(NBC NEWS) -- Most experts agree breast milk offers the best nutrition for young babies.
It is so precious that some over-productive mothers can sell their extra supply online to other parents, but that can lead to safety issues.
Investigators at Nationwide Children's Hospital in Ohio examined samples of breast milk purchased over the internet and found a troubling list of extra ingredients.
Out of 101 samples purchased online, three-quarters were contaminated with potentially dangerous bacteria. The longer it took to ship, the more bacteria was found in the samples.