Cow’s Milk Contamination of Human Milk Purchased via the Internet

BACKGROUND: The US Food and Drug Administration recommends against feeding infants human milk from unscreened donors, but sharing milk via the Internet is growing in popularity. Recipient infants risk the possibility of consuming contaminated or adulterated milk. Our objective was to test milk advertised for sale online as human milk to verify its human origin and to rule out contamination with cow’s milk.

METHODS: We anonymously purchased 102 samples advertised as human milk online. DNA was extracted from 200 µL of each sample. The presence of human or bovine mitochondrial DNA was assessed with a species-specific real-time polymerase chain reaction assay targeting the nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 5 gene. Four laboratory-created mixtures representing various dilutions of human milk with fluid cow’s milk or reconstituted infant formula were compared with the Internet samples to semiquantitate the extent of contamination with cow’s milk.

RESULTS: All Internet samples amplified human DNA. After 2 rounds of testing, 11 samples also contained bovine DNA. Ten of these samples had a level of bovine DNA consistent with human milk mixed with at least 10% fluid cow’s milk.

CONCLUSIONS: Ten Internet samples had bovine DNA concentrations high enough to rule out minor contamination, suggesting a cow’s milk product was added. Cow’s milk can be problematic for infants with allergy or intolerance. Because buyers cannot verify the composition of milk they purchase, all should be aware that it might be adulterated with cow’s milk. Pediatricians should be aware of the online market for human milk and the potential risks.