Trials of the Firstborn
It's not easy being the first kid in a family, but at least you get to inoculate your sibs.
The following is adapted from The Psychobiotic Revolution:
“In a big family the first child is kind of like the first pancake. If it’s not perfect, that’s okay, there are a lot more coming along.” —Antonin Scalia
In 1989, David Strachan wrote a letter to the British Medical Journal he titled “Hay fever, hygiene and household size”. In it, he described his analysis of 17,414 British kids born in March 1958. Looking at data on the kids 23 years later, he was able to analyze the incidence of hay fever, asthma and eczema — allergic diseases caused by an overactive immune system.
The immune cells of these sufferers are very sensitive, and they can freak out when they see an otherwise harmless pollen grain or friendly bacteria. They go into overdrive, inflaming tissues for no good reason. They secrete proteins called cytokines that summon more immune cells to the site of the inflammation. These new recruits freak out as well, spraying more cytokines in a frenzied feedback loop called a cytokine storm. Unless something can break the feedback loop, this can get nasty and even kill you with anaphylactic shock. It is friendly fire; you are, essentially, murdered by your own immune system.
Strachan found something very interesting about the data: when he tried matching the rates of allergies to other variables, he found one thing that correlated perfectly: the size of the household. The fewer the kids, the greater the allergies. And the firstborns were worse-off than their siblings. What was happening?
Strachan realized that each kid was being vaccinated by their older siblings. Early exposure to hand-me-down microbes somehow quiets the allergic reaction. They become immune tolerant: they learn to live and let live. The firstborns don’t have the luxury of a tested microbiota, typically passed down via sibling snot, to tutor their naïve immune system. That lack of education leads them to overreact when exposed to new microbes.
Tiny teachers
If the immune system is the student in this metaphor, the teachers must be the microbes. Warmly swaddled in mucus, your sibling’s microbiota is ready at a moment’s notice to pass on its life-lessons. A sneeze, a poke in the eye, a wet finger in the ear; these are just a few of the methods for inheriting bacteria from your clan. The firstborn misses out on many of these familial microbial anointments.
This observation became known as the “hygiene hypothesis”, and it had a dogma-busting impact on how people looked at bacteria. Rather than being pathogenic or at best marginally useful, a certain set of bacteria actually seem to be essential for the proper development of your body’s defenses. It is the job of these microbes to train your immune system, and without them, your system stays naïve and prone to overreaction. Critically, the training needs to happen at an early age. It is notoriously difficult to teach an old immune system.
As a result of the hygiene hypothesis, researchers started paying more attention to the good bacteria in and on the body. It is a world of mystery and wonder. We’ve since found that bacteria work with the immune system in your gut to add an extra layer of protection. Certain favored bacteria not only get along well with your own cells, they also give grief to pathogens. They compete with pathogens for food and slip them poison on a regular schedule. They have a surprisingly intimate relationship to the cells lining your GI tract.
The “skin” or epithelium of your gut mostly consists of absorptive cells called enterocytes. These do the major work of absorbing nutrients from your food and they’re tightly bound together by some tenacious proteins. The main point is to stop bacteria, which are swarming in your gut, from getting into your bloodstream. The binding of a gut lining is so tough that you can stuff sausage into it. Considering that this translucent tissue is just a few cells thick, it is remarkably resilient. And yet, in order to absorb nutrients, the cells need to be at least somewhat permeable. It’s a crazy balancing act.
Some of the absorption is simple; ions can be pumped directly through pores in the enterocyte membranes. Small molecules can get through the cracks between the enterocytes. Certain fatty molecules can “melt” right into the cells themselves. Other larger molecules may use complex molecular portals in the enterocyte membrane to escort them inside. These techniques allow you to take in nutrients, but they can be subverted by microbes as well.
Your gut, in other words, has the unenviable goal of making an impenetrable wall that is also permeable. It is the job of a pathogen to exploit the inevitable glitches that result from trying to reconcile these incompatible goals.
In the next section, we’ll look at the mucus layer that coats your gut from stem to stern. This mucus is shockingly important to your health, as you will see.
This article is adapted from the bestselling book I wrote with the top two scientists in the field: John F. Cryan and Ted Dinan. They are simply brilliant, and are changing the world one psyche at a time! From National Geographic.
Incredible read 👏🏼