Are Stressful Developmental Processes of Youths Leading to Health Problems Amplified by Genetic...
Transcript of Are Stressful Developmental Processes of Youths Leading to Health Problems Amplified by Genetic...
EMPIRICAL RESEARCH
Are Stressful Developmental Processes of Youths Leadingto Health Problems Amplified by Genetic Polymorphisms? TheCase of Body Mass Index
Kandauda (K.A.S.) Wickrama • Catherine Walker O’Neal •
Assaf Oshri
Received: 11 December 2013 / Accepted: 27 February 2014 / Published online: 8 March 2014
� Springer Science+Business Media New York 2014
Abstract Although previous research has documented
the adverse influence of early socioeconomic disadvantage
on youths’ physical health outcomes and the increase in
health inequalities over the early life course, little is known
about genetically informed sequential life course devel-
opmental processes leading to health outcomes. Consistent
with the life course-stress process perspective, we
hypothesized that early socioeconomic adversity initiates a
stress process over the early life course. This process
involves the disrupted transition from adolescence to
young adulthood, which increases the risk of health prob-
lems during young adulthood. Behavioral, psychosocial,
and genetic data were collected from 12,424 adolescents
(53 % female) over a period of 13 years participating in the
nationally representative National Longitudinal Study of
Adolescent Health (Add Health). Early cumulative socio-
economic adversity and the polygenic influence were
measured using composite indices. The study provided
evidence for stressful developmental processes of adoles-
cents, involving parental rejection, depressive symptoms,
and adolescents’ precocious transition. This longitudinal
process was initiated by early cumulative socioeconomic
adversity and eventuated with young adults’ increased
body mass index (BMI). Furthermore, the study provided
evidence for the influence of life context–gene interactions
(G 9 E) on adolescents’ precocious development and
young adult BMI (after controlling for the lagged measure)
amplifying the stress process over the early life course.
These findings emphasize the need for incorporating indi-
vidual genetic characteristics in a longitudinal context into
life course stress research. Furthermore, policies focused
on eradicating childhood/adolescent adversities are neces-
sary as well as youth programs and policies that promote
youth competencies that aid in their successful transition to
young adulthood.
Keywords Early life adversity � Genes � Obesity
Introduction
Early socioeconomic adversity during childhood and early
adolescence (hereafter, referred to as early adversity) is
linked to stressful developmental processes leading to
health problems in adulthood (O’Rand and Hamil-Luker
2005; Wickrama and O’Neal 2013). Some youths are
capable of avoiding the damaging influence of early
adversities, while others may experience detrimental
developmental processes involving a sequence of age-
graded stressful life experiences and negative outcomes
(Oshri et al. 2013; Wheaton and Gotlib 1997; Wickrama
et al. 2008). These prolonged stress effects are consistent
with the life course-stress process perspective (Pearlin et al.
2005). In the present study, we hypothesize that early
socioeconomic conditions and parental rejection/
K. Wickrama
Department of Human Development and Family Science, 103
Family Science Center I, University of Georgia, Athens, GA,
USA
e-mail: [email protected]
C. W. O’Neal (&)
Department of Human Development and Family Science, 261
Dawson Hall, University of Georgia, Athens, GA, USA
e-mail: [email protected]
A. Oshri
Department of Human Development and Family Science, 208
Family Science Center I, University of Georgia, Athens, GA,
USA
e-mail: [email protected]
123
J Youth Adolescence (2014) 43:1096–1109
DOI 10.1007/s10964-014-0109-8
negligence (hereafter, parental rejection) set a process in
motion that disrupts the successful transition of adolescents
to adulthood by accelerating the acquisition of adult roles
(i.e., precocious development), such as parenthood, mar-
riage or cohabitation, truncated education, and independent
living. These precocious transitional events create a
stressful life context, which increases adolescents’ risk of
declining physical health during the transition to adulthood
(Foster et al. 2008; Wickrama et al. 2008). However, less is
known empirically about the longitudinal processes that
lead to these unfavorable health risks as research taking a
‘‘long-view’’ to examine an extended period of the early
life course is less common.
Obesity and being overweight are major public health
problem in the United States (Finucane et al. 2011).
Approximately 30 % of adolescents and 69 % of adults in
the United States are overweight or obese (Centers for
Disease Control and Prevention 2012). Obesity has been
shown to be associated with both contemporaneous and
long-term physical health (e.g., heart disease, diabetes,
certain cancers, and orthopedic and endocrine problems)
and mental health problems (e.g., depression) (WHO
2002). Recent research has also linked obesity to other
dimensions of wellbeing, such as the quality of romantic
relationship, socioeconomic attainment, and social func-
tioning (Crosnoe 2007; Merten et al. 2008). Obesity,
especially when experienced early in the life course, is
strongly associated with negative consequences in adult-
hood (Ferraro and Kelley-Moore 2003).
We hypothesize that variations in multiple candidate
genes involved in regulating the serotonergic and dopa-
minergic neurotransmitter systems accelerate (or impede)
stressful developmental processes by influencing age-gra-
ded developmental outcomes directly (G) and interactively
with the life contexts (G 9 E; Belsky and Beaver 2011;
Wickrama et al. 2013a, b; Wickrama and O’Neal 2013).
Researchers suggest that the impact of context–gene
interplay on an individual’s behavior (i.e., phenotypes)
may not appear until later in life because environment
salience and susceptibility may increase from childhood to
young adulthood (Shanahan and Boardman 2009). Fur-
thermore, recent studies have shown that multiple genes
may cumulatively influence developmental outcomes of
youth (i.e., a polygenic effect) (Belsky and Beaver 2011;
Simons et al. 2012; Wickrama et al. 2013a, b; Wickrama
and O’Neal 2013). To our knowledge, no previous study
has examined cumulative genetic influences on develop-
mental processes over the early life course leading to adult
health outcomes.
The current study investigates body mass index (BMI)
as a marker of poor health in young adults. As depicted in
Fig. 1, the present study will examine if early adversities
are associated with developmental processes implicated in
young adults’ BMI. The present study will also examine if
these adverse processes are strengthened through additive
genetic influences on age-graded developmental outcomes
(G) and amplified (or impeded) by genetic polymorphisms
through interactions with age-graded social contexts
(G 9 E).
We expect that early cumulative socioeconomic adver-
sity will be associated with parents’ rejection of their
children (Path A). In turn, parental rejection will increase
the likelihood of adolescents’ depressive symptoms (Path
B), which has implications for their precocious acquisition
of adult roles (Path C). Consistent with the life course
perspective, we expect that adolescents experiencing a
precocious transition will encounter adverse health conse-
quences, in particular the development of higher levels of
BMI (obesity) in young adulthood, because it creates a
chronically stressful life context for emerging adults (Path
D). Paths A, B, C, and D will form a stressful develop-
mental pathway through adolescence, emerging adulthood,
and young adulthood indicating a ‘‘chain of risks’’ begin-
ning with early adversity and resulting in sequential neg-
ative developmental outcomes.
Stressful Developmental Processes
Research has shown that the health risk of cumulative
socioeconomic adversity is considerably stronger than the
independent effect of individual dimensions of socioeco-
nomic adversity (Bauman et al. 2006). Consistent with the
family stress model, we hypothesize that cumulative
socioeconomic adversity increases emotional problems of
parents because they are more likely to experience multiple
stressful circumstances, including family economic pres-
sure, adverse work conditions, lack of social support,
community stress, and marital problems. Distressed par-
ents, in turn, are more irritable, authoritarian, rejecting,
neglecting, and hostile toward their children (Conger et al.
2010). Furthermore, parents with a lack of resources and
income may not find adequate time to spend with their
children, contributing to parent–child distancing and child
negligence. Thus, in the present investigation, we will
investigate the influence of early cumulative socioeco-
nomic adversity by generating a composite index of dif-
ferent dimensions of adversity.
Parental rejection is implicated in adolescents’ feelings
of worthlessness, unhappiness, and their pessimistic out-
look on the future (Benoit et al. 2013). For example, early
adverse socioeconomic characteristics, such as family
economic hardship, low parental education, and parents’
marital instability, may influence depressive symptoms
through its impact on family stressful events (e.g., having
to move to a different home in order to live within the
confines of low-family income) (Brooks-Gunn and
J Youth Adolescence (2014) 43:1096–1109 1097
123
Peterson 1991; Ge et al. 1994; Wickrama et al. 2008),
extra-familial stressful conditions (e.g., threatening and
dangerous communities; Ross and Mirowsky 2001). Par-
ticularly, resource deprivation (lack of school materials,
food, clothing, and leisure) generates depressive feelings in
youths. These stressful experiences are expected to
increase adaptive challenges for and depressive symptoms
in adolescents already dealing with the rapid biological,
cognitive, and social changes that occur during this period
of life. In addition, as shown in Fig. 1, early socioeconomic
adversity may also be directly associated with adolescent
depressive symptoms.
Depressed youth with weak family ties due to parental
rejection are more at risk for a disrupted transition to
adulthood, particularly, the precocious acquisition of adult
roles (rushed to adulthood; Foster et al. 2008; Scaramella
et al. 1998; Wickrama et al. 2008). Consistent with the life
course perspective, adolescents’ precocious life events
during the transition to adulthood include off-time events,
such as the birth of a child at an early age and truncated
education, that deviate from normative timing, especially
in terms of assuming adult roles or responsibilities while
still an adolescent (Elder et al. 1996). We propose that the
detrimental effect of parental rejection in this chain of risks
experienced by adolescents is stronger than other dimen-
sions of parenting, such as parental management, because
parental rejection operates as a chronic stressor, in addition
to other stressors such as personality and unsafe neigh-
borhoods, and is a source of ‘‘identity disruption’’ with
implications for generating negative feelings (Thoits 1995).
As shown in Fig. 1, regardless of parental rejection and
depressive symptoms, we expect that early cumulative
socioeconomic disadvantage, characterized by a disad-
vantaged family and community, will also contribute to the
occurrence of precocious life events (Bernhardt et al. 2005;
Wickrama et al. 2005). The processes accounting for this
‘‘direct influence’’ may include parental marital problems
(Amato and Booth 2001), parents’ employment problems
(Hagan and Wheaton 1993), family resource limitations
(Lynch et al. 1997), and residential adversity (Wickrama
et al. 2005). Moreover, adolescents from disadvantaged
and troubled families are more likely to form weak bonds
to normative social institutions, such as schools, churches,
and community organizations, due to poor social skills and
low social acceptance, and they also curtail or abandon
conventional aspirations. Consequently, there is less social
deterrence for precocious entry into adult roles (Wickrama
et al. 2008).
The life course perspective suggests that the timing and
sequence of transition events, such as completing one’s
education, beginning a career, and entry into family
responsibilities, gives structure to the life course. Some
studies document that youth benefit from following nor-
mative sequences of major life events (Jackson 2004), but
numerous other studies (Schoen et al. 2007; Shanahan
2000) have shown that youth take a variety of divergent
paths from adolescence to adulthood. We hypothesize that
regardless of this heterogeneity in the timing and sequence
of life events, in general, the early occurrence of major life
transition events may increase the likelihood of negative
consequences for individual well-being because it creates a
chronically stressful life context that places excessive
demands on ill-equipped adolescents (Foster et al. 2008;
Oshri et al. 2011; Wickrama et al. 2008).
Chronic stressful circumstances are thought to lead to
stress responses that may exacerbate metabolic processes
resulting in increased BMI (Dowd et al. 2009). Exposure to
chronic stressors results in a two-stage stress response
(Burdette and Needham 2012). First, adrenaline is released
from the ‘‘fight or flight response,’’ which triggers the
release of stored energy and fat reserves. Second, the
hypothalamic–pituitary–adrenal (HPA) axis is activated to
Fig. 1 The theoretical model: stressful developmental processes
leading to young adult obesity and genetic amplification. Double
arrows signify gene–environment interactions whereby genetic
influences are moderated by early experiences of socioeconomic
adversity and/or parental rejection
1098 J Youth Adolescence (2014) 43:1096–1109
123
release cortisol into the bloodstream in order to restore the
energy reserves by prompting hunger and transforming
food into fat reserves. In addition, psychological distress
may also increase cortisol levels throughout the day lead-
ing to chronically high cortisol levels, which is associated
with central obesity (Burdette and Needham 2012). Psy-
chological distress also contributes to physical inactivity
and the sedentary life style of youth (Katon et al. 2010).
Furthermore, unhealthy eating behaviors are often a way to
cope with stressful life circumstances (Ng and Jeffery
2003; Wickrama et al. 2011). Thus, we expect that cumu-
lative early life socioeconomic adversity will initiate a
‘‘chain of risks’’ including parental rejection, depressive
symptoms, precocious development, and, consequently,
BMI as young adults.
Do Genetic Polymorphisms Amplify Stressful
Developmental Processes?
Additive Genetic Influence (G)
Genetic make-up of an individual represents segments of
the genome that contribute to his/her particular behaviors
(phenotypes) or functions (in this study, acquisition of
precious life events and lifestyle factors, as reflected by
obesity). Polymorphisms are variations in the structure of
genes, and each variant of a gene is called an ‘‘allele.’’
Most molecular genetics research on behavior has focused
on variations in candidate genes that regulate neurotrans-
mitter systems, such as serotonergic and dopaminergic
neurotransmitter systems. Repeat polymorphisms in the
promoter region of SLC6A4 gene produce two variants (or
5-HTTLPR alleles)—a short and long allele—with the
short allele resulting in lower serotonin transporter avail-
ability than the long allele. Research shows that individuals
with one or two copies of the 5-HTTPR ‘‘short’’ allele
display more behavioral, psychological, and health prob-
lems (Caspi and Moffitt 2006). In addition to other relevant
influences on youths’ behavior, serotonin transporter genes
may also play a role in the lifestyle behaviors of young
adults because they are linked to reward sensitivity (Hariri
et al. 2003; 2006; Zhong et al. 2009), which has implica-
tions for precocious life events, such as early sex, early
pregnancy, and early cohabitation, as well as for obesity.
Like serotonin transporter genes, key regulators of the
dopaminergic system (DAT1 and DRD4 genetic variants)
are also linked to reward sensitivity, which has been
hypothesized to serve as the mechanism connecting these
neurotransmitter systems to a host of life processes
including human romantic relations, sexual behaviors,
emotional problems, educational failure, and obesity rela-
ted behaviors (Beaver et al. 2007; Emanuele et al. 2007;
Pederson et al. 2005). Similarly, individuals who have
specific DAT1 and DRD4 allele variants are likely to
engage in novelty seeking behaviors and develop addictive
behaviors, ADHD, and behavioral problems, which may
explain the association between these genetic variants and
precocious development and obesity (Beaver et al. 2007;
Kim-Cohen et al. 2006; Simons et al. 2012). In addition, on
average, individuals with a DRD4 allele variant have been
found to have higher body mass than individuals without
this specific genetic variant (Stice et al. 2010). Thus, we
expect that these genetic variants implicated in both
dopamine and serotonin neurotransmission (5HTTP,
DAT1, and DRD4) may be associated with behaviors
leading to precocious life events (e.g., early sexual inter-
course, teenage pregnancy) as well as to obesity (e.g.,
unhealthy eating and sedentary behavior). More impor-
tantly, recent research indicates that multiple genes may
combine to exert a cumulative influence on individual
behaviors or phenotypes (Belsky and Beaver 2011; Simons
et al. 2012; Wickrama and O’Neal 2013). Thus, we expect
that these genetic polymorphisms will increase the likeli-
hood of youths’ precocious development and high BMI
levels.
Life Contexts–Gene Interactions (G 9 E)
Numerous studies have found that genes, or their variants,
interact with environmental contexts to shape youth
developmental outcomes, such as educational success,
sense of mastery, and health outcomes (e.g., Caspi and
Moffitt 2006; Wickrama and O’Neal 2013). The environ-
ment–gene interaction (G 9 E) has been interpreted
according to a genetic modification approach. From this
approach, the environment is thought to set the stage for a
certain outcome to occur, but whether the outcome mate-
rializes, or to what extent, may be dependent on the pre-
sence of certain genetic variants. That is, genes buffer the
influence of the environment on outcomes or change its
susceptibility to the environment (Belsky and Beaver
2011).
Numerous genetic studies have found that variants of
genes often interact with environmental contexts (G 9 E)
to shape individuals’ psychological vulnerability and aca-
demic and cognitive competency (e.g., Caspi and Moffitt
2006). These findings are often interpreted according to the
stress—diathesis hypothesis, which posits that ‘‘risk
alleles’’ or ‘‘vulnerability genes’’ make individuals more
susceptible to stressful environments (e.g., early socio-
economic adversity) and operate as ‘‘triggers’’ (Shanahan
and Boardman 2009) for negative adolescent develop-
mental outcomes. But the differential susceptibility
hypothesis, or plasticity hypothesis, has emphasized that
positive environmental contexts (e.g., affluent environ-
mental conditions or warm/nurturing parenting) operate as
J Youth Adolescence (2014) 43:1096–1109 1099
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‘‘social enhancements’’ or ‘‘compensations’’ (Shanahan
and Boardman 2009) leading the same genetic variants to
exert positive influences (Belsky et al. 2009; Belsky and
Beaver 2011). In other words, certain alleles may be more
appropriately viewed as ‘‘plasticity genes’’ that merely
amplify the effect of a positive or negative environment.
Although recent studies provide promising evidence for the
plasticity hypothesis (Belsky and Beaver 2011; Simons
et al. 2012; Wickrama and O’Neal 2013), in the present
study, we do not expect to find evidence of such differ-
ential susceptibility because our measures of the contexts
do not capture the full continuum of environmental con-
texts—from positive to negative (e.g., adverse environment
to affluent environmental, warm and caring parenting to
rejecting and neglecting parenting). Rather, our measures
primarily assess environmental adversity and parental
rejection/negligence (i.e., the negative side of the contin-
uum). Thus, in the present study, we expect evidence to
support the stress—diathesis hypothesis because, as shown
in Fig. 1, we expect that genetic polymorphisms will
amplify the influence of age-graded stressful life contexts
on youths’ developmental outcomes (precocious develop-
ment and BMI).
Current Study
Understanding the life course developmental processes
stemming from early socioeconomic context leading to
young adult health outcomes through adolescents’ dis-
rupted transition experiences is a pertinent topic for social
science research. Additionally, investigating genetic influ-
ences on life course developmental processes broadens our
understanding about how biology and environment com-
bine to influence youth development over the early life
course. Previous research has documented the adverse
influence of early socioeconomic disadvantage on adoles-
cent emotional health, the occurrence of youth’s precocious
transition events, as well as their physical health outcomes
(Bernhardt et al. 2005; O’Rand and Hamil-Luker 2005;
Wickrama and Noh 2010; Wickrama et al. 2005, 2008).
However, these studies are often focused on a single pro-
cess and health outcome. Drawing from the life course
perspective, and consistent with the notion of a ‘‘chain of
risks,’’ the present study proposes to examine life course
developmental processes stemming from early socioeco-
nomic adversity leading to young adults’ BMI through
adolescent depression and precocious development.
Because little is known about how genes interact with
social contexts to influence subsequent developmental
outcomes, the present study sought to examine the additive
(G) and interactive (G 9 E) genetic influences on this
process within a single analytical framework (see Fig. 1).
Based on the life course perspective and previous
genetic research, we hypothesized that cumulative early
life socioeconomic adversity will initiate a ‘‘chain of risks’’
including parental rejection, depressive symptoms, preco-
cious development, and, consequently, BMI as young
adults. That is, early socioeconomic adversity will be
associated with increases in adolescents’ depressive
symptoms, adolescents’ depressive symptoms will be
associated with increases in adolescents’ precocious
events, and precocious development will be associated with
increases in young adults’ BMI. In addition, we hypothe-
sized that individuals with certain genetic polymorphisms
(variants of DRD2, DRD4, and 5HTTPR) will engage in
more precocious development and have higher BMI levels
as young adults compared to individuals without these
genetic variants. Finally, we hypothesized that genetic
polymorphisms will amplify the influence of early socio-
economic adversity and parental rejection on youths’
developmental outcomes (precocious development and
BMI).
Methods
Sample
Data for this study were drawn from a nationally repre-
sentative sample of adolescents participating in the
National Longitudinal Study of Adolescent Health (Add
Health). In 1995, baseline (Wave 1) data were derived from
a complex cluster-sampling of middle and high school
students, yielding 20,745 respondents of 12–19 years of
age (average age was 15.5 years), from 134 middle and
high schools. To ensure diversity, the sample was stratified
by region, urbanicity, school type (public vs. private),
racial composition, and size. Second and third wave data
were collected in 1996 and 2001 (N2 = 14,738 and
N3 = 15,100). We used in-home interview data from par-
ents who responded to family demographic, socioeco-
nomic, and parenting questions in Wave 1 and adolescents
who participated in all four waves and provided a genetic
sample. Thus, the final study sample was 12,424. We used
Wave 1 sample weights in the analyses. In most instances,
the adolescent’s mother served as the responding parent
because Add Health investigators rationalized that,
according to the results of previous studies, mothers are
generally more familiar than fathers with the schooling,
health status, and health behaviors of their children. If the
mother was unavailable, the interviewer was instructed to
choose the first person who lives with the respondent from
the following list: stepmother, other female guardian,
father, stepfather, other male guardian. Over 95 % of the
responding parent figures in the final sample were
1100 J Youth Adolescence (2014) 43:1096–1109
123
biological, step, adopted, or foster parents (rather than
another relative or unrelated guardian). More information
about Add Health is available at http://www.cpc.unc.edu/
projects/AddHealth. The final sample consisted of
approximately 53 % women, and 39 % of respondents
reported a minority racial/ethnic status with the largest
percentages reported for African American, Hispanic,
Asian, and Native American, respectively. At W3 or W4
respondents were asked to provide a saliva sample for
genotyping.
Measures
Body Mass Index
At W4 (2008), trained interviewers measured respondents’
height and weight. From these measurements, BMI, the
ratio of weight to height squared ([lbs 9 703]/in.2), was
calculated. Height and weight measurements were also
obtained by trained interviewers at Wave 2 (1996). This
information was used to calculate adolescent BMI, the ratio
of weight to height squared ([lbs 9 703]/in.2), which was
included in the model as a control variable.
Cumulative Socioeconomic Adversity
Following existing research (Brody et al. 2013), we con-
structed an index assessing cumulative socioeconomic
adversity by adding dichotomous indicators capturing dif-
ferent dimensions of adversity. These indicators included
low parental education, high family economic hardship,
low parental marital stability, and high community adver-
sity. Except for marital stability (initially computed as a
dichotomous variable), dichotomous indicators were cre-
ated by conducting a mean split for each of the following
measures.
Parental Education The responding parent reported both
parents’ highest level of education obtained at W1 (1995).
Responses ranged from: 1 = never went to school to
10 = professional training beyond 4-year college or uni-
versity degree. Mothers’ and fathers’ educational levels
were summed to create an index of parental education. For
single-headed families with no available data from fathers
(n = 79), maternal education served as the indicator of
parental education.
Economic Hardship Five dichotomous items (0 = no,
1 = yes) assessed whether any member of the household
received the following social service benefits: social
security, supplemental security income, aid to families with
dependent children, food stamps, or housing subsidies at
W1 (1995). Responses to these five items were summed to
create an index of economic hardship with a range of 0–5.
Parents’ Marital Stability A binary variable was com-
puted to differentiate parents who had been consistently
married to their spouse (or in a marriage-like relationship)
for at least 15 years (1) from other parents (0).
Community Adversity The community adversity measure
was generated by summing four indicators corresponding
to their census tract information from the 1990 US Census.
Those indicators included the proportion of families living
in poverty, the proportion of single-parent families, the
proportion of adults employed in service occupations, and
the proportion of unemployed men (adapted from Sucoff
and Upchurch 1998). This index had an internal consis-
tency of .78.
Parental Rejection and Negligence
Mothers responded to five items assessing their relationship
with the target adolescent. All items were rated on a scale
ranging from 1 = strongly agree to 5 = strongly disagree.
Sample items include whether they ‘‘got along well with
the adolescent’’ and ‘‘felt this child interferes with his/her
activities.’’ When necessary, responses were reverse-scored
before summing the items so that higher scores indicate
greater parental rejection. This index had an internal con-
sistency of .96.
Depressive Symptoms
From Wave 1 (1995) data, eight of the ten items from the
Center for Epidemiological Studies Depression Scale
(Radloff 1977) were used to assess adolescent respondents’
frequency of distress feelings (e.g., ‘‘felt depressed and
sad’’) in the past week. The two positive affect items were
removed to assess the frequency of negative affect only.
Scale responses ranged from 0 (never or rarely) to 3 (most
of the time or all of the time). This resulted in an index of
depressive symptoms ranging from 0 to 24, with adequate
internal reliability (a = .78).
Precocious Transitions
We used both Wave 3 and Wave 4 data to identify
respondents who experienced precocious events. In this
classification, we ensured that all respondents had aged
enough to have experienced risks defined as precocious
events. We operationalized most of the youth’s precocious
life events (e.g., early sexual activities, early marriage,
early cohabitation, early leaving home, and truncated
education) based on US national norm ages, and the events
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that occurred before the normative ages were considered to
be precocious (Wickrama et al. 2005). A sum score was
then computed indicating the total number of precocious
transitions the adolescent experienced. The individual
indicators used in this index are described below.
Early Sexual Activities (Early Sex) In the United States,
the average age of first sexual intercourse was 16 years old
among American males and female (Centers for Disease
Control and Prevention 2010). The onset of sex intercourse
before 16 years of age was categorized as ‘‘early sex.’’
Retrospective reports of respondents’ (Wave 3, 2001) year
of first sexual intercourse and their age were used for this
classification.
Early Marriage Marriage before 24 years of age was
categorized as ‘‘early marriage.’’ Retrospective reports
(Wave 4, 2008) on marital status (married once or more),
duration of marriage, and the respondents’ age were used to
identify young adults who married before 24 years of age.
We also identified and added respondents who reported
their marital experience before 24 years of age in Wave 3,
but did not report it in Wave 4.
Early Leaving Home Previous studies have documented
that the average age of leaving home is 21 years for young
adults (Kreiter 2003). Reports (Wave 3, 2001) on the res-
idential status (living in a separate house, apartment, trailer
home, or group quarters) and the retrospective reports on
the year of moving were used for this classification (these
reports were not available in Wave 4). Full-time college/
university students were not categorized as ‘‘early leavers.’’
Because the youngest respondents were 19 years old in
2001, the cutoff for this classification was 19 years of age.
Thus, our measure corresponds to ‘‘early leaving home’’
during adolescent years.
Early Pregnancy Teenage pregnancy (during adoles-
cence) was considered early pregnancy. Thus, early preg-
nancy (females becoming pregnant or males impregnating/
fathering) before 19 years of age was classified as ‘‘early
pregnancy.’’ Retrospective reports (Wave 3, 2001) on the
year of first pregnancy or ‘‘fathering’’ were used for this
classification.
Joining the Workforce Prematurely Retrospective reports
(Wave 3, 2001) on the year of ‘‘first full-time paid work’’
and respondent’s age were used to identify youths who
worked full-time during the high school attending years.
Truncated Education Adolescents who did not complete
high school or an equivalent level of education (early
termination of education) were classified as having low
education compared to other youth using Wave 3 data.
Composite Genetic Index
The Institute for Behavioral Genetics at the University of
Colorado conducted the genotyping of Add Health DNA
samples using previously established methods (Harris et al.
2006). Three genetic polymorphisms were examined in the
current study because of existing research suggesting spe-
cific alleles of these polymorphisms are related to genetic
risk (Belsky et al. 2009). Specifically, subjects were gen-
otyped for: a 40 bp variable number of tandem repeats
(VNTR) in the 30 untranslated region of the gene (DAT1), a
48 bp VNTR in the third exon of the dopamine D4 receptor
gene (DRD4), and a 43 bp addition/deletion in the 50 reg-
ulatory region of the serotonin transporter gene (SLC6A4).
The specific alleles include the 10R allele of DAT1, the 7R
allele of DRD4, and the short (S) 5HTTLPR allele of
SLC6A4 (12 bp repeat). Following existing research (e.g.,
Belsky and Beaver 2011; Simons et al. 2012), each of the
three genetic polymorphisms was coded dichotomously
(1 = at least one allele, 0 = no copies of the allele), and a
sum score was computed with values ranging from 0 to 3.
Higher scores indicated the presence of more genetic risk
alleles.
Control Variables
Race/Ethnicity At W1 adolescents reported their race/
ethnicity. Dichotomous variables were then created to
assess African American, Hispanic, Asian, Native Ameri-
can, and White racial/ethnic statuses. The dichotomous
variables for each of the minority statuses were included as
independent variables in the regression equation resulting
in regression coefficients that can be interpreted with ref-
erence to Whites (reference group = Whites). For multi-
racial respondents, only their first choice of race/ethnicity
category was considered. The majority of respondents were
White (63.9 %) followed by African American (15.9 %),
Hispanic (13.2 %), Asian (6.0 %), and Native American
(1.0 %) races/ethnicities. Of the Hispanics in the sample,
48.1 % indicated that they were Mexican–American,
15.5 % indicated Cuban American, 15.8 % indicated
Puerto Rican American, and 20.6 % indicated a different
Hispanic race/ethnicity origin.
Gender Gender was coded as male (0) or female (1).
Analysis
We conducted structural equation modeling (SEM) using
Mplus statistical software (version 6) to test our
1102 J Youth Adolescence (2014) 43:1096–1109
123
hypothesized models. The Mplus COMPLEX command
was used to account for the nested structure of the school-
based design within the Add Health study. Full information
maximum likelihood (FIML) procedures were used to
account for missing data. FIML does not impute missing
values; instead, it estimates model parameters and standard
errors directly from all available data. FIML has been
shown to provide more accurate parameter estimates than
other procedures for handling missing data (Enders 2001).
An attrition and missing data analysis showed that ado-
lescents who participated in all four waves were slightly
younger but otherwise confirmed that there was little dif-
ference between adolescents with missing data in our study
sample and those with complete data. Preliminary analyses
revealed no statistically significant rGE correlations
between our cumulative genetic index variable and the
early cumulative adversity index we examined. This sug-
gests that results indicating a G 9 E interaction between
these variables are not reflective of a gene–environment
correlation. The cumulative genetic index also did not vary
significantly by respondents’ gender. Furthermore,
although the cumulative genetic index was not correlated
with race/ethnicity, we incorporated race/ethnicity within
the model to minimize the possibility of population strat-
ification influencing the results. Gene–environment inter-
actions were tested using the product terms of centered
variables. Model fit was evaluated using the comparative fit
index (CFI) and the root mean square error of approxi-
mation (RMSEA).
Results
Table 1 presents descriptive statistics of the study vari-
ables. Young adults’ BMI (W4, 2008) varied from 15.40 to
68.50. Overall, early socioeconomic adversity was not
severe with respondents’ experiencing an average of 1.58
socioeconomic hardships in early adolescence (Wave 1,
1995). Most parents disagreed with statements indicating
parental rejection (M = 9.45, SD = 2.75). Adolescents, on
average, reported few depressive symptoms (M = 5.40,
SD = 3.57). Generally respondents reported few preco-
cious life transition events (M = .67, SD = .83). The
approximate percentages for each precocious transition
event were: 23.8 % for early sex, 9.3 % for early preg-
nancy, 28 % for early marriage, 27 % for leaving home
early, 11 % for joining the work force prematurely, and
13.2 % for high school drop outs. Figure 2 illustrates the
full model assessing early socioeconomic adversities,
subsequent adverse developmental processes, and amplifi-
cation of these effects by genetic polymorphisms as well as
the interactions of these genes with age-graded social
contexts (G 9 E).
Developmental Processes Influencing Young Adult
BMI
As shown in Fig. 2, we found evidence that cumulative
socioeconomic adversity at Wave 1 (1995) may create a
‘‘chain of risks’’ influencing young adults’ BMI (Wave 4,
2008) after controlling for race/ethnicity, gender, and lag-
ged BMI (Wave 2, 1995). More specifically, cumulative
socioeconomic adversity was associated with parental
rejection (B = .16), which, in turn, was implicated in the
occurrence of depressive symptoms (B = 1.15) and later
precocious transition events during adolescence (B = .21).
Also, precocious transition events were more prevalent
among adolescents reporting depressive symptoms
(B = 1.15). As expected, the stressful nature of precocious
transition events was associated with the increased likeli-
hood of having a high BMI in young adulthood (Wave 4)
(B = .15). Thus, cumulative socioeconomic adversity
created a chain of risks resulting in higher BMI in young
adulthood. However, cumulative socioeconomic adversity
at Wave 1 (1995) also continued to exert direct effects on
adolescents’ depressive symptoms (B = 1.50), their pre-
cocious transition to adulthood (B = .83), and their BMI in
young adulthood (B = 1.03) after accounting for this life
course chain of insults.
Statistically significant findings also existed for adoles-
cent BMI. More specifically, on average, adolescents
experiencing greater cumulative socioeconomic adversity
had higher BMI than individuals experiencing less socio-
economic adversity (B = 1.54, p \ .001). Furthermore,
adolescents with more depressive symptoms and those with
more genetic risk alleles generally had higher BMI values
Table 1 Descriptive statistics of study variables (N = 12,424)
Variables Mean (or
proportion)
SD Range
Cumulative socioeconomic
adversity
1.58 1.11 0.00–4.00
Parental rejection 9.45 2.75 2.00–24.00
Depressive symptoms 5.40 3.57 0.00–24.00
Precocious life transition
events
.67 .83 0.00–6.00
Cumulative genetic
sensitivity (G)
1.85 .12 0.00–3.00
Body mass index (W4,
2008)
29.15 7.53 15.40–68.50
Body mass index (W2,
1996)
23.29 4.58 11.63–51.43
Gender (female) 54.5 %
African American 15.9 %
Hispanic 13.2 %
Asian 6.0 %
J Youth Adolescence (2014) 43:1096–1109 1103
123
at Wave 2 (1996) than adolescents with few depressive
symptoms and risk alleles (B = .07, p \ .001 and B = .12,
p \ .05 for depressive symptoms and risk alleles, respec-
tively). As expected, lagged BMI was a strong predictor of
subsequent BMI in young adulthood (B = 1.13, p \ .001).
Race/ethnicity and gender were also included in the
model as control variables, and some notable demographic
differences were also found. For instance, compared to
Whites, African Americans generally reported higher BMI
as adolescents (B = .86, p \ .001). Similarly, Hispanics
also reported higher BMI during adolescence and young
adulthood (B = .62 and .30, p \ .05, respectively) than
Whites. But Hispanics, as a minority race/ethnicity, were
unique in that they reported less parental rejection than
their White counterparts (B = -.09, p \ .01). All minority
racial/ethnic groups reported more depressive symptoms
than Whites (B = .28, .72, and 1.15, p \ .01 for African
Americans, Hispanics, and Asians, respectively), whereas
African Americans and Asians reported fewer precocious
life transitions than Whites (B = -.09, p \ .05 for African
Americans and B = -.20, p \ .001 for Asians). Females
experienced slightly more socioeconomic adversity
(r = .01, p \ .01), more parental rejection (B = .03,
p \ .05), and higher young adult BMI (B = .40, p \ .001)
but fewer precocious life transitions (r = -.07, p \ .05)
than males.
Furthermore, we also examined potential race/ethnicity
and gender moderation, particularly in regards to differ-
ences in the effect of cumulative socioeconomic adversity
on adolescent and young adult BMI. There were no sta-
tistically significant racial/ethnic differences. Regarding
gender differences, the paths from early adversity to BMI
were statistically significant for females (B = 1.138 and
1.134 for BMI in adolescence and young adulthood) but
not for males (B = .578 and .576 for BMI in adolescence
and young adulthood).
Direct and Interactive Polygenic Effects
After controlling for developmental processes, the cumu-
lative genetic index for genetic variants implicated in
serotonin and dopamine neurotransmission did not directly
influence young adults’ BMI (B = .10) or precocious life
transitions (b = .01). However, individuals with more risk
alleles generally reported more depressive symptoms in
adolescence (B = .09). Furthermore, multiplicative inter-
action terms assessing context–gene interplay (G 9 E)
indicated two statistically significant G 9 E effects. The
index of genetic variants interacted with socioeconomic
adversity to influence young adults’ BMI (b = .13). Fur-
thermore, the genetic index also interacted with parental
rejection to influence the occurrence of precocious life
transition events (b = .04). For both interaction effects, the
presence of risk alleles was associated with the amplifica-
tion of the negative influence stressful contexts (more
specifically, socioeconomic adversity and parental rejec-
tion) exert on BMI. Overall, the structural equation model
including developmental processes, control variables, and
genetic factors explained 49.9 % of the variance in young
adults’ BMI. Model fit indices indicated that the model
provided a good fit to the data [v2(55) = 4,638.466;
CFI = .955, RMSEA = .029].
Fig. 2 Developmental processes leading to young adult obesity and genetic amplifications. Unstandardized coefficients are shown with
standardized coefficients in parentheses. Only statistically significant paths are included. *p \ .05; **p \ .01; ***p \ .001
1104 J Youth Adolescence (2014) 43:1096–1109
123
Discussion
Although previous research has documented the adverse
influence of early socioeconomic disadvantage on youths’
physical health outcomes and the increase in health
inequalities over the early life course (Bauman et al. 2006;
O’Rand and Hamil-Luker 2005; Wickrama and O’Neal
2013), little is known about life course developmental
processes that explain this cumulative process. Particularly,
little is known about sequential life course processes
leading to health outcomes. Moreover, most previous
studies are fragmented and focused on single develop-
mental outcomes. Thus, the present study partly fills this
gap by providing evidence for the persistent influence of
early adversity on young adult BMI through sequentially-
linked adolescent developmental failures. More impor-
tantly, to our knowledge, previous research has not inves-
tigated genetic influences on life course processes, and the
simultaneous gene and environment influences, leading to
health outcomes. Consistent with the stress—diathesis
hypothesis, the present study provides evidence for the
additive and interactive genetic influences on this life
course developmental process leading young adults’ BMI.
Specifically, the present study addressed two main
objectives. First, it examined the disrupted developmental
processes of adolescents following early adversities and
leading to young adults’ high BMI. Consistent with our
expectations, the results showed that children who have
experienced adverse socioeconomic conditions, parental
rejection, and depressive symptoms showed higher levels
of precocious development compared to children who have
experienced less adverse conditions. In turn, precocious
development was associated with high BMI in early
adulthood. These findings are consistent with the life
course notion of a chain of risks over the life course
(O’Rand and Hamil-Luker 2005).
We utilized a composite index of early socioeconomic
adversity to capture various dimensions of adversity. As
expected, this multi-dimensional operationalization of
early adversity provided an effective measure with high
predictive validity in relation to youth developmental
processes, explaining variation not only in parental rejec-
tion but also explaining variation in depressive symptoms,
precocious development, and BMI. Moreover, consistent
with previous studies, our preliminary analysis has also
shown that the developmental risk of cumulative socio-
economic adversity is stronger than the independent effect
of individual dimensions of socioeconomic adversity
(Bauman et al. 2006).
In past research, parental rejection has been found to
inflict psychological vulnerability in youth, resulting in the
precocious development of adolescents (Foster et al. 2008;
Scaramella et al. 1998; Wickrama et al. 2008). In line with
previous findings, adolescents’ precocious development
explained variation in young adults’ BMI (Wickrama and
Noh 2010). Although, we did not elucidate the mediating
mechanisms for this association, behavioral and physio-
logical mechanisms may link stressful precocious devel-
opment to young adult BMI. The behavioral mechanisms
may include substance use, poor eating, inadequate sleep,
and lack of exercise (Knutson 2005; Needham and Crosnoe
2005). The physiological mechanisms likely include stress-
related inflammatory and metabolic dysregulations (Ap-
pelhans et al. 2010; Fagundes et al. 2013). Future studies
should elucidate these mechanisms.
Addressing our second study objective, the results pro-
vided evidence for the possible amplification of adverse
development processes of youth by genetic polymorphisms
through interactions with age-graded life contexts (G 9 E).
The results suggest that genetic polymorphisms may
interact with early socioeconomic adversity and with
parental rejection to explain variability in youth develop-
mental outcomes: young adults’ BMI and adolescents’
precocious development, respectively. These findings are
consistent with the notion that the impact of specific
environments and context–gene interplay on an individual
phenotype may be observed only in a later life stage as
G 9 E effects are salient at different ages and also likely
increase from childhood to young adulthood (Shanahan and
Boardman 2009). Thus, the present study examined these
G 9 E influences by locating them in a comprehensive life
course model that allows environments and genes to ‘‘act in
concert’’ over the life course rather than examining gene–
environment interactions in an isolated manner. Hence,
although genetic influences are small in magnitude, the
statistically significant results of the present study suggest
that genetic polymorphism may both accelerate (G effect)
and amplify (G 9 E effect) disrupted developmental pro-
cesses over the early life course.
Candidate gene studies often provide evidence of small
genetic effects (as indicated by effect sizes). For example, a
recent study by Rietveld et al. (2013) published in Science,
found three alleles (single nucleotide polymorphisms) were
associated with educational attainment with small esti-
mated effect sizes (R2 & 0.02 % per allele). A linear
polygenic score from all measured alleles accounted for
&2 % of the variance in both educational attainment and
cognitive function. These researchers argue that these
findings provide promising alleles for examination in
future research, and their effect size estimates can anchor
power analyses in social science genetics. Similarly, we
believe that the genetic variants investigated in the present
study, and their small but statistically significant influ-
ences, are also useful information for future developmental
studies. In combination, the polymorphisms had a small,
but noteworthy, effect on susceptibility to developmental
J Youth Adolescence (2014) 43:1096–1109 1105
123
risks. When a youth inherits several, or numerous, sus-
ceptibility variants together, they may have a sizable
influence on developmental risk (Falconer and McKay
1995). In the present study, we investigated only three
genetic variants, which have been shown to influence
outcomes, due to data availability. Moreover, social epi-
demiologists have pointed out that a small shift in the
distribution of risk throughout the population or small
effects of a risk can make large differences in the wellbe-
ing/health status of that population (Berkman and Kawachi
2000; Mirowsky and Ross 1992). Thus, the results of
present study suggest that future studies should incorporate
more variants in investigations of cumulative genetic
effects. We believe that the evidence for genetic influences
provided by the present study are substantially important
and also suggests that developmental life course research
should be informed by genetics.
To our knowledge, no previous study has examined such
cumulative genetic influences on developmental processes
over the early life course leading to adult health outcomes.
Because multiple genes can cumulatively influence indi-
vidual behaviors by exerting a shared genetic influence, we
followed existing research using a composite genetic
measure to capture this potential polygenic influence
(Belsky and Beaver 2011). Our findings suggest that mul-
tiple genes, rather than individual genes, additively and
interactively with the environment influence youth devel-
opmental outcomes (Belsky and Beaver 2011). Further-
more, the results of our comprehensive model showed that
the association between two life contexts (parental rejec-
tion and precocious development) was not spurious due to
the common influence of the alleles we measured in the
cumulative genetic index. Similarly, the influence of ado-
lescent precocious development on young adult BMI is not
due either to the common influence of early adversity or to
the common genetic influence captured by our index of
genetic variants implicated in neurotransmission.
We argue that the findings of the present study do not
contradict the life course-stress process perspective (Pear-
lin et al. 2005), rather these findings provide extended
support for this perspective. Like the current research, life
course perspective is largely concerned with the effect of
life context on youth developmental outcomes. Also, one
important tenant of the life course perspective (Elder and
Giele 2009) is that individual characteristics (e.g., indi-
vidual agency) operate as moderators of the influence of
life context over the life course. The current research
incorporates biological characteristics as important indi-
vidual characteristics. Particularly, we argue that individual
genetic make-up can be considered as an individual bio-
logical characteristic that moderates the life course stress
process. Accordingly, the significant G 9 E interactions in
the current findings reflect the moderating (or amplifying)
influence of stressful life contexts thereby accelerating the
life course-stress process. Because of the increased avail-
ability of genetic data in psychosocial research, life course-
stress researchers should extend this line of research to
enhance our understanding of life course-stress process.
Several factors potentially limit the scope and the gen-
eralizability of the results. First, our results may be subject
to false positive associations and a lack of statistical power,
which is often a possibility in candidate gene association
studies. Thus, future studies should attempt to replicate
these findings with larger samples. Second, we did not
examine potential moderating effects of youth academic
and cognitive competencies or psychological vulnerabili-
ties, which can protect youth from the negative influence of
early socioeconomic adversity on young adults’ health
outcomes (Wheaton and Gotlib 1997). Third, our measure
of parental rejection and negligence was limited to the
questions asked of parents at Wave 1, the same time point
used to examine cumulative socioeconomic adversity.
Although these items have been used in previous studies
utilizing the Add Health data and have predicted variation
in numerous subsequent physical and mental health out-
comes (Wickrama et al. 2009, 2013a, b; Wickrama and
Noh 2010), the validity of these items has not been spe-
cifically examined and their internal consistency was
higher than typical (.96). Thus, these limitations should be
taken into consideration when interpreting the present
findings.
Conclusion
The present study makes a valuable contribution to existing
research by providing evidence for an adverse develop-
mental process over the early life course stemming from
early adversity as well as for the additive and interactive
influence of genotype on this process. Adverse socioeco-
nomic conditions appeared to initiate an adverse ‘‘chain of
risks’’ including parental rejection, depressive symptoms,
and precocious transition events. In turn, precocious
development was associated with high BMI in early
adulthood. Furthermore, the results suggest that genetic
polymorphisms may interact with early socioeconomic
adversity and parental rejection to influence life course
developmental processes.
In addition to advancing scientific research, these find-
ings have key policy and program implications as they
indicate numerous leverage points for intervention and
prevention work. For instance, it is imperative that policies
are enacted to improve the economic conditions of families
with young children because early socioeconomic adver-
sity initiates a chain of risks that increase the likelihood of
poor health later in life and across multiple domains. The
1106 J Youth Adolescence (2014) 43:1096–1109
123
findings also highlight adolescent depression as a key
leverage point for improving the health of young adults as
depressive symptoms in adolescence are often a gateway to
more severe hardships in later life, including social diffi-
culties, lack of employment opportunities, and poor mental
and physical health (Fombonne et al. 2001; Richardson
et al. 2003). Youth programs and policies should promote
youth psychological competencies that aid in their suc-
cessful transition to young adulthood. In addition, these
findings linking precocious development to young adults’
BMI illustrate the far-reaching positive health conse-
quences of policy and program initiatives aimed at
enhancing successful adolescents’ transition to adulthood
avoiding precocious life events (including early sexual
activity, teenage pregnancy, and school dropout). Particu-
larly, programs and interventions aimed at improving the
life conditions of youth experiencing precocious life
events, such as GED classes or parenting classes for
teenage parents, may be successful turning points whereby
interventions can improve the resilience of these individ-
uals who are at high risk of subsequent poor health, par-
ticularly obesity.
Acknowledgments This research uses data from Add Health, a
program project directed by Kathleen Mullan Harris and designed by
J. Richard Udry, Peter S. Bearman, and Kathleen Mullan Harris at the
University of North Carolina at Chapel Hill, and funded by grant P01-
HD31921 from the Eunice Kennedy Shriver National Institute of
Child Health and Human Development, with cooperative funding
from 23 other federal agencies and foundations. Special acknowl-
edgment is due Ronald R. Rindfuss and Barbara Entwisle for assis-
tance in the original design. Information on how to obtain the Add
Health data files is available on the Add Health website (http://www.
cpc.unc.edu/addhealth). No direct support was received from grant
P01-HD31921 for this analysis.
Author contributions K.A.S.W. conceived of the study, conducted
the preliminary analyses, and drafted the manuscript; C.W.O. par-
ticipated in the interpretation of the data and manuscript writing and
preparation; A.O. helped to draft the manuscript. All authors read and
approved the final manuscript.
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Kandauda A. S. Wickrama is a Professor at the University of
Georgia in Human Development and Family Science. He received his
doctorate in Sociology from Iowa State University. His major
research interests include social determinants of health and health
inequality across the life course and the application of advanced
statistical methods to social epidemiology.
Catherine Walker O’Neal is a Postdoctoral Research Fellow at the
University of Georgia in Human Development and Family Science.
She received her doctorate in Child and Family Development from
the University of Georgia. Her major research interests include
development over the life course and family and social factors that are
influential in health and well-being outcomes.
Assaf Oshri is an Assistant Professor at the University of Georgia in
Human Development and Family Science. He received his doctorate
in Developmental Psychology from Florida International University.
His major research interests include the study of developmental
processes that underlie the link between early stress and risk
behaviors among youth using a developmental psychopathology
theoretical framework.
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