Genes! They’re responsible for all sorts of things.
Like the color of your eyes, your likelihood to bald, and even your risk of developing certain diseases.
Through the study of the genome, which is an organism's complete set of DNA containing all genetic information, we know things like someone with the BRCA gene mutation is at higher risk of developing breast cancer, or someone with the APOE e4 allele is more likely to develop Alzheimer’s.
In the 90s, the race to map the human genome was thought to be the solution to all our disease problems—if we could pinpoint which genes caused which diseases, we could also pinpoint treatments tailored to the individual.
It was a huge accomplishment that taught us two very important things:
Maybe we shouldn’t be looking at single points (or in this case genes) as the origin of disease, but rather that complex systems interact with each other to influence outcomes.
Sometimes, genes can go awry through no fault of your ancestors when the environment you live in influences how they are expressed.
These influences are known as the “exposome.” In the same way the genome is concerned with all your genes, the exposome is concerned with all your exposures.
The term was created in 2005 by Dr. Chris Wild and encompasses every exposure an individual is subjected to from conception until death.
As we move away from the idea that individual, inherited genes are the main source of illness, the study of the exposome and all its complex interactions is moving to the forefront of science.
And the interactions are incredibly complex, because they include the ways that very different things influence each other.
Environmental factors like air, water and food. Social factors like racism and poverty. Behavioral factors like smoking or exercise. Or external sources of disease like viruses, bacteria and other pathogens.
An example of multiple exposomic factors contributing to a genetic change could be something like the constant stress due to discrimination increasing cortisol levels in the brain which triggers the expression of genes that can result in cognitive decline.
All day, every day your cells are taking the instructions embedded in your RNA and using those instructions to build and express proteins, and sometimes those instructions are getting corrupted by external forces that have made their way into your body.
Take, for example, air pollution.
Obviously, we all know that air pollution is bad for you. We’ve known it since the Victorian age when the theory of miasma, or bad air, was the commonly cited explanation for illness.
It was the idea that “dirty air” caused all variety of malady.
While miasma theory was on the right track but for the wrong reasons, we’re starting to understand more and more that the invisible particles in bad air can change the way our cells work and have a long-lasting impact on health.
One study found that girls who were regularly exposed to fine particulate matter (microscopic particles in the air smaller than 2.5 micrometers in diameter) consistently got their periods earlier.
Which might not seem like a huge deal until you realize that earlier period onset is associated with an increased risk of certain cancers and heart disease later in life.
Onset of menstruation in people under 12 years old is also associated with a decrease in fertility compared to people who got their period between the ages of 12 and 13.
While there are likely a variety of complex reasons that exposure to fine particulate matter can trigger early puberty, one theory is that these particles act as what’s known as “endocrine disruptors.” This means they can interact with certain hormone receptors in the body, potentially triggering the onset of puberty.
It’s not just hormones that can be impacted by these microscopic bits.
Research has also demonstrated an association between exposure to particulate matter from traffic pollution and developing signs of Alzheimer’s disease in the brain.
These studies appear to show that prolonged exposure to traffic pollution can trigger the production of plaques in the brain, a sign of Alzheimer's disease, particularly in people who lack the genetic factors we already recognize as being a risk for disease development.
This indicates that it is, indeed, the pollution that causes plaque and not genetics.
Research has also found an association between fine particulate matter exposure (particularly in the third trimester or early childhood) and developing autism.
Another example of the air we breathe impacting our health comes in the form of lung cancer.
Rates of lung cancer in people who have never smoked are increasing, at least partially as a result of exposure to radon: A colorless, odorless gas that comes from soil and sometimes water.
One study found that gene mutations in non-smokers were more prevalent in areas with high radon exposure.
And the way America likes to design new construction, with high ceilings and greater square footage, could be contributing to radon exposure when the homes are built to be energy efficient and trap the gas inside.
Research has also shown that people exposed to wildfire smoke within the year after having lung cancer surgery have significantly lower survival rates.
Urban wildfires, like the ones experienced in Los Angeles this winter, are reviving old health issues in a new way.
According to the CDC’s Morbidity and Mortality Weekly Report, concentrations of lead in the atmosphere in LA saw a 110-times increase during the fires, due to the large proportion of buildings which contained lead paint being burnt.
Although the amount of lead in the air returned to pre-fire levels quickly, it’s unclear the lasting impact this could have as the lead settles on the ground and in water sources.
Here in Atlanta, there was recently a fire at a factory which produced and stored chemicals for pool and spa maintenance. The burning building released huge plumes of chlorine-scented vapor that were carried on the wind throughout the metro area.
Rockdale county residents near the site were put under shelter in place orders for weeks due to poor air quality.
A huge issue when it comes to the exposome is the way we regulate, or rather don’t regulate, a lot of new chemical exposures.
Unlike with medications that go through the clinical trial process to be evaluated for safety, many of our industrial chemicals only get removed from use once they’ve been shown to be a threat to health, rather than having to prove they are safe before they can be put into use.
But because there are so many kinds of industrial chemicals we are exposed to (be it waterproofing materials, detergents, solvents, non-stick cookware, flame retardants, and the whole host of chemicals we get exposed to as a byproduct of production), teasing out which exposures result in harm becomes even more complicated.
And in the rare cases when a compound is identified as harmful, it’s often simply replaced with a different, but not necessarily different enough compound, and the process to see the impact it has begins again.
The exposome is more than just the physical elements people are exposed to. It’s also the external factors which can increase your likelihood of exposure.
Nearly everyone has some level of risk of coming into contact with chemicals that can influence our body’s systems to create disease, but the threat is particularly high for people of a lower socioeconomic status.
Concentrations of fine particulate matter increase closer to roadways, which might put you on edge during your work commute but is particularly concerning for low income neighborhoods that tend to be clustered around freeways, and often tend to be made up of people of color.
Right here in Atlanta, interstate 20 was intentionally built to separate white neighborhoods from black, and the proposed interstate 485, which would have been an additional north/south route to alleviate traffic on I-85, was never built because it would have cut directly through the predominantly white and wealthy neighborhoods like Virginia Highlands and Morningside.
Richer communities also have lower tolerances for the concept of chemical belching factories being in their backyards, and, more importantly, have the political will and know-how to stop them.
Poorer communities don’t just miss out on the appealing property values that come with the tree-lined streets and public parks that “nice” neighborhoods have: those green spaces help mitigate and filter air pollution and decrease urban temperatures.
The exposome is made up of so many factors, both very large (like structural racism) and very small (like the chemicals, within the microplastics, inside our guts), and that can make the task of measuring the external factors that put us at risk of disease seem quite overwhelming.
