You might not know this, but your body produces a whole bunch of antibacterial compounds, one of which is lactoferrin. It’s found in breast milk and mucosal substances such as tears and saliva. Lactoferrin hasn’t really been investigated as a medical antibiotic because many disease-causing bacteria (e.g., E. coli) also live on (and in) people as harmless commensals, and consequently, have evolved resistance to lactoferrin. However, a new paper suggests that some lactoferrin might kill these pathogens.
The authors found that people with a single amino acid change in lactoferrin “were more likely to develop traveler’s diarrhea (67% vs. 33%; relative risk [RR], 1.4; 95% CI, 1.2-1.7; P<.001), to have diarrhea with a pathogen identified (RR, 1.3; 95% CI, 1.1-1.6; P=.03), and to have a marker of intestinal inflammation in stool specimens (blood, mucus, or white blood cells; 52% vs. 38%; P=.036)." What particularly interesting is that this effect is found only for women, not men. I have no idea why that would be, but the authors suggest that it "may relate to the fact that lactoferrin expression is regulated differently in females than males, owning to the well-characterized estrogen-responsive elements in the DNA sequence" (which means they don't really know either).
It's pretty amazing that one itty-bitty nucleotide change can do all that. It will interesting to see how this polymorphism maps onto North American populations. Hopefully, someone is also going to do some good population genetics and look for selection at this gene.