Do you know how many human cells make up a fully grown adult body? Approximately 37.2 trillion.
Twelve zeros—an amount that I can’t really fathom. Each and every one of them work together to allow you to go about your daily life and to read this blog post.
Now take that 37.2 trillion, and multiply it by three. That gives you 111.6 trillion, which is the approximate number of bacteria living on or inside of you at this very moment. You also have a bunch of other small organisms tagging along, such as archaea, fungi, and viruses—which aren’t all bad! This group of organisms that you lug around every day outnumber your actual human cells at least three to one—some estimates suggest a ratio of up to 10 to one. This large collection of microbes is called your microbiome, and it’s not as horrifying as it might seem.
Now, it’s important to know that a bacterial cell is far smaller than a human cell, so you can’t attribute the majority of your weight to freeloading single-celled organisms. In fact, if you were to combine all of the bacteria on and inside your body, they would only weigh about three pounds—about as much as your brain.
What’s even cooler than the sheer number of bacteria that make up your microbiome is their diversity. In my first-year biology class, I was told that the bacteria under your armpit compared to those on your foot are as different as the organisms in a jungle compared to those in a desert. Additionally, no two people’s microbiomes are identical, even in identical twins. This is because each person has a different life experience, and with new experiences come new bacteria that contribute to your microbiome.
Considering the amount and diversity of these microbes, answering the questions of what they do and why humans carry around these extra three pounds becomes quite complex. Recent research proposes that the microbiome plays essential roles in digestion and the regulation of your immune response, while also influencing other things, like your brain and behaviour.
Some of this research is being conducted here at Carleton by science professor Edana Cassol. Cassol is investigating how the bacteria in the human body and their by-products may influence the immune response. In terms of how these bacteria regulate your immune system, there is mounting evidence in support of a hypothesis called the “hygiene hypothesis.”
This hypothesis proposes that as levels of hygiene increase, such as in our hyper-sterile Western society, so does the risk of developing an allergic or autoimmune disease. Although one must be cautious when assigning a causal relationship, there is an abundance of support for this theory in both animal and human studies.
For example, a 2004 study showed that children who lived on a farm or attended a daycare when they were young, had lower incidents of eczema, an allergic hypersensitivity of the skin. The main idea behind the hygiene hypothesis is that bacteria are necessary for our health, and the only way to obtain them is through interacting with the environment.
The take-home message here is to lay off the Lysol wipes and appreciate all that the bacteria in your body do for you. Although most of their roles are still being researched, such as how the bacteria in your gut may influence your mood, it’s important to understand that not all bacteria are our enemies.
