Julianna Deardorff is leading a project to better understand how stress affects the biological and behavioral development of Latino youth in Salinas.
On a bright day in the first week of August, Julianna Deardorff escorted five Chilean scientists from Berkeley to The Farm, an agricultural center and farm in Salinas, California, about 100 miles south of the Bay Area. The Farm has been in the same family for four generations; the brothers who run it now have made strides in the past few decades to transition to organic farming. In the fields, the researchers found strawberries, one of 30 diverse crops grown in the sweeping fields. Others include corn, pumpkins, tomatoes—and, like most farms in the sprawling Salinas valley, lettuce.
The researchers were there to study growth—not of the verdant plants that thrive in the exceptional climate and nutrient- rich soil of the valley, but of the children who live in this agricultural community. Deardorff, an associate professor in the School of Public Health’s Maternal and Child Health program, wants to understand how early-life experiences can influence puberty and risky behaviors among adolescents. The bulk of her research focuses on how those pressures affect Latino populations. Recent research suggests that girls and boys of all ethnicities, and Latinas/Latinos in particular, are going through puberty at earlier and earlier ages around the world. Researchers often point to increasing rates of obesity to explain the trend, but Deardorff, like many other investigators, suspects that such an explanation is only part of the story.
In 2014 she launched a new research project, backed by a $2.5 million grant from the National Institute on Drug Abuse, to study how social adversity affects the biological development—including puberty—and risk-taking behavior of more than 600 Latino children who live in the farm-centered community of Salinas. Together with their parents, the youths have been participating in a longitudinal study called CHAMACOS that began before most of them were born.
Deardorff says the CHAMACOS population is particularly vulnerable: Latino adolescents are more likely to engage in unprotected sex and use substances at younger ages than their peers of other ethnic groups. In the United States, Latino adolescents have the highest rate of teen pregnancy among the major racial and ethnic groups. They’re also at risk for HIV/AIDS. According to the Centers for Disease Control and Prevention, Latinos accounted for more than 20 percent of new HIV cases in 2010, most of which occurred in people younger than 25. In the same year, the HIV infection rate for Latinos was more than triple the rate for whites. And that disparity, says Deardorff, represents a serious public health issue for the present and future generations of Latino youth.
The “kids” in Salinas
CHAMACOS stands for the Center for the Health Assessment of Mothers and Children of Salinas; in Mexican Spanish, the word chamacos means “kids.”
The study was the brainchild of Brenda Eskenazi, professor of epidemiology at the School of Public Health, who launched it in 1999 to better understand how environmental factors like chemicals—including the pesticides used to treat the fields where workers pick crops for eight to ten hours a day—affect the health of these children. Designed as a partnership between the families and the researchers, the study engaged participants from many different parts of the farming community, from growers to farmworkers.
Now, those children, many of whom have been studied since they were in utero, are becoming teens. They’re entering the age where they may or may not choose to engage in risky behaviors like sexual activity and substance abuse. And they’re doing it in Salinas, a town with high rates of teen violence.
“It was clear to me that a lot of the sexual risk behaviors we were seeing—and also some of the substance abuse problems, and engagement in unhealthy relationships and interpersonal violence—directly related to stressful life events these teens were experiencing.”
“We have a lot of youths in Salinas,” says Kimberly Parra, field office coordinator for the CHAMACOS study. She works firsthand with the study population, collecting data on body weight, blood pressure, and height; administering neurological assessments; and collecting samples of blood, hair and urine. “There’s a very young population in this area, young people with nothing to do, and they get curious or bored.”
That’s where Deardorff’s research interests enter the field, so to speak. She and her collaborators have been analyzing cardiac responses to stress, as well as levels of stress hormones (like cortisol), puberty hormones, and other chemicals in samples from the participants. They’re studying data on Tanner staging, a tool that gives researchers a way to assess physical development and pubertal progression, collected at early ages by Eskenazi and her team and continued into adolescence through Deardorff’s grant. In addition, Deardorff is incorporating information about cultural factors and pressures—from parents, families, social circles, and elsewhere—that can influence how and whether stress affects the youths.
Other research has failed to examine the many cultural and contextual strengths within Latino families and communities that can offset risk. Deardorff, however, wants to be able to see the whole picture of how stress unfolds in the lives of the teens. By pinpointing positive and negative effects on development, researchers might design strategies to lower the incidence of risky behavior.
“We’re interested in high-risk sexual behavior, and the interplay between that and substance use to predict HIV risk,” she says. “We’re also studying how puberty unfolds in this population, and how stress gets under the skin to accelerate pubertal development and lead to risky behaviors.”
Thanks to a $30,000 grant from UC Berkeley’s Center for Latin American Studies, Deardorff’s research has also bloomed into an international collaboration with those scientists she took tromping through the strawberry fields last August. She and Camila Corvalán, a physician and epidemiologist at the University of Chile’s Institute for Nutrition and Food Technology, in Santiago, were awarded the funds from Chile’s National Commission for Scientific and Technological Research to work together and share data. Corvalán is part of an interdisciplinary team studying nutrition in a large cohort of youths in urban Santiago. Though the two research populations are dramatically different—the Santiago youths are younger and live in the inner city; the Salinas chamacos are older and live in a farming community—both researchers say that combining their research could yield new insights into both cohorts. Corvalán and her colleagues visited Berkeley in August to compare notes and strategize their next steps.
Deardorff, a clinical psychologist who trained at Arizona State University in Tempe, says the Salinas project represents the convergence of two streams of research interests: One coming from clinical experience, and the other from her research.
Until 2012, she worked as the sole psychologist at the New Generation Health Center, a reproductive health center for teens run by UCSF. The center functioned like a community clinic in the heart of San Francisco. Time after time, she saw young people engaged in risky behavior; the majority of the girls she counseled were sexually active. Most of the youths who visited the clinic were Latina or African American. Many lived in unsafe neighborhoods where they witnessed violence, including gang activity, firsthand. Some came from immigrant families, where the children served as language interpreters for their families and witnessed discrimination against their parents.
“They had few role models who were doing what they wanted to accomplish, like going to college or waiting to have a family until after their education,” Deardorff says. All that turbulence took a toll on the young people who came into the clinic. “It was clear to me that a lot of the sexual risk behaviors we were seeing—and also some of the substance abuse problems, and engagement in unhealthy relationships and interpersonal violence—directly related to stressful life events these teens were experiencing,” she says of her experience at the UCSF clinic. “It was hard to disentangle where these behaviors started, and where to optimally intervene.”
On the research side, before she arrived in California, she’d been studying the negative effects that early puberty can have on a girl’s likelihood to engage in risky behavior. In a study published Dec. 1, 2005, in Pediatrics, for example, she and her coauthors studied the behavior of more than 600 girls aged 18-22 in Arizona and found that girls who went through puberty early were more likely than their peers to start drinking, and have sexual intercourse at an early age—which put them at higher risk for becoming teen moms. Their finding was in line with a growing body of evidence, from all over the world, that found the same connection. (More recent studies have found similar patterns in boys, linking early puberty to increased risk for substance abuse and, potentially, depression.)
Like many researchers, Deardorff suspected that the pressures that shaped these risky behaviors may have had even deeper roots. She joined a project, led by Lawrence Kushi at the Kaiser Permanente Northern California Division of Research, called the Cohort study of Young Girls’ Nutrition, Environment and Transitions, or CYGNET. The researchers focused on environmental factors that may spur early puberty but also studied social stresses that may play an important role. Deardorff led a 2010 study, published in the Journal of Adolescent Health, in which she and her CYGNET collaborators found that some girls were more likely to go through puberty early if they were raised without their biological fathers around.
That work, in accordance with other previous studies, suggested that negative early life events could have ramifications that influenced not only when a child went through puberty, but also the risk behaviors that followed.
“It felt like we were starting too late,” she says. “When we started to look upstream at factors influencing biological development, we found the same factors that were predicting risk behavior downstream.”
So, Deardorff headed upstream: She wanted to understand the impact of these early life stressors on the behavioral—and developmental—trajectories of children’s lives. She says she hadn’t spent much time researching the impact of the time between birth and five years old, much less stresses in utero.
The long-running CHAMACOS study gave her just such an opportunity. Eskenazi and her team had been collecting data on the 600 CHAMACOS participants for much of their lives, and Deardorff saw a way to extend that research in a new direction. But, she says, a project like hers would be impossible if she were going alone; to better understand the complex effects of stress requires investigators from a host of fields.
“It’s extremely important to recognize that none of this could happen if we weren’t working in a transdisciplinary manner,” she says. “We have psychologists, epidemiologists, nutritional experts, pediatric endocrinologists, neighborhood researchers, community members—without all of these experts, there’s no way to look at the complexity of human life over time.”
Salinas to Santiago
In 2013, Deadorff traveled to Washington, D.C., for an NIHsponsored international consortium on puberty research. She didn’t expect to return home with a new collaborator. But that’s just what happened: At the consortium, Deardorff met Corvalán from the University of Chile. Corvalán and her collaborators have been following a cohort of about 1200 children living in Santiago since 2006.
“Our main aim is to understand how early life nutrition can have an impact on obesity and obesity-related disease in the context of a country like Chile, a country that has rapidly moved from high rates of undernutrition to high rates of obesity,” says Corvalán. According to the World Health Organization, the last few decades have seen dramatic changes in the country. Between 1960 and 2000, rates of malnutrition among children younger than six dropped from 37 percent to 2.9 percent, but at the same time obesity became more prevalent. Now 20 percent of four-year-old children are obese.
The project began as a simple investigation, says Corvalán, but over time it grew. Researchers from different fields joined the study, asking new questions about pubertal development that widened the scope of the research. One of these collaborators, epidemiologist Karin Michels at the Harvard School of Public Health, invited Corvalán to the consortium where she met Deardorff. The idea of the consortium was for researchers to compare their findings on early puberty.
“I met with Julie in one of these meetings and started to talk to her about our girls,” recalls Corvalán. And something clicked: “We realized we had tons of similar questions” about the factors that influence early puberty that they wanted to answer through research. They began to suspect that by integrating findings from both cohorts they could shed some light on those questions.
“We were floored by the similarities in terms of our data collection,” recalls Deardorff. The researchers also realized that both of their respective cohorts were approaching the teen years, when risky behavior sets in.
The collaboration moved forward with Corvalán visiting Berkeley for a week with four other researchers from Chile. They included an epidemiologist, a dietician, and two psychology professors from Santiago’s Catholic University who were interested in Deardorff’s measurements related to parental relationships and risk behavior.
“We were very interested in seeing some of the tests being carried out in the cohort,” says Corvalán.
In addition to spending two days in Salinas, the researchers mapped out their strategies for data collection and sharing. They also visited the School of Public Health biorepository, where samples from CHAMACOS participants are included in the more than 150,000 stored biospecimens, which include blood, saliva, urine, teeth, and other tissues. Nina Holland, an adjunct professor in the School of Public Health’s Environmental Health Science Division, runs the facility.
Then, in December 2014, Deardorff and her team of researchers from Berkeley headed to Santiago, to visit Corvalán’s project. Team members included Eskenazi, Parra, and Kim Harley PhD ’04, MPH ’98. Asa Bradman PhD ’97 visited Chile in May 2015 to continue the conversation about environmental exposures and human development and health.
Life in the Salad Bowl
The Salinas Valley stretches about 90 miles from Castroville in the north to King City in the south, and beyond. Nestled between two mountain ranges—the Gabilan and the Santa Lucia—the valley is known above all else for agriculture. The exceptional weather and nutrient-rich soil, together with the waters of the Salinas river, combine to form an area where crops flourish. The valley grows more than 80 percent of the salad greens consumed in the United States, along with half of the cauliflower and mushrooms and a quarter of the celery. The growing season lasts eight to ten months of the year. Not surprisingly, the area is often called the “salad bowl” of the United States.
“We have psychologists, epidemiologists, nutritional experts, pediatric endocrinologists, neighborhood researchers, community members—without all of these experts, there’s no way to look at the complexity of human life over time.”
Fields of greens and vegetables stretch across the valley, from the base of the mountains to the city limits. The fields surround schools—the fences of which often carry signs warning of peligroso (dangerous) chemicals used in the fields. Growing, tending, picking and packing all those crops takes a lot of hands, which is why the area also attracts migrant farmworkers. In the 1930s, people fleeing the disastrous conditions of the Dust Bowl in the Midwest made their way to the valley and worked in the fields alongside Filipino workers. By the 1970s, many of the farmworkers had come from Mexico and Central America, and by the 1990s people of Mexican origin made up more than half of the population of Salinas, the largest city in the valley.
It’s a community where people know where their food comes from, says Parra, in the Salinas office of CHAMACOS. Like the investigators who are studying the effects of stress and other factors on behavioral and biological development, the residents of Salinas think often about growth—and family. Parra says she thinks Latino families have stuck with the CHAMACOS study over the years because it offers them some stability in their otherwise vulnerable, and potentially unstable, lives.
“They are invested in the project,” she says. “They come into our office and it’s like home. It’s one of the few places where they find consistency.”