Oral iron supplementation can enhance the growth of pathogenic bacteria and inhibit the growth of beneficial bacteria. Supplementing, especially over-supplementing with iron, can cause GI dysbiosis and adverse effects.
During an active bacterial infection, the host (us) and the pathogen (bacteria) actually compete for iron. Wisely, the body shepherds iron from the circulation into storage in the event of an infection. This results in a decrease in serum iron with a subsequent decrease in erythropoiesis, which is an iron-dependent process. Iron also impairs immune cell functioning, potentially contributing to microbial virulence. (Pieracci 2005).
A case-control study of 300 subjects with H. pylori and 300 controls found that the mean serum iron in those infected was significantly lower, and ferritin was significantly higher in those infected with the pathogen (Kishore 2021).
In addition, iron in the gastrointestinal tract can promote the proliferation of pathogenic bacteria, including methane-producing species, which are significantly iron-dependent. An excess of GI methane can contribute to a slower GI transit, bloating, and constipation. Consuming oral iron beyond what the GI tract can absorb can enhance the growth of pathogenic bacteria while reducing the balance of beneficial bacteria (Bloor 2021).
For these reasons, it would be prudent to withhold iron supplementation during an active infection and avoid over-supplementing with iron at any time.
Bloor, Sarah R., Rudolph Schutte, and Anthony R. Hobson. "Oral iron supplementation—gastrointestinal side effects and the impact on the gut microbiota." Microbiology Research 12.2 (2021): 491-502.
Kishore, Gehna et al. “Association Between Helicobacter pylori Infection and Serum Iron Profile.” Cureus vol. 13,9 e17925. 13 Sep. 2021, doi:10.7759/cureus.17925
Nairz, Manfred et al. “Genetic and Dietary Iron Overload Differentially Affect the Course of Salmonella Typhimurium Infection.” Frontiers in cellular and infection microbiology vol. 7 110. 11 Apr. 2017, doi:10.3389/fcimb.2017.00110
Pieracci, Fredric M, and Philip S Barie. “Iron and the risk of infection.” Surgical infections vol. 6 Suppl 1 (2005): S41-6. doi:10.1089/sur.2005.6.s1-41