Fe³⁺ · 80 kDa · transferrin family
Lactoferrin, graded by the evidence.
An iron-binding protein of milk and mucosal secretions, studied for sixty years and claimed for rather more than it has shown. Every claim on this site carries the strength of the evidence behind it.
Lactoferrin is a single-chain glycoprotein of roughly 80 kilodaltons, built from two similar lobes. Each lobe binds one ferric iron ion with a tenacity few biological molecules match, and holds it across a range of acidity that would strip most carriers. The protein occurs in milk, most abundantly in colostrum, and also in tears, saliva, nasal and intestinal secretions, and in the granules of neutrophils, where it is released at sites of inflammation.
Its best-characterized action follows directly from the iron binding. By sequestering free iron it denies an essential nutrient to bacteria that need it, which is where the antimicrobial reputation began. Subsequent work has described effects that do not depend on iron at all, including direct interaction with bacterial membranes and with host cell receptors.
What that means for a person taking a supplement is a separate question, and a much less settled one. The ledger below is this site's answer to it.
The claim ledger
The scale
- Established Supported by more than one adequately powered human trial, with findings that broadly agree.
- Supported Human trial evidence exists and points one way, but the trials are few, small, or narrow in who they studied.
- Preliminary Some human data, typically small, short, uncontrolled, or reported only as a secondary outcome.
- Laboratory only Demonstrated in cell culture or animal models with no adequate human trial. Frequently reported as though it were a clinical finding. It is not one.
- Insufficient Claimed, but without evidence adequate to assess it either way. Absence of evidence, not evidence of absence.
- Not supported Adequately powered human trials tested this and did not find the claimed effect. Strong evidence, pointing away from the claim rather than towards it.
How this site works
Every claim gets graded on the best available evidence, not the most recent study and not the most favorable one. A grade of Laboratory only is a description rather than a criticism: a great deal of genuinely interesting lactoferrin research has been done in cells, and reporting it as though it were a clinical finding is the error, not the research itself.
Where the honest grade is Insufficient, the page still gets written. Recording that nobody has run an adequate trial is useful, and it is information that is otherwise hard to find.
Figures carry their units and their source. Lactoferrin concentrations vary by more than an order of magnitude between human colostrum, mature human milk and bovine milk, and quoting a single number without saying which one it describes is the most common error in writing on this subject.
More on sourcing and method on the about page.