Increasing Evidence That the Human Microbiome Plays a Major Role in Health

We've known for more than a century that we are colonized by bacteria and that a few species benefit our health by synthesizing important vitamins and amino acids, degrading toxins, and helping digest plant material. However, we've assumed that most species that live on or within us don't affect our health. An explosion of research is changing this view radically. We now know that our 13 trillion human cells coexist with 130 trillion bacterial cells. And, our 20,000 human genes coexist with 5 million to 8 million bacterial genes — what is called the “microbiome” or the “second human genome.”

Previously, the microbiome was linked to obesity (NEJM JW Gen Med Jan 2 2007), inflammatory bowel disease (NEJM JW Gen Med Jun 19 2008), psoriasis, nona…