Lactoferrin safety and side effects

What trials have reported

Across published trials, oral bovine lactoferrin has generally been tolerated without serious adverse effects attributed to it. In the comparison against ferrous sulfate in pregnancy, gastrointestinal side effects were significantly less frequent on lactoferrin than on the iron salt.

The largest safety dataset comes from a trial in very preterm infants, which recorded 16 serious adverse events in the lactoferrin group against 10 in the control group. Two events in the lactoferrin group, one case of blood in stool and one death following intestinal perforation, were assessed as possibly related to the intervention. The trial was not designed to characterize rare harms, and that imbalance supports no conclusion in either direction.

The limit of that evidence

Most lactoferrin trials are small and short. A trial of a few hundred people over several weeks cannot detect an effect occurring in one person per thousand, or one appearing after two years. Absence of reported harm at that scale is weak evidence of safety rather than strong evidence, and it should be described as such.

Who should not take it

Supplemental lactoferrin is produced from cow's milk or whey. It is therefore unsuitable for anyone with a cow's milk protein allergy, and products vary in how much residual milk protein they carry. This is the clearest contraindication and the one most often missed, because lactoferrin is frequently described as an immune ingredient rather than as a dairy protein.

Lactoferrin binds iron, which is the mechanism it is taken for. Anyone managing an iron disorder in either direction, including hemochromatosis, has reason to raise it with a clinician before starting.

Evidence in pregnancy comes from trials that studied treatment of diagnosed iron deficiency anemia under supervision, which is not the same as general supplementation. Evidence for infants concerns clinical administration in hospital, not products bought and given at home.