, your microbes are eagerly awaiting breakfast, and, at night, they like to take a breather. So that late-night snack profoundly affects your gut microbes, with knock-on effects throughout the night and into the next day.

Getting out of synch with your microbes puts you at risk for sleepless nights and groggy days. Your gut and your hypothalamus are as tightly wired as your stress and circadian rhythms. So expect all of them to be affected if you have a lousy microbiome, bad sleep patterns, or too much stress.

And that’s just what Tofani et al. of University College Cork found in a recent study. They used mice to study the effect of the microbiome on stress and circadian rhythms.

Mice are awesome for this kind of study because you can raise them in a germ-free environment. To know what microbes are doing, it’s revealing to see what happens without them. They, along with researchers going back to Noriyuki Sudo, have found that germ-free mice have exaggerated levels of stress hormones. That tells us that microbes help to moderate stress reactions, which is an amazing amount of power to delegate to mere microbes.

Furthermore, they found that an unbalanced microbiome can disrupt our circadian rhythms. They identified one bacteria in particular, L. reuteri, that seems to settle the gut down and produce smooth circadian rhythms.

The researchers say their study offers “compelling evidence that the microbiota regulates stress responsiveness in a circadian manner and is necessary to respond adaptively to stressors throughout the day.”

That’s because a healthy gut microbiome plays well with your immune system and can actually lower stress levels via the gut-brain connection. The hypothalamus senses the satisfaction of the immune system and sends an all-clear signal, dialing down the secretion of cortisol.

Taking Care of Your Gut Microbes

And, so, taking care of your gut microbes can help you sleep better at night and deal with stress better during the day.

So, how do you take care of your gut microbes? Sadly, two wonderful comestibles, spirits and sweets, are not your friends because they promote a leaky gut. But your microbes love prebiotic fiber.

Prebiotics are largely composed of complex sugars that zip through our small intestines unscathed in order to feed microbes in the colon. That’s where the bulk of your microbes live, and they produce healthy substances like butyrate when they consume fiber. Butyrate is both a medicine and a food, healing and feeding the cells lining your gut. Surprisingly, butyrate can travel all the way to the brain, where it promotes the health and growth of nerve cells as well.

So, give your microbes a break and eat foods with fiber. And don’t feed the night shift. Like gremlins, they can get monstrous when fed after midnight. You’ve been warned.

References

Tofani, Gabriel S. S., Sarah-Jane Leigh, Cassandra E. Gheorghe, Thomaz F. S. Bastiaanssen, Lars Wilmes, Paromita Sen, Gerard Clarke, and John F. Cryan. “Gut Microbiota Regulates Stress Responsivity via the Circadian System.” Cell Metabolism. (November 5, 2024).