Lactoferrin is a supplement in the immune-boosting arsenal. It is a versatile substance found in mother's milk that plays an important role in the immune system response. Though human colostrum ("first milk") has the highest concentration, followed by human milk, then cow's milk, lactoferrin is found throughout the human body. It can help promote beneficial bacterial flora growth in the intestines. So by adding it to your regimen, you powerfully support both your immune health and your GI tract at the same time.