Epigenetics: The Controversial Science Behind Racial and Ethnic Health Disparities

Why what we eat, are exposed to, and experience today may shape the health of our descendants tomorrow.

When patients hoping to conceive a happy and healthy child visit an expert in Ayurveda — a form of alternative medicine that originated in India several thousand years ago — they are sometimes told to follow a surprising set of orders. If either the man or woman feels thirsty, hungry, sad, angry, or afraid, the couple is told, they should forgo any potential baby-making activity. Only when happy, satiated, and feeling connected to one another should they bathe, dress in fresh white clothing, apply particular oils to their bodies — and then proceed.

To most people with a passing understanding of DNA and heredity, all that prep work may sound utterly absurd. But a fast-growing field of science, known as epigenetics, strongly suggests that what we experience, consume, and encounter from the moment we are conceived matters. Epigeneticists study molecular changes including DNA methylation, the technical term for the way that our environments and experiences can subtly alter our gene activity. The genes turned "on" and turned "off" when we are exposed to certain chemicals, man-made poisons, or — perhaps most surprisingly — emotional experiences, can make us more or less susceptible to particular health problems.

"There are conditions and serious diseases occurring in the population today at a rate that simply cannot be explained by the rules of mammalian genetics alone," says Michael K. Skinner, a professor at Washington State University and the founding director of the Center for Reproductive Biology in the School of Biological Sciences.

In other words, the rate at which children in some demographic groups are born too soon, the fact that entire geographic regions suffer from elevated rates of obesity and diabetes, and even the frequency with which American children today are diagnosed with autism cannot be sufficiently explained by the Punnett Squares every high school biology student must master, Skinner says.

"Genetics is part of the story, an important part of the human story," says Skinner. "But epigenetics, that is the other half of the equation."

The Effects of Chronic Stress

An Emory University study released last year suggested just how large epigenetics may loom in one of the country's most egregious racial and ethnic health disparities — premature births. The United States' premature birth problem is the worst in the industrialized world, especially for racial and ethnic minorities. About 10.5 percent of white children were born before 37 weeks gestation in 2012, along with 10.3 percent of Asian babies. But about 11.7 percent of Latino children, 13.6 percent of Native American babies, and 16.8 percent of black infants arrived too soon.

Elizabeth Corwin, dean of research at Emory University's Woodruff School of Nursing, and a team of researchers closely tracked more than 100 women during the last three months of their pregnancies. They found that women of all races and ethnicities who were poor during their pregnancies were more likely to suffer from chronic stress, a biologically detectable and quantifiable condition. The same was also true, says Corwin, of middle-class black women, and all Latinas except for those who were immigrants. In fact, the problem was particularly pronounced in those last two groups.

Black women and Latinas across socioeconomic categories — those with and without insurance, college degrees, and access to the best food and information — were significantly more likely to test positive for elevated levels of stress hormones and conditions that those hormones can set in motion. This made the women more likely to deliver their children early. Chronic stress, the team determined, is the reason approximately 30,000 more African-American babies are born prematurely each year than any other group.

"We all experience stress," Corwin says. "Some weeks, who doesn't feel utterly overwhelmed? But what we found was that chronic stress is something entirely different. It [is] created by some combination of finances, relationships, community, and experiences like racism — actual and perceived."

Corwin knows results like this are not easy for everyone to digest or accept. She's seen the comments beneath online stories about her research, reflecting what can sometimes only charitably be described as of the "Oh, come on, that's another excuse," variety. But studies confirming the negative effects that chronic stress can have on pregnancy, infant, child and even adult health are, in her words, "voluminous, solid, and long known."

Across the country, Skinner's work at Washington State University has gone a step further. Skinner and his team have proven exposure to certain chemicals can affect the genes likely to activate in the sperm and egg cells of mice four generations down the line. His findings have been repeated in other large animals, been published in peer-reviewed scientific journals, and have significant implications for humans.

In 2013, Skinner and his team published research showing that direct exposure to DDT left mice with a slightly elevated rate of certain diseases. But by the time those mice had grandchildren, more than 50 percent of the male mice developed obesity. In fact, Skinner's research found that DDT left 90 percent of the progeny of the mice originally exposed more likely to develop obesity, experience lower sperm counts, or contract other even more serious health conditions. This pattern continued through four generations, to the great-grandchildren of the mice originally exposed to DDT.

In the U.S., farmers used DDT widely after World War II to prevent insects from attacking crops, and local and state governments used it to drive down the number of disease-carrying mosquitoes. The substance was banned in the United States in the early 1970s. But three generations after DDT exposure became common, Skinner says, the country saw major increases in human obesity.

Race, Class, and Health

Despite these studies, it's hard to imagine policymakers hearing about Corwin's research and deciding the nation must try to reduce minority poverty rates or confront institutional racism to deal with the problem of premature births. Certainly, members of Congress who still doubt the existence of climate change might balk at Skinner's revelations — that the chemicals and everyday substances used or emitted in our homes, offices, and cars can cause disease-promoting genes to activate in the human body for generations.

Even so, the potential race and class implications of these findings are troubling. Four to five generations ago, the ancestors of today's middle-class African-Americans were likely to be enslaved in brutal physical and emotional conditions. Large numbers of Mexican nationals came to the U.S. beginning in the 1940s to work in the agricultural industry and were regularly exposed to chemicals used in farming. Some workers were even sprayed with pesticides upon arrival. Today, Mexican-Americans make up the largest portion of the nation's fast-growing Latino population. On top of that history, informal social codes, land prices, and land-use laws often leave poor communities closest to local waste facilities, mines where workers rake coal from the earth, or coastlines dotted with refineries.

Still some epigeneticists remain optimistic that the science and the public policies that should flow from it will prevail. The epigenetic changes that science has uncovered aren't as dramatic as humans becoming, say, a species that glows in the dark, says Carmen Marsit, an associate professor of pharmacology and toxicology at Dartmouth University. But they are changes that can shape human health.

"People, particularly in America, may believe that famine exposure during pregnancy could do something harmful," Marsit says. "But it is also possible that chronic stress or chemical exposure can also lead to effects, and that similar molecular mechanisms are at play. There's really a lot of amazing research out there proving that."

Marsit is also the codirector of the program in cancer epidemiology at the Norris Cotton Cancer Center. His own research is focused on determining whether chronic low-level exposure to substances such as arsenic — something common to well water frequently consumed in New Hampshire — can create neurobehavioral deficits and even cardiovascular problems.

Some government officials do embrace the idea that our social experiences and substances to which we are exposed may be making us more susceptible to certain health problems. Ana Penman-Aguilar is the associate director for science in the Office of Minority Health and Health Equity at the Centers for Disease Control and Prevention. CDC is what Penman-Aguilar describes as "very passionate" about the fact that the health of the nation as a whole cannot be improved without making significant gains in minority health. To do so, CDC has increasingly focused on projects that identify and address the social determinants of disease, she says.

"We know that no matter what we do, the genetic research — and it is important research — is going to continue," says Penman-Aguilar. "So, we ensure that there is also a focus on the social determinants of disease, the way income, diet, neighborhood — basically how and where we all live, learn, work, and play — can drive health disparities."