Early-Life Iron Exposure Influences Long-Term Gut Microbiota Recovery After Intestinal Dysbiosis

Host-microbiota interactions during the neonatal window of opportunity have gained significant interest as factors influencing long-term health. Factors such as nutrient availability may shape the microbial community, and iron is no exception to this rule. Although the use of iron supplementation is widespread during infancy, this micronutrient is known to have profound effects on gut microbiota. This study aimed to determine how early-life iron supplementation shapes gut microbiota composition and whether it influences recovery from gut dysbiosis later in life. Three-week-old female C57BL/6 mice were fed an iron-excess diet for five weeks during the critical period of microbiota establishment. After a two-week washout period to normalize luminal iron content, dysbiosis was induced using either dextran sulfate sodium-induced acute colitis or antibiotic treatment. Mice were then allowed an 8-week recovery period. Gut microbiota composition was longitudinally analyzed by 16S rRNA gene sequencing of fecal samples. Early-life iron supplementation induced durable alterations in gut microbiota composition, with differences persisting even after luminal iron normalization (β-diversity, PERMANOVA p < 0.01). At the endpoint, mice exposed to an iron-sufficient diet remained significantly more distant from their baseline compared to the excess iron group in both the dextran sulfate sodium (33% greater distance) and antibiotic (41% greater distance) models (both p < 0.05). Notably, this pattern was not observed when supplementation occurred in adulthood. In the dextran sulfate sodium model, mice that received an iron-sufficient diet during early life showed an expansion of the probiotic Ligilactobacillus murinus, which positively correlated with fecal succinate levels. Conversely, in the antibiotic-induced model, early-life exposure to an iron-sufficient diet was associated with a more pronounced dysbiosis characterized by a nearly two-fold-greater loss in α-diversity compared to 500 ppm mice (∆Shannon: 1.98 ± 0.22 vs. 1.02 ± 0.25, p < 0.01). These findings suggest that early-life iron supplementation influences long-term host-microbiota interactions and recovery from gut dysbiosis.