Connecting Poverty and DNA
WHY YOU SHOULD CARE
Because if negative experiences can change our biology, we need to start changing the experiences.
Our socioeconomic class largely determines our health. Poverty boosts the risk of heart disease, obesity, depression and a host of other conditions. But how? It doesn’t just limit our access to health care. Some scientists believe poverty gets deep under our skin — and even changes how our genes behave.
The poor are more stressed, eat less healthy food and live in more polluted neighborhoods compared with wealthier individuals. Some researchers think that exposure to these and other environmental stressors in childhood, and even in the womb, can leave lifelong molecular markings on our genes that change their activity in ways that contribute to disease. Traumatic experiences can “switch off” genes that are crucial for responding to stress, making kids more likely to suffer depression later on, while air pollution can turn off genes that regulate the immune response, thereby increasing the risk of asthma, for example. These markings may even be passed down to future generations. The good news, though, is that we may be able to “delete” them with medical treatment and policies that reduce socioeconomic disparities.
Scientists believe poverty gets deep under our skin — and even changes how our genes behave.
These molecular markings — so-called epigenetic changes — alter how genes behave without rewriting the information they encode in the structure of DNA. Epigenetic changes are like tagging genes with chemical Post-it notes that tell a cell to switch a gene on or off. Tagging a gene with a chemical group called an acetyl group switches it on, while tagging it with a methyl group switches it off.
“Epigenetics is a really big advance in looking at mechanisms for how biology can be changed in response to our experiences,” said Audrey Tyrka, an associate professor of psychiatry and human behavior at Brown University. “It happens in part through epigenetic changes that influence whether certain genes are expressed or not.”
Children are especially vulnerable to epigenetic changes. Last year, a University of British Columbia study found that adults who were poor as children showed epigenetic modifications that were linked with stronger immune responses, which could affect their ability to respond to illness. Strikingly, the researchers didn’t see these patterns in people who had experienced poverty only as adults. Michael Kobor, a medical geneticist who led the study, suspects that there is “a critical window in early life” when people are most susceptible to poverty’s influence on health.
Poverty also makes children more likely to suffer molecular scars that could affect their mental health. Abuse and other types of trauma may be partly to blame — in the U.S., low-income kids are 22 times more likely to suffer abuse and neglect than their more affluent peers. Last February, Tyrka and other scientists reported that adults who had experienced abuse and other types of trauma during childhood showed increased methylation, or lowered expression, of a gene that encodes a protein crucial for mediating the stress response, indicating an impaired ability to cope with stressful situations and a higher risk of depression and other mood disorders.
The high levels of pollution, pesticides and other toxins found in underserved areas can also leave lasting imprints on children’s DNA. Stanford and UC-Berkeley scientists reported last October that air pollution and secondhand smoke can lead to increased methylation in two immune genes in kids living in Fresno, a poor community in central California. These genes tighten the reins on the immune system to prevent it from reacting to noninfectious agents. When they can’t do that job effectively, asthma sets in.
A recent Northwestern University study found that mothers with high BMI levels gave birth to children with epigenetic changes to genes that are crucial to the development of cancer and cardiovascular disease.
Expectant mothers may even pass these asthma-inducing changes to their children. In August 2012, University of Ohio researchers reported that pregnant women who lived in high-traffic areas in Manhattan and the South Bronx gave birth to infants with increased methylation of one of the two immune genes examined in the Fresno study.
A poor diet can also leave its mark on developing babies’ DNA. In 2010, researchers from Baylor University and other institutions reported higher levels of methylation in five genes in Gambian children conceived during the peak of the rainy season , when food is less available. The silencing of one gene is associated with Tourette syndrome, while another is linked to hyperthyroidism.
But in some disadvantaged communities, the problem isn’t a lack of food so much as limited access to healthy food. In the U.S., for example, lower-income neighborhoods tend to have higher obesity rates — which might also have epigenetic consequences. A recent Northwestern University study, for example, found that mothers with high BMI levels gave birth to children with epigenetic changes to genes that are crucial to the development of cancer and cardiovascular disease.
If pregnant rats are exposed to nicotine, not only will their offspring develop asthma — so will their grand-offspring, even if they were never exposed to nicotine.
Epigenetic changes may even transcend multiple generations, according to preliminary research on smoking, which is also more prevalent among the poor . UCLA scientists found that if pregnant rats are exposed to nicotine, not only will their offspring develop asthma — so will their grand-offspring , even if they were never exposed to nicotine. The team saw epigenetic changes in the first set of offspring’s lungs, ovaries and testes, suggesting a mechanism for how asthma was passed on to the grand-offspring. The findings are consistent with the Children’s Health Study from Southern California, which reported that individuals whose maternal grandmother smoked had a higher risk of asthma regardless of whether their mother smoked.
DNA isn’t necessarily destiny, though. Unlike genetic mutations, epigenetic changes are reversible. Medications can remove these modifications, just like many cancer drugs already do. Eventually researchers hope to identify an “epigenetic signature” of poverty. This way, clinicians can target individuals whose DNA displays this signature so they can detect and treat diseases early. But “a more efficient way to do it is to reduce social inequity in first place,” said Monica Uddin, an assistant professor at the Wayne State School of Medicine in Michigan.
Tyrka agreed. “We have to overhaul our understanding of what it means to provide healthy environments to prevent development of disease,” she said.
Even if the findings do prove compelling, some experts are doubtful whether they’ll convince policymakers to enact reforms.
But more research is needed before epigenetics even registers on policymakers’ radars. So far, most epigenetic studies have been done on rodents. Scientists need to conduct many more human studies, especially long-term analyses to prove that epigenetic markings are heritable. They also need to do more studies like Kobor’s that look directly at the association between socioeconomic status and epigenetic changes.
Even if the findings do prove compelling, some experts are doubtful whether they’ll convince policymakers to enact reforms. “The intergenerational effect might have some bearing,” said Mark Rothstein, Herbert F. Boehl Chair of Law and Medicine at the University of Louisville School of Law. “But we’ve been thinking of environmental justice for a long time, that some people ought not to bear the risks of exposure, and that’s not had any effect.”
Still, some scientists remain hopeful. Tyrka believes raising public awareness is an important first step. “When the public understands that experiences can change your biology … they’re going to want to get rid of these stressors so all infants and people have a chance at a healthy life,” she said. “The more we understand, the more it’s really incumbent upon us to eliminate the socioeconomic disparities we see so strongly.”