New biomarker links fibromyalgia and gut microbiome
Fibromyalgia is still diagnosed clinically, after other conditions are ruled out. New studies show raised neurofilament light chain in the blood of people with fibromyalgia, a marker of strain on nerve fibers. The gut enters the picture because dysbiosis may feed that strain, through inflammation and the vagus nerve.
How do fibromyalgia and the gut microbiome connect?
Fibromyalgia and the gut microbiome seem like two unrelated topics. Yet the gut talks to the nervous system directly, through the vagus nerve, inflammation and substances the bacteria themselves make. If that conversation breaks down, the effect can travel to the brain and the nerves, exactly where the new fibromyalgia marker now shows up.
Fibromyalgia has many causes, and the gut is not the only one. Still, it is one of the levers that may affect how much strain the nerves are under, and that strain is now measurable in blood. Fibromyalgia and IBS also overlap often, which makes the gut side hard to ignore.6
I've had a fibromyalgia diagnosis for two years, but for the last six months I've also been dealing with bloating and an irregular gut every day. Is that a coincidence, or could one be feeding the other?
It is less of a coincidence than you might think. Fibromyalgia and the gut microbiome communicate through the vagus nerve and inflammation, so a disrupted gut can feed the pain, and the link may run both ways. Bloating and an irregular gut can be part of the same mechanism as the fibromyalgia itself. It makes sense to look at them as one problem with a shared starting point.
Why is fibromyalgia usually diagnosed clinically?
Fibromyalgia diagnosis today rests on symptom criteria, painful points and ruling out other conditions, a purely clinical process. The doctor takes the history, checks pain at specific points and rules out rheumatoid arthritis, lupus and other conditions that look similar. The process can take years, especially when symptoms change in intensity from month to month.
A real biological marker would change this. It would give something measurable for a condition that, until now, has relied almost entirely on clinical judgment.
What do the new studies show about neurofilament light chain in fibromyalgia?
Neurofilament light chain (NfL) is a protein that supports the internal skeleton of nerve fibers. When a fiber is damaged, it releases fragments into the blood, and three recent studies found higher levels in people with fibromyalgia.2, 3, 4
- Neurofilament light chain (NfL)
- A structural protein of nerve fibers. When fibers are injured or under strain, fragments leak into the blood, where a sensitive test can measure them. It is already used as a marker in other neurological conditions.2
What the Bari team found
Ruggieri and colleagues measured plasma NfL in 33 women with fibromyalgia and 22 age-matched controls. Levels were clearly higher in the fibromyalgia group, regardless of how severe the disease was or how long it had lasted, and higher values went with weaker working memory and shorter sleep.2
In a larger follow-up in 2026, with 70 people with fibromyalgia and 55 controls, the same team again found higher NfL. This time, however, NfL did not track small fiber damage on skin biopsy, pain scores or cognitive tests. The only clinical link was with disability, so the authors read it as a marker of nervous system strain related to the overall disease burden.3
What the Oxford team found
A separate Oxford study measured serum NfL in 60 people with fibromyalgia, 61 with endometriosis, 24 with small fiber neuropathy and 30 healthy controls. Levels in fibromyalgia were raised and comparable with small fiber neuropathy, a recognized nerve condition, although they did not match how neuropathic the pain felt.4
The 2026 Bari study concluded that serum NfL is raised in fibromyalgia but is not linked to small fiber pathology or cognitive impairment, and suggested it as a possible marker of neuronal stress in chronic pain rather than a specific marker of nerve damage.3
How accurate is a blood test for fibromyalgia today?
NfL is not the only blood test under study. Researchers at Ohio State used surface-enhanced Raman spectroscopy on blood samples from 83 people with fibromyalgia and 54 people with other rheumatic conditions, such as rheumatoid arthritis, lupus and osteoarthritis. In that exploratory study, the method separated the groups with 100% accuracy.5
It is a different technology from NfL, and it still needs testing in larger, independent groups before it reaches routine use. Even so, it shows that an objective blood test for fibromyalgia is getting closer.
What mechanisms link gut dysbiosis to nerve strain?
Dysbiosis travels through several routes at once. Lipopolysaccharides, the vagus nerve, short-chain fatty acids, the stress axis and chronic immune activation together form a network that may end at the same place, the nerve fiber.
- Gut dysbiosis
The balance of gut bacteria shifts and the gut barrier loosens.
- Lipopolysaccharides in circulation
Fragments of bacterial walls cross into the blood more easily.
- TLR4 activation
Immune receptors recognize these fragments.
- Inflammatory cytokines
IL-6 and TNF-alpha rise.
- Neuroinflammation
Immune cells of the nervous system stay switched on.
- Nerve fiber strain
Fibers come under stress, the kind of damage NfL can capture.
A simplified chain built from separate lines of research, not from a single study.
The lipopolysaccharide and vagus nerve route
When the gut barrier loosens, lipopolysaccharides from bacteria such as Escherichia coli cross into circulation more easily, activate the TLR4 receptor and trigger the release of inflammatory cytokines. At the same time, vagal nerve fibers carry TLR4 receptors themselves, so they can sense bacterial signals directly and pass them to the brain, which may change how pain is processed.7 How a leaky barrier feeds this is explained in how to treat gut dysbiosis.
The short-chain fatty acid route
Gut bacteria such as Faecalibacterium prausnitzii make short-chain fatty acids, and in mice these fatty acids help keep microglia, the brain's immune cells, mature and balanced.8 When these bacteria decline, microglia may lose part of that steadying influence and stay in a state of low-grade inflammation. In people with fibromyalgia, serum butyrate and propionate levels also differed from controls.9 More on this species is in low Faecalibacterium prausnitzii.
| Route | What may change with dysbiosis |
|---|---|
| Gut barrier | Lipopolysaccharides cross into circulation more easily and activate TLR4, feeding inflammation. |
| Vagus nerve | The signal to the brain changes, which may affect how pain is processed. |
| Short-chain fatty acids | Fewer butyrate producers may leave microglia less regulated. |
| Stress axis | Dysbiosis may disturb cortisol rhythms and reinforce central sensitization. |
| Chronic immune activation | Ongoing IL-6 and TNF-alpha keep the nervous system on alert. |
Which bacteria have been linked to fibromyalgia?
No study yet links one specific bacterium directly to NfL levels in fibromyalgia, because the field is still young. There is something closer, though, an animal study that links the microbiome itself to nerve fiber damage.1
Cai and colleagues transferred gut microbiota from women with fibromyalgia into germ-free mice. The mice developed pain together with reduced skin innervation, the type of damage that NfL reflects in blood. After the researchers replaced that microbiota with a healthy one, the pain dropped substantially.1
Gut microbiota from people with fibromyalgia, but not from healthy controls, caused pain and immune and metabolic changes in germ-free mice that matched known changes in patients. A healthy microbiota largely reversed the pain.1
At the level of composition, the gut of people with fibromyalgia also looks different. In 77 women with fibromyalgia and 79 controls, several bacterial groups differed, the changes tracked clinical scores, and the microbiome alone could separate patients from controls in most cases.9 A 2025 study in 37 women found lower diversity, more SIBO with methane dominance, and more Akkermansia, Methanobrevibacter and Christensenellaceae.10 The pattern therefore goes beyond fewer protective bacteria, and each person's profile can differ.
After a course of antibiotics for a urinary tract infection last year, my fibromyalgia got a lot worse and I started reacting to foods I used to eat just fine. Could those be connected?
They could be. A course of antibiotics hits the microbiome hard, lowers some protective bacteria and leaves room for more inflammatory groups, the kind of changes linked to worse fibromyalgia and new food reactions. That timing deserves attention. Write down when the reactions started compared with the treatment, because it helps a lot with the next step.
Can a healthy gut microbiome improve fibromyalgia symptoms?
There are early human data. In the same study as the mice, an open-label trial of microbiota transplant in women with fibromyalgia went with less pain and better quality of life.1 Without a placebo group, though, the size of the effect is still uncertain.
A systematic review of 11 human studies found that probiotics and prebiotics showed promise for pain, cognitive symptoms and neuroinflammation in conditions relevant to fibromyalgia, although only some of the studies included people with fibromyalgia.11 Separately, a 2025 study described how the gut microbiota of women with fibromyalgia differs and how those differences relate to their symptoms.10
What does this mean in practice?
In practice, the link between fibromyalgia and the gut microbiome earns a real place in the conversation, as a mechanism with measurable effects. The same pattern of dysbiosis and a leaky barrier appears elsewhere in the body too, and the gut is often where it shows first.
The gut-brain axis carries this signal well beyond digestion. A structured plan for dysbiosis gives a clear order of testing and diet changes, as described in how long it takes to heal gut dysbiosis. In the clinics where I work as a scientific collaborator, the first step is usually simple, tracking gut symptoms and fibromyalgia together.
Frequently asked questions
It is a protein that supports the internal skeleton of nerve fibers. When fibers are damaged or under strain, fragments leak into the blood, and a sensitive blood test can measure them.2
Current studies show that the microbiome can influence pain and nerve changes, as one factor within a condition with many causes.1
Early studies suggest probiotics and prebiotics may help pain, cognition and mood in conditions relevant to fibromyalgia, but larger trials in people with fibromyalgia are still needed.11
Track both together for a few weeks to see if they move in parallel. From there, an appointment can check whether they belong to the same clinical pattern.
References
11 studies
- Cai W, Haddad M, Haddad R, et al. The gut microbiota promotes pain in fibromyalgia. Neuron. 2025.
- Ruggieri M, Paparella G, Clemente L, et al. Plasma neurofilament light chain in fibromyalgia: a case control study exploring correlation with clinical and cognitive features. Eur J Pain. 2025.
- Ruggieri M, Gargano CD, Paparella G, et al. Neurofilament light chain in fibromyalgia: correlation with central and peripheral nervous system dysfunction. Eur J Pain. 2026.
- Fundaun J, Kelleher E, Coxon L, et al. Serum neurofilament light chain in fibromyalgia: comparative evidence of neuronal injury across chronic pain conditions. Pain Rep. 2026.
- Bao H, Hackshaw KV, Castellvi SL, et al. Early diagnosis of fibromyalgia using surface-enhanced Raman spectroscopy combined with chemometrics. Biomedicines. 2024.
- Erdrich S, Hawrelak JA, Myers SP, Harnett JE. Determining the association between fibromyalgia, the gut microbiome and its biomarkers: a systematic review. BMC Musculoskelet Disord. 2020.
- Jia L, Lee S, Tierney JA, et al. TLR4 signaling selectively and directly promotes CGRP release from vagal afferents in the mouse. eNeuro. 2021.
- Erny D, Hrabě de Angelis AL, Jaitin D, et al. Host microbiota constantly control maturation and function of microglia in the CNS. Nat Neurosci. 2015.
- Minerbi A, Gonzalez E, Brereton NJB, et al. Altered microbiome composition in individuals with fibromyalgia. Pain. 2019.
- Lopez de Coca T, Muñoz-Almaraz FJ, Martinez-Blanch JF, Moreno L. Exploring gut microbiota alterations and their associations with clinical symptoms in fibromyalgia. Sci Rep. 2025.
- Dipalma G, Marinelli G, Ferrante L, et al. Modulating the gut microbiota to target neuroinflammation, cognition and mood: a systematic review of human studies with relevance to fibromyalgia. Nutrients. 2025.
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Cite this article
Prevedoros, T. (2026, September 6). New biomarker links fibromyalgia and gut microbiome. Gut Pathways. https://gutpathways.com/articles/fibromyalgia-and-gut-microbiome/
