Imagine if we had the ability to predict how teens’ health, social experiences, genetic makeup and living environment might influence their physical state later in adulthood. Now, dig further: What if we knew how it might influence their heath trajectory all the way into old age? How might that knowledge affect the ability of healthcare providers and policymakers to create a pathway to better health?
This vision drives the work of Kathleen Mullan Harris, James E. Haar Distinguished Professor of Sociology in the College of Arts and Sciences and a faculty fellow of the Carolina Population Center. She is the principal investigator and director of the nation’s longest-running study on the health of adolescents and their transition into early adulthood, spanning two decades.
Harris hopes that the U.S. National Longitudinal Study on Adolescent Health (or Add Health for short) will become the nation’s and perhaps the world’s most comprehensive study on aging. At UNC, co-investigators come from multiple disciplines across campus, including sociology, public health, biostatistics, cardiology, economics, epidemiology, genetics, nutrition and more.
The latest step toward making this vision a reality is a new $29 million, 5-year renewal grant from the National Institutes of Health (NIH).
An NIH review panel called the study a “national treasure” for the research community, citing it as “the only major study to trace the broad spectrum of health issues over the early life course, in combination with the evolving human capital, family and environmental situations of youth.”
Anatomy of Add Health
One of Add Health’s early goals was to understand the health and developmental trajectories of adolescents as they grow into adulthood.
This is the 20th year of the study, which has attracted more than $150 million in total funding to UNC.
The study originally surveyed a nationwide sample of 20,745 children in grades 7-12 during the 1994-1995 school year (when they were 12-19 years old). These children were then surveyed again in 1996. All racial and ethnic groups in the population of young people were represented in the sample. The study drew upon 132 public and private middle and high schools in 80 urban, suburban and rural communities across the nation.
It was unique because it collected multi-level and multi-generational health data from schools, classmates, peers, romantic partners, siblings and parents. Additional information about the communities and built environment where the adolescents lived was folded into the mix. (For example: city and county crime data, socioeconomic statistics, walkability of communities, the number of parks and green spaces, and the air quality.)
After the first two waves of data collection during adolescence, the National Institutes of Health, and the National Institute of Child Health and Human Development encouraged Harris to continue following the participants as they transitioned into early adulthood. Two more waves of surveys ensued in 2001-2002 (when respondents were 18-26 years old) and 2007-2008 (when respondents were 24-32 years old). The response rate at the last interview in young adulthood, 15 years after the adolescent interview, was more than 80 percent, which demonstrates a remarkable retention of the survey participants over time.
With the latest funding, a fifth wave of data collection is scheduled to take place in 2015 when the former adolescent cohort will be moving through their 30s.
Transition to adulthood: vulnerable period for health
Harris says Add Health has led her to value research integrated with other disciplines, with biomedical and public health perspectives. To add objective health measures to the vast social, behavioral, and environmental data, Harris collected physical samples that included blood, urine and saliva, which were then analyzed for cholesterol, glucose levels, C-reactive protein (a measure of inflammation), sexually transmitted diseases, hemoglobin A1C (a marker for diabetes), various markers of immune function (as indicators of chronic stress), as well as an array of genetic markers.
With the longitudinal life course data in Add Health, researchers have discovered that the transition from adolescence into early adulthood is a vulnerable period for health that sets trajectories into adulthood.
“These are young adults, so you think they should be healthy, but in the last wave we found 25 percent have hypertension and 6 percent have diabetes,” she said. “That’s a very high percentage among 24-32 year olds. We’re expecting to see an explosion of chronic illness earlier than normal in their life course.”
Harris said when adolescents move out of the house, they enter a high-risk time period for poor health and health behaviors. Although some of the health risks “straighten out” in later adulthood, results show increased use of tobacco products and alcohol in this life stage, along with an increase in the acquisition of sexually transmitted diseases, an increase in obesity, a lessening of physical activity and a loss of regular health care.
“But we also find that depression is less common and suicidal thoughts are lessened — so adolescents feel great, but they are not behaving in ways that help their health,” Harris says.
From adolescence to aging
Harris plans to continue shaping Add Health into a multigenerational study of the parents of the original participants, the participants themselves and the 15,000 children the participants have given birth to since they filled out their first Add Health questionnaire in 1994. By collecting genetic samples from all involved, Harris envisions researchers performing genetic mapping between generations as well as studying how social influences and the built environment have affected people’s health across their lives.
“Most aging studies start at age 50,” she points out. “The National Institute of Aging knows that is too late because the aging process starts much earlier. So they are eager to get their hands on Add Health because they know they have so much to learn about aging from our data.”
So far the data gleaned from Add Health have spawned 20 books and 75 book chapters, more than 500 theses and dissertations, and nearly 2,000 peer-reviewed articles published in more than 350 different academic journals.
Researchers have delved into topics as diverse as what causes health disparities, the causes and consequences of obesity, gene-environment interactions, substance use and abuse, and social stratification processes, to name only a few.
Harris says she wants the biggest take-home message from Add Health to be this: “Don’t overlook adolescence, it’s very important — especially in terms of the effects of the social environment.”
Looking ahead to the next wave of data collection, and to the expected findings of declining health, Harris offers a glimmer of hope:
“Add Health offers one of the best opportunities for understanding pre-disease pathways,” she says. “Maybe there are environmental or behavioral precursors to disease that can be identified so that we can develop interventions earlier in adolescents’ lives.”
- Add Health is the nation’s longest running study on adolescent and adult health, 20 years and counting.
- Add Health data has been shared with more than 10,000 researchers around the world.
- The 20,000 children who originally participated in Add Health have now moved into adulthood and have about 15,000 children of their own.
- Findings from the study provide insight on obesity, hypertension and heart disease, diabetes, chronic stress, teen pregnancy, STDs, alcohol and substance use and abuse, depression, suicidal thoughts, and the effect of social environments upon choices and health outcomes, among other things.
- Learn more at www.cpc.unc.edu/projects/addhealth.
[ By T. DeLene Beeland ]