PTSD

Why Some People Develop PTSD After Trauma and Others Don't

This is an early field with small studies, and it's worth saying so before the findings. Post-traumatic stress disorder can follow a life-threatening experience, but most people who go through one never develop it. That difference is the interesting question, and it's the one the gut research has been built around. Instead of comparing patients against people who've had easy lives, these studies compare them against others who survived the same kind of event.

A comparison designed to isolate one thing

Researchers recruited 18 people diagnosed with PTSD and 12 people who'd experienced significant trauma without developing it. Everyone gave a stool sample, and PTSD symptoms were scored using a standard clinician-administered scale.

Overall bacterial variety was similar between the two groups, which rules out the simplest explanation.

What differed was three specific phyla, meaning three broad branches of the bacterial family tree: Actinobacteria, Lentisphaerae and Verrucomicrobia. Lower total amounts of these three were associated with having PTSD. A statistical model using them alone identified PTSD status with an error rate of about 31%.

The amount also tracked with severity. The less of these three bacteria a person had, the higher their symptom score.

Source: The Microbiome in Posttraumatic Stress Disorder and Trauma-Exposed Controls: An Exploratory Study

A finding that points back to childhood

One detail in that study is worth pulling out, because it suggests when these differences might arise.

People who'd experienced trauma in childhood had lower levels of two of the three, Actinobacteria and Verrucomicrobia. That held regardless of whether they'd also been through trauma as adults.

Childhood trauma is already known to raise the risk of developing PTSD later. So this offers a possible thread connecting the two. Early adversity may shape the gut community in ways that persist, and that community may then influence how someone's body responds to a later traumatic event.

All three of these bacterial groups are involved in regulating inflammation and immune function, which is a plausible route to the brain.

Where the research currently stands

Three human studies have been done, and a review pulled them together.

All three found differences between people with PTSD and trauma-exposed comparison groups. They did not find the same differences. One reported lower diversity in PTSD while the others didn't. The specific bacteria named varied from study to study, partly because the studies worked at different levels of the family tree.

A separate study found four genera, including Mitsuokella and Odoribacter, that were higher in the PTSD group and tracked with symptom severity.

A third looked at people with liver cirrhosis, comparing those who also had PTSD against those who didn't. The PTSD group had less of two fibre-fermenting families, the Ruminococcaceae and the Lachnospiraceae, and more of the bacteria that tend to expand when those decline.

So the honest summary is that something is consistently different, and nobody has yet pinned down what.

Source: Gut microbiome differences in individuals with PTSD compared to trauma-exposed controls: a systematic review

The direction problem

One question sits underneath all of this, and none of these studies can answer it.

PTSD changes sleep, appetite, activity and stress hormone levels. Each of those alters gut bacteria on its own. So a difference measured after diagnosis could be a consequence rather than a contributor.

The childhood trauma finding is the strongest hint that at least part of it comes first, since those bacterial differences were present in people who hadn't gone on to develop PTSD.

Settling it would need people tracked from before a traumatic event, which is difficult to arrange and hasn't been done.

What this means for you

PTSD responds well to trauma-focused therapy, so a doctor or a therapist trained in it is the right first step. In addition, the studies above suggest the bacteria that separate people who develop PTSD from those who don't are ones involved in regulating inflammation, which makes the gut a genuine part of the resilience picture. A varied, plant-rich diet supports the same gut bacteria this research ties to a lower probability of PTSD after trauma. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.