Iron deficiency and gut health are closely linked, and the relationship runs in both directions. Iron deficiency can affect the gut microbiome and intestinal barrier, while gastrointestinal (GI) disorders can reduce iron absorption and make deficiency harder to correct.
For healthcare professionals, the key issue is not only replacing iron but also understanding why deficiencies develop, how the gut is contributing, and how treatments might affect GI tolerance and adherence. In this article, we explore the mechanisms linking iron status and gut health, the impact of oral iron on the microbiome, and the current evidence for probiotics as an adjunctive strategy.
Iron deficiency anaemia is the most common nutritional deficiency in the world, affecting over 1.2 billion people. In the UK alone, it is estimated that 3% of men and 8% of women suffer from iron deficiency anaemia1. Several factors can cause iron deficiency, including2:
Symptoms of iron deficiency can overlap with other conditions but can include3:
People at higher risk of iron deficiency include menstruating women, pregnant women, infants and children, vegetarians and vegans, and patients with coeliac disease, inflammatory bowel disease, atrophic gastritis, or ongoing GI blood loss4.
Diagnosis usually relies on ferritin, haemoglobin, transferrin saturation, and the clinical context5. This is because ferritin can be misleadingly normal or high in inflammatory contexts6. In routine practice, treatment is based on identifying the cause and choosing oral or intravenous iron according to severity, tolerance, and expected absorption.
Absorption of iron occurs mainly in the duodenum and proximal jejunum, and depends on the form of iron, gastric acidity, hepcidin activity, and co-existing dietary factors7. Haem iron is generally more bioavailable than non-haem iron, while phytates, polyphenols, calcium, and inflammation can all reduce absorption.
This is where the gut microbiome becomes clinically relevant. Human studies suggest that selected probiotics may influence non-haem iron absorption, with Lactobacillus plantarum 299v (Lp299v) the most consistently studied strain. In a double-isotope crossover study in women of reproductive age, Lp299v increased non-haem iron absorption from an iron-supplemented fruit drink8. A 2019 meta-analysis of 15 human studies found that Lp299v significantly improved iron absorption overall, although evidence for broader iron-status outcomes was limited9. More recently, a 2020 study reported that Lp299v plus iron improved iron status and self-reported vigour more rapidly than iron alone10.
Nutritionally, this means that the management of iron deficiency should not focus on iron tablets alone. Attention to meal composition, supplement timing, and underlying gut pathology can improve outcomes in selected patients11.
Oral iron is effective, but it can produce GI side effects like nausea, abdominal discomfort, constipation, and altered bowel habits, all of which can lead to poor adherence12. Unabsorbed iron can also alter microbial composition, shifting the balance away from protective species and towards organisms that may be more pro-inflammatory or pathogenic13,14.
Human intervention studies support this concern, although the magnitude of effect varies by population and formulation. A 2023 secondary analysis of a double-blind trial in Cambodian women of reproductive age found that oral iron supplementation altered gut microbial composition15. Ferrous bisglycinate increased the relative abundance of Enterobacteriaceae, while ferrous sulfate was associated with an increase in the EPEC virulence gene bfpA. By contrast, a 2024 randomised trial in nonpregnant Australian women found no overall change in microbiome diversity or the abundance of common taxa after 21 days of ferrous fumarate16. These contrasting findings suggest that iron supplements' gut microbiome effects are context-dependent rather than universal.
More broadly, recent human work suggests that iron deficiency anaemia itself may be associated with gut dysbiosis and barrier dysfunction14,17,18. That matters clinically because oral iron side effects and dysbiosis can both affect adherence, particularly in patients with pre-existing GI symptoms or inflammatory bowel disease.
The short answer is yes. Inflammatory and structural gut disorders can reduce iron absorption through several mechanisms, including reduced mucosal integrity, altered acidity, hepcidin upregulation, bleeding, and malabsorption. Coeliac disease, inflammatory bowel disease, and other chronic enteropathies are classic examples, but more subtle gut dysfunction may also contribute to persistent low iron stores17,19.
Several studies suggest that the gut microbiome may play a role in iron status by influencing absorption, microbial competition for iron, and the composition of the intestinal ecosystem. In infants with iron deficiency anaemia, distinct microbial signatures have been reported, including enrichment of Enterobacteriaceae and Veillonellaceae and reduced Coriobacteriaceae20. In adults, higher iron intake has also been associated with dose-dependent shifts in microbiome composition, including changes in Proteobacteria and taxa linked with gut health21. Together, these findings support a microbiome-mediated contribution to iron homeostasis, although the clinical implications are still being defined.
This is especially true when oral iron response is poor. If ferritin and haemoglobin fail to improve as expected, clinicians should consider ongoing blood loss, inflammatory disease, untreated malabsorption, medication effects, and adherence issues before simply escalating supplementation17,19.
The idea that probiotics might support iron status is biologically plausible, but the evidence is still limited and strain-specific. A systematic review and meta-analysis of human studies found that Lactobacillus plantarum 299v significantly improved iron absorption, but this did not translate into consistent improvements in broader iron-status markers across studies9. A 2025 systematic review of prebiotics and probiotics in children and women of reproductive age also suggested possible benefits for fractional absorption and ferritin in some groups, but the certainty of evidence remained low to moderate depending on outcome22.
That distinction matters. Although the phrase ‘probiotics and iron absorption’ is increasingly common in the literature, current evidence does not support a blanket recommendation for probiotics as a treatment for iron deficiency. Some studies suggest potential benefits through improved luminal conditions, reduced inflammation, or enhanced mucosal function, but these hypotheses remain under investigation9,22–24.
Some human studies have explored whether probiotic administration may improve GI tolerance during oral iron therapy. One recent clinical study reported improved GI tolerability, treatment adherence, and some iron markers when a probiotic was used alongside oral iron, but this is still emerging evidence rather than established practice25. Overall, probiotics may have a future adjunctive role, but the current evidence base is not strong enough to recommend them routinely for improving iron status.
Iron deficiency and gut health influence one another, so effective management should address both iron replacement and underlying GI factors. Clinicians should consider the site and cause of impaired absorption, the presence of inflammation or GI disease, and the likelihood of tolerability problems before choosing a treatment strategy. If oral therapy is poorly tolerated or ineffective, alternative dosing strategies or intravenous iron may be appropriate depending on the clinical scenario. The emerging literature on the gut microbiome’s role in iron absorption and on microbiome-targeted support is promising but remains early-stage. For now, the message is simple: treat the deficiency, investigate the cause, and consider the gut as part of the treatment plan rather than a separate issue.
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