Schizophrenia's surprising link to the gut

What's in your tummy might affect what's in your head.

  • For decades, researchers have tried in vain to answer the question: What causes schizophrenia?
  • At the same time, we've developed a growing understanding of how intimately linked the bacteria in our gut and our brains are.
  • New research shows that schizophrenics have vastly different microbiomes, potentially uncovering a cause of — and maybe a future cure to — schizophrenia.

Researchers have tried to pin down what exactly has to happen for schizophrenia to rear its ugly head, but to little avail. We know there are changes in the brain, we know that there's some genetic component, but the real, root cause of schizophrenia remains mysterious to us.

However, a new study published in the journal Science Advances on February 6 has, at the very least, given us another clue to unraveling the origin of schizophrenia, and it's a rather unexpected one: the gut.

The brain in your stomach

We've known for some time that the gut and brain are deeply connected — so much so, your gut is often called your second brain. In terms of how we think, feel, and behave, the brain gets all the attention. It is the central nervous system, after all. But we too often ignore the impact that the peripheral nervous system has on us. And, out of all the nerve cells distributed throughout the body in our peripheral nervous system, the gut is particularly dense with 100 million neurons.

Why do our guts need these neurons? Well, part of it is that digestion is a complicated procedure, and it's much easier to outsource that job to a dedicated workforce of neurons. But our gut also does a bit more than simply grind up and digest what's inside our stomach and intestine. It talks to it.

The bacteria in our gut, collectively known as our microbiomes, do a lot of work for us. They help digest food and fend off disease, and, in return, we give them a home in our dark, warm, and damp interior — perfect for bacteria. So, if we want to be healthy, our microbiome needs to be healthy. When things are going well in our microbiome, we feel normal. The bacteria species in our guts pump out neuroactive chemicals, among them serotonin and dopamine, that get picked up by our peripheral nervous system and sent to our brains. When there's something wrong in our guts, we feel it in our brains.

Researchers have found that this effect is more profound than one might think. Prior research has shown that anxiety and depression in our brains also have a corresponding change in our guts: anxious and depressed people have different microbiomes. Now, researchers have shown similar findings for schizophrenics.

An artist's depiction of the microbiome. In our guts are trillions of bacteria, each of which does important work for our bodies and minds. Image source: Shutterstock

How schizophrenics have different guts than healthy patients

During the study, Peng Zheng and colleagues examined the fecal matter from a sample of schizophrenics and compared them with those from healthy controls. They found that schizophrenics had strikingly low diversity of bacterial species from the Lachnospiraceae and Ruminococcaceae families, species that are normally found in abundance. In contrast, species from the Veillonellaceae family were increased in schizophrenic patients. This difference is so stark, in fact, that the fecal matter samples alone could be used to predict whether a person was schizophrenic or not.

To extend this finding, Zheng and colleagues took these fecal matter samples and transplanted them in mice — some mice received fecal matter from schizophrenics, and some from the healthy subjects. By receiving fecal matter transplants, the mice also received a dose of the donor's microbiome.

It's difficult to accurately assess whether a mouse is behaving in a way that corresponds with schizophrenia, but, over the years, researchers have characterized several behaviors that correspond to schizophrenia in mice. The researchers found that mice who received a fecal transplant from schizophrenics were more hyperactive and more easily startled, both of which are consistent in mice models of schizophrenia.

Altogether, these findings suggest that there is, indeed, a strong link between the gut microbiome and the schizophrenic brain, perhaps even a causal one, although more research is needed to definitively say. However, the researchers do note that events that change the microbiome are associated with schizophrenia, implying a connection does indeed exist:

In the context of these findings, several events shown to influence composition of the gut microbiome, especially during the microbiome's establishment/dynamic period in infancy — e.g., cesarean versus vaginal birth, breast versus formula feeding, or early life antibiotic treatment — have all been associated, to some degree, with risk or onset of [schizophrenia].

So, is curing schizophrenia a simple matter of fixing the microbiome of its victims? Does the origin of schizophrenia lie within our guts? These questions can only be answered by further research. But nevertheless, the present study represents an exciting direction to explore, and one that will help to treat this terrible disease.

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