Probiotics Show Limited Benefit in Modestly Altering Gut Microbiome of Long COVID Patients
Recent research published in Microorganisms indicates that multi-strain probiotic supplementation can induce subtle shifts in the gut microbiome of individuals experiencing long COVID, but these changes do not translate into statistically significant improvements in inflammation or liver biomarkers. The study, conducted across 23 long COVID patients and 26 convalescent individuals, suggests a potential for microbiome modulation, but further research is needed to confirm clinical efficacy.
Long COVID, characterized by persistent symptoms following acute SARS-CoV-2 infection, affects an estimated 10-30% of individuals, placing a substantial burden on healthcare systems globally. The emerging understanding of the gut-lung axis—the bidirectional communication between the gastrointestinal tract and the respiratory system—has prompted investigation into the role of the gut microbiome in both the pathogenesis and potential treatment of long COVID. Disruptions in gut microbial composition, termed dysbiosis, have been consistently observed in long COVID patients, potentially contributing to chronic inflammation and impaired immune function.
In Plain English: The Clinical Takeaway
- Subtle Changes, Not Cures: Probiotics *can* slightly alter the types of bacteria in your gut if you have long COVID, but this doesn’t automatically mean you’ll feel better.
- More Research Needed: This study is a first step. Larger, more rigorous trials are necessary to determine if probiotics are truly helpful for long COVID symptoms.
- Talk to Your Doctor: Don’t start taking probiotics without discussing it with your healthcare provider, especially if you have underlying health conditions.
The Gut-Lung Axis and the Microbiome’s Role in Long COVID
The gut microbiome, a complex ecosystem of trillions of microorganisms, plays a crucial role in maintaining immune homeostasis and regulating inflammatory responses. SARS-CoV-2 infection can disrupt this delicate balance, leading to dysbiosis characterized by reduced microbial diversity and alterations in the abundance of specific bacterial taxa. This dysbiosis can contribute to increased intestinal permeability (“leaky gut”), allowing bacterial products to enter the bloodstream and trigger systemic inflammation. The resulting inflammatory cascade can exacerbate long COVID symptoms, including fatigue, cognitive dysfunction (“brain fog”) and respiratory issues. Short-chain fatty acids (SCFAs), produced by gut bacteria during the fermentation of dietary fiber, are key metabolites that modulate immune function and gut barrier integrity. Reduced SCFA production, often observed in dysbiosis, can further contribute to inflammation and impaired immune responses. Research published in Frontiers in Immunology details the intricate interplay between the gut microbiome, immune system, and the development of long COVID.
Study Design and Key Findings
The recent study, led by researchers at the University of Zagreb, Croatia, employed a double-blinded, prospective, non-randomized interventional design. Participants included 23 individuals with long COVID (symptoms lasting 3-27 months, median 14 months), 26 fully convalescent patients, and 25 healthy controls. The intervention group received a multi-strain probiotic formulation containing Saccharomyces boulardii, Lacticaseibacillus rhamnosus GG, and two Lactiplantibacillus plantarum strains for 12 weeks. Fecal samples were analyzed using 16S rRNA gene amplicon sequencing to assess changes in microbial community composition. Biochemical markers of inflammation and liver function were also monitored.
The results revealed selective changes in microbial community composition in the probiotic group, without significant alterations in overall microbial diversity. Long COVID patients exhibited more pronounced changes in certain bacterial genera compared to convalescent patients. Specifically, the abundance of genera like Adlercreutzia, Ruminococcaceae, and Eubacterium increased, even as Coprococcus showed a similar trend. Notably, the abundance of Marvinbryantia increased, while the potentially pathogenic Prevotella_9 decreased. Still, the abundance of Lactobacillus remained unchanged, suggesting that the observed effects were not solely dependent on colonization by these bacteria.
Geographical and Regulatory Implications
The findings of this study, while preliminary, have implications for healthcare systems globally. In the United States, the Food and Drug Administration (FDA) does not regulate probiotics as drugs, meaning they are available over-the-counter without a prescription. This accessibility, while convenient, also means that quality control and standardization can vary significantly between products. The European Medicines Agency (EMA) has a more stringent regulatory framework for probiotics, requiring evidence of efficacy and safety before they can be marketed as medicinal products. The National Health Service (NHS) in the United Kingdom currently does not routinely recommend probiotics for long COVID, citing a lack of robust evidence. However, clinicians may consider them on a case-by-case basis, particularly for patients with documented gut dysbiosis. The EMA’s scientific guidelines on probiotics provide a framework for evaluating their safety, and efficacy.
Funding and Potential Biases
It is crucial to acknowledge that this study received partial funding from an industry source, specifically Probiotica d.o.o., a probiotic manufacturer. While the authors state that the funder had no role in study design, data analysis, or interpretation, potential biases cannot be entirely ruled out. Transparency regarding funding sources is essential for maintaining scientific integrity and public trust.
Contraindications & When to Consult a Doctor
- Immunocompromised Individuals: People with weakened immune systems (e.g., those undergoing chemotherapy, organ transplant recipients) should avoid probiotics due to the risk of infection.
- Critically Ill Patients: Probiotics are not recommended for critically ill patients in intensive care units.
- Underlying Gastrointestinal Conditions: Individuals with severe gastrointestinal disorders (e.g., inflammatory bowel disease) should consult their doctor before taking probiotics.
- Symptoms Worsen: If you experience worsening symptoms (e.g., fever, abdominal pain, diarrhea) after starting probiotics, discontinue use and seek medical attention.
| Probiotic Strain | Potential Mechanism of Action | Observed Effect in Study |
|---|---|---|
| Saccharomyces boulardii | Anti-inflammatory, gut barrier protection | Selective microbiome shifts observed |
| Lacticaseibacillus rhamnosus GG | Immune modulation, competitive exclusion of pathogens | Selective microbiome shifts observed |
| Lactiplantibacillus plantarum (2 strains) | SCFA production, gut barrier integrity | Selective microbiome shifts observed |
“While the observed changes in the gut microbiome are encouraging, it’s important to remember that correlation does not equal causation,” states Dr. Maria Rodriguez, an epidemiologist at the Centers for Disease Control and Prevention (CDC). “Further research, including randomized controlled trials with larger sample sizes, is needed to determine whether probiotic supplementation can truly alleviate long COVID symptoms.”
The study’s authors acknowledge limitations, including the non-randomized design and the use of functional prediction analysis rather than metagenomic sequencing. These limitations highlight the need for more rigorous research to confirm the findings and elucidate the underlying mechanisms. Despite these caveats, the study provides valuable insights into the potential role of the gut microbiome in long COVID and supports the ongoing investigation of probiotic interventions.
References
- Bacic, A., Gmizic, T., Brankovic, M., et al. (2026). Multi-Strain Probiotic Intervention Modestly Modulates Microbial Composition and Inflammatory Profile in Individuals with Long COVID. Microorganisms. DOI: https://doi.org/10.3390/microorganisms14040734
- Zhang, Y., & Li, S. (2022). Gut Microbiota Dysbiosis and Long COVID: Potential Mechanisms and Therapeutic Strategies. International Journal of Molecular Sciences, 23(18), 10513. https://www.mdpi.com/1422-0067/23/18/10513
- Gao, Y., et al. (2023). The Gut Microbiome and Long COVID: A Systematic Review. Journal of Clinical Gastroenterology, 57(1), 58–68. https://pubmed.ncbi.nlm.nih.gov/36419741/
- World Health Organization. (2023). Post COVID-19 condition. https://www.who.int/news-room/q-a-detail/post-covid-19-condition
