Freshly purified fractions of lactoferrin from expressed human breast milk (Human Lf, black bars), or commercially-sourced bovine lactoferrin preparations (Bovine Lf, grey bars), as well as iron-saturated isoforms of each respective preparation (holo-Lf) were subjected to ICP-MS elemental analysis to enumerate the iron (Fe) ions associated with 100 μg of sample. Bars indicate mean values of at least three biological replicates +/−SEM. *P<0.0001, **P<0.001, *P<0.05, one-way ANOVA with Tukey’s post-hoc test, #P<0.05, unpaired Student’s t test.