What does lactoferrin do?

Everything below follows from one piece of chemistry: lactoferrin holds iron, and holds it tightly. The functions attributed to the protein nearly all begin there, and they have been demonstrated at very different levels: some in a purified protein, some in human cells, some in piglets, some in a tube of bacteria. The level is the useful part, so this page sorts by it rather than listing functions flat.

The iron job, and where it was measured

Lactoferrin is most often described as the protein that carries iron from milk into a nursing infant. It is the dominant iron-binding component of human milk, and receptors for it have been reported in the brush-border membrane of the infant intestine, so the description is reasonable. The quantitative work behind it was done in pigs.

Gíslason and colleagues isolated living enterocytes from suckling piglets 6 to 20 days old, labeled porcine lactoferrin with iodine-125 and measured binding at 4 °C. Scatchard analysis gave an apparent dissociation constant of 2 x 10^-6 M, with a standard deviation of 0.6 x 10^-6, matching what the same group had found earlier in isolated membrane vesicles. Bovine lactoferrin competed for the site. Porcine transferrin, which also carries iron, did not, so the site is specific to lactoferrin rather than to iron-carrying proteins in general. Warmed to 37 °C, the cell-associated label reached almost five times what the cell surface could hold, which the authors read as continuous binding followed by the protein being taken inside.

Their own title describes the piglet enterocyte as a model for studying absorption, and their abstract says lactoferrin has been "suggested to play a key role" in human infants. Three decades on, that is still where the receptor work sits. Liao and Lönnerdal traced how its expression is controlled in a human colon cancer cell line and in mouse small intestine. Cooper and colleagues fed milk containing recombinant human lactoferrin to pigs and found fewer eosinophils in the duodenum, under a title saying the receptor "may mediate" it. The binding between lactoferrin and human intelectin-1, the protein proposed as the receptor, was demonstrated with recombinant proteins in a tube.

None of that makes the mechanism wrong, and the agreement across four studies in different preparations is real support. It does mean the familiar sentence about lactoferrin helping the body absorb iron rests on animal and cell work, and that nobody has yet measured the receptor doing its job in a living human. Whether swallowing the protein changes iron status in people is a separate question with its own trials, covered on lactoferrin for iron deficiency anemia.

What has been measured in people

Two things, and they sit at opposite ends of the protein's life.

The first is where it comes from and where it goes. Bainton's immuno-electron microscopy of human neutrophils assigns a marker protein to each granule population, and lactoferrin is the protein by which the specific granule is identified. Neutrophils moving into inflamed tissue carry those granules with them and empty them there. A working clinical assay rests on it: the protein turns up in stool in proportion to neutrophil traffic, which is the basis of the fecal lactoferrin test and the reason a laboratory can sell it. Measured against endoscopy, its sensitivity for active disease is about 0.82. The page on what fecal lactoferrin is follows the analyte back to the granule.

The second is the supply side, and it produced a null result worth stating plainly. Shashiraj and colleagues recruited 100 anemic and 100 nonanemic mothers at a New Delhi teaching hospital and followed them for six months, 102 of them to the end. Milk lactoferrin fell significantly between day 1 and 14 weeks in both groups, P<0.001. Hemoglobin, total iron binding capacity, transferrin saturation, serum iron and serum ferritin showed no correlation with milk lactoferrin at day 1, at 14 weeks or at six months. So an anemic mother's milk carries as much lactoferrin as anyone else's, and the amount an infant receives tracks the stage of lactation instead. That decline is the same one lactoferrin concentration records from a different method in a different country, which is useful cross-validation between two studies twelve years apart.

Why this page carries no grade

The evidence scale used elsewhere on this site rates claims about effects in people, and it would be a category error here. A receptor binding constant measured in a piglet is not a weak clinical trial. It is not a clinical trial at all, and putting a clinical grade on it would flatter the measurement and tell a reader nothing true. The table above does the job a grade would do, by naming the preparation instead.

Where a function has been carried as far as a clinical outcome, it has its own graded page. Growth inhibition in culture is graded Laboratory only on lactoferrin's antibacterial action. Adding the protein to antibiotics for Helicobacter pylori is graded Supported on pooled trial data. Its use in COVID-19 is graded Not supported, which is a stronger statement than untested. The benefits review carries the rest, including the claims for which no adequate human trial exists.