A Systematic Review and Meta-Analysis on the Effects of Probiotic Species on Iron Absorption and Iron Status

Systematic review with meta-analysis of human studies assessing probiotic species and iron absorption or iron status. Across the included studies, participants were mostly healthy adults, especially women of childbearing age, with additional studies in pregnant women, children, and people with diabetes or iron deficiency anemia; 15 studies contributed 950 active-arm participants overall, and 8 Lp299v studies with 122 subjects were pooled for iron absorption.

The review evaluated probiotic supplementation across 15 human studies, with a focused meta-analysis of Lactobacillus plantarum 299v (Lp299v) in 8 studies. Regimens varied widely by species, dose, and delivery, including milk, yogurt, powder, capsules, fermented foods, and meal-based carriers, with treatment durations ranging from 8 weeks to 6 months. Reported examples included L. casei 431 at 5 × 10^8 CFU/day, L. acidophilus at 1 × 10^7 CFU or 2 × 10^9 CFU, and multi-strain probiotic combinations containing Lactobacillus and Bifidobacterium species.

Lp299v consistently improved non-heme dietary iron absorption and was the only probiotic species with pooled evidence supporting this outcome. All 8 absorption studies reported a statistically significant increase, and the meta-analysis showed a pooled standardized mean difference of 0.55 (95% CI 0.22-0.88, p = 0.001). In contrast, iron-status markers did not improve consistently: only 1 study found better serum iron with Lp299v, while ferritin, hemoglobin, hematocrit, sTfR, and TIBC were generally unchanged or inconsistent. Overall, evidence for probiotic species other than Lp299v remains unknown.

The evidence base was small and heterogeneous, with half of the studies enrolling fewer than 30 participants and interventions varying substantially by species, dose, delivery vehicle, and duration. Most samples were from high-income settings and were demographically narrow, often healthy white European women, which limits generalizability. Iron-status outcomes were sparse and inconsistent, and long-term clinical effects were not established.