This is the beginning of a four-part series about the most interesting and troubling book I have read in many years, perhaps ever. I am hopeful that reading these columns will inspire you to do two specific things: ask different questions of your doctors, and share these columns with your friends and family. The book in question is Missing Microbes, How the Overuse of Antibiotics is Fueling our Modern Plagues, by Martin J. Blaser, MD. Dr. Blaser has devoted decades of careful, reproducible, and peer-reviewed research to this topic. He is currently the director of the Human Microbiome Program at New York University and has also worked at the National Institutes of Health and the Center for Disease Control. In his book, Dr. Blaser lays out a powerful and effectively irrefutable explanation of how overuse of antibiotics is the root cause behind a stunningly high number of our modern medical epidemics ranging from asthma to Celiac’s disease. To quote the New York Times, “The weight of evidence behind Dr. Blaser’s cautions about antibiotics is overwhelming.” I strongly recommend that you read this book. For those who do not, I will do my level best to convey its key points in this series.
The four parts of this series will review:
- the symbiotic relationship between humans and our resident bacteria;
- the detrimental effects of the overuse of antibiotics;
- the proposed steps to improve the situation; and
- the implications if we do not address this problem.
The story begins approximately 4 billion years ago when life began on earth. For three billion years, bacteria had the place all to themselves during which time they dramatically transformed the planet by creating soil and making oxygen. They also evolved. After three billion years of trial and error, they spawned the first multi-celled organisms. Evolution picked up speed at this point, leading to the first mammals 200 million years ago, primates 60 million years ago, and finally our genus, homo, 2.5 million years ago. The Earth is still completely dominated by bacteria. Not only do they vastly outnumber all other living things on Earth, they outweigh them as well. Understanding that we evolved from bacteria while living in a world filled with bacteria is vital to understanding how humans and our resident bacteria coexist.
Your body is comprised of approximately 30 trillion human cells and is home to more than 100 trillion bacteria cells. Thus, approximately 75% of the cells in your body are not you! In addition, with their lengthy evolutionary head start, bacteria cells are more biologically complex than human cells. As a result, over 99% of the genes within your body are not yours. I’m tempted to include a paragraph or two on the science of genes, but that would throw us off course. For our purposes, let’s consider genes to be the tool kit for the cell. The more genes a cell has, the more different types of biologic processes it can carry out.
During the entire time humans have been evolving, these bacteria, with their varied and their often-useful genes, have been within us. Since evolution selects against the inefficiencies of duplication of effort, our human and bacterial cells share the job of maintaining our existence. For example, our resident bacteria help to digest our food and to make vitamins and enzymes. They produce most of the chemicals in our bloodstream and also play a key role in regulating our blood pressure. Our bacteria also play two pivotal roles in our immune system; they fend off infection from pathogenic bacteria by crowding them out, and they help control the strength of our allergic responses. In exchange, we provide our bacteria with food, water, and a temperature-regulated home.
Humans acquire most of their resident bacteria, collectively their microbiome, in the first moments and months of life. In the womb, babies’ bodies are mostly bacteria free. This situation changes rapidly during a vaginal birth as the baby ingests and is coated with bacteria-rich amniotic fluid and placenta. Additional bacteria are also introduced via breast feeding and environmental exposure. By around six months of age, the composition of a child’s microbiome has been largely established for the long term. In an ideal case, her microbiome will include the full array of bacteria that the human body has evolved to depend upon. To the extent that some of these expected bacteria species are missing, a variety of problems, which I will discuss next week in Part II, can arise.
There are three primary ways in which the diversity of a child’s microbiome can become limited. These are:
- the child’s mother lacked certain species of bacteria to pass along;
- the child was born via C-section; and/or
- the child was given one or more courses of broad-spectrum antibiotics, particularly during the first six months of her life.
Since lack of bacterial diversity can persist for decades, managing a child’s health with a focus on her microbiome during these first critical months is vitally important. Strategies for this will be the topic of Part III.
It is becoming increasingly clear that the combined influence of the three factors listed above is dividing the population, particularly of developed countries, into two distinct categories, those with high bacterial diversity and those with low diversity. For example, a recent study in Europe found that 77% of people had an average of 800,000 bacterial genes in their microbiome and 23% had an average of 400,000, a reduction of 50%! As noted by Dr. Blaser, this large and growing population of people who lack the bacteria species that their bodies need is being disproportionately saddled with our “modern plagues.” I’ll discuss how and why next week.
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