An 18-year study of about 2,000 children aged 5-18, conducted in part by researchers at Duke University and published in June, found that children who grew up in neighborhoods marked by economic deprivation, physical dilapidation, and social disconnection experienced negative effects at a cellular level—specifically, in epigenetic changes, aka changes in how your DNA code is expressed in the body.
“Children raised in more socioeconomically disadvantaged neighborhoods appeared to enter young adulthood epigenetically distinct from their less disadvantaged peers," the study reads. "This finding suggests that epigenetic regulation may be a mechanism by which the childhood neighborhood environment alters adult health.” In non-science speak, this means growing up in a socioeconomically disadvantaged environment can impact the functioning of your genes—and therefore your health—into adulthood.
This isn't the first study showing how one’s environment can impact their genes. A whole field of science, epigenetics, focuses on how one's environment influences the genome (the genetic material of an organism). But this latest study shows that disparities between different socioeconomic groups can impact a person's well-being down to the cellular level—more evidence that the social determinants of health deserve more attention and solutions.
Here, Aaron Reuben, one of the study's co-authors, and epigenetics expert Kenneth Pelletier, MD, PhD, the author of Change Your Genes, Change Your Life, explain more about how one’s childhood environment affects their genes, and just how big that impact is.
How environment impacts genes
Before we get into the nitty-gritty of which environmental factors impact genes, it's helpful to have a baseline understanding of epigenetics. Dr. Pelletier explains that 5 percent of an adult’s genes are unchangeable. The other 95 percent are malleable, and epigenetics focuses on what alters those genes (for better or for worse) and how long those effects last.
Reuben explains that everyone is born with a DNA structure that's set. But this DNA doesn’t operate in a vacuum; it gets instructions from chemical compounds and proteins in our bodies. And changes in our environment can alter the instructions our DNA gets (kind of like turning a light switch on or off), leaving behind a mark on the gene. The changed instructions can cause other changes within our bodies, and even be passed down to our offspring.
"The gene is embedded into every cell, and the cells are integrated into the human body, and the human body is integrated into its environment," Dr. Pelletier adds. "Any number of things that happen in the environment have both direct and indirect impacts on the genes." For example, if you breathe in a toxic chemical, that might turn on a destructive expression of particular genes. "Biochemicals can cause the gene to be excessively present or it could cause the gene expressions to not be active enough," he says.
Dr. Pelletier says that the effects of this can be truly profound. For example, he says that chronic inflammation is the root cause of many health conditions such as heart disease, cancer, arthritis, and gastrointestinal problems. Someone may have a genetic predisposition for one of these health conditions, but if they aren't exposed to inflammatory conditions (also connected to lifestyle habits such as diet) they may never manifest. But being in an environment that causes inflammation could "turn on" the genetic markers for these conditions, causing them to appear.
The environmental factors that affect genes the most
Epigenetic researchers like Dr. Pelletier and Reuben study what environmental factors can lead to gene-altering inflammatory responses and some studies over the years have highlighted some significant connections.
Both experts say that there is a large body of evidence showing that air pollution could have negative effects on a genetic level. "There are a number of human studies showing that a gene called CYP1b1 is involved in the metabolism of hydrocarbons," Reuben says. "Cigarette smoke, car exhaust, and solar emissions from power-generating facilities and waste-burning facilities all generate hydrocarbons." These specific sources of hydrocarbons (compounds of hydrogen and carbon found in substances like coal and natural gas) have been shown to mutate the CYB1b1 gene, he says, which is a reason why they're known toxins. To his point, a study published in the journal Clinical Epigenetics found that DNA changes associated with air pollution were connected with “long-term negative respiratory health outcomes, including the development of lung diseases.”
Reuben's study of children showed that CYB1b1 gene mutations are more likely to affect those living in low-income urban areas, because they are more likely to be exposed to these specific types of toxins. "It's an interesting finding that we didn't set out looking for, but [it] came up," he says. "This isn't something [doctors] really think about with folks that young, but we're seeing that at a young age, already, this exposure [to hydrocarbons] is creating differences at cellular levels which can wire them for these [negative] outcomes later on," Reuben says.
Another major environmental stressor could be noise pollution, aka unwanted and disturbing sounds such as honking cars, construction, and sirens—a subject that Reuben is currently investigating. One 2017 study (on rats), published in the journal Environmental Research, found that noise pollution alters DNA methylation patterns, which control what genes are expressed. Reuben says this is likely because noise pollution can be a source of inflammation: It can make you feel stressed, activating stress-related hormones in the body, leading to (drumroll) inflammation—which can change how genes are expressed.
This mechanism is true for all sources of chronic stress. Stress, Dr. Pelletier says, "changes the biochemistry of cells from one that is inherently regenerative to one that's destructive." This destructive turn is called catabolism. "It's when a cell burns the components utilized to create energy," Dr. Pelletier says. This can lead to health problems including heart disease, gastrointestinal problems, and cancer. As Dr. Pelletier says, chronic stress creates chronic inflammation. One paper published in the journal Nature Clinical Practice Oncology that took into account 165 scientific studies found that stress-related psychosocial factors are associated with higher cancer incidence in initially healthy populations.
"If a child is experiencing traumatic events such as having a difficult home life or being bullied at school, that would show up in their inflammatory levels, if you were to test them," Dr. Pelletier says. "This shows the negative impact stress can have on genetic expression."
Another factor Dr. Pelletier says has a massive effect on genes is nutrition. This one is a double whammy: Getting insufficient nutrients in childhood affects brain development and growth as well as genetic expression. "Especially for the first eight years of life, there are certain critical developmental periods where the brain matures in a certain chronological sequence," Dr. Pelletier says. "If that sequence is disrupted, meaning if a person is deprived, that can lead to permanent cognitive impairment." Research has also shown that malnutrition can alter DNA, putting someone more at risk for conditions such as cardiovascular disease, diabetes, or decreased cognitive function later in life. All of this indicates that if a child grows up in an area where there is limited access to healthy food, their health may be affected as an adult.
While the connection between environment and gene impact is clear, Reuben says that what's less clear is just how long their effects last or how reversible they are. "We're really just at the beginning of understanding epigenetics and more research definitely needs to be done," he says.
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