This document reviews literature on the impact of adverse childhood experiences (ACEs). It finds that ACEs are linked to negative health outcomes later in life through their effects on stress response systems and brain development. ACEs are common, affecting up to 67% of the population, and disproportionately impact low-income communities. The impacts of ACEs are cyclical as they increase risks for future generations. While ACEs have lasting biological and behavioral effects, perception of stress may influence outcomes. More research is needed to understand impacts, develop treatments, and engage communities to address this major public health issue.

1. Impact of Childhood Adversity: a literature review
Gabriel Hardt
SPH 491

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Childhood Adversity and Negative Health Outcomes: A Public Health Problem
Stressors, particularly adverse events, during childhood are linked to the leading causes of
death in the adult population (Felitti 1998). In fact, researchers found a dose-response
relationship between the number of adverse childhood events (ACEs) and the prevalence
of cognitive, behavioral, and physical health problems later in life. This relationship poses
major public health problem for the majority of the US population. The 1998 ACEs study
found that up to 67% of the population reported at least 1 ACE, with over 12.6% reporting
12 or more (Felitti 1998). Risk factors for experiencing ACEs include poverty, parental
mental illness, substance abuse, and maltreatment, all of which often co-occur (Tyrka
2013). The disproportionate risk for low-income children may be a major contributing
factor in the perpetuated poor health outcomes in low-income communities. This paper
will provide an over view of current literature regarding the impact of adverse childhood
events. Published manuscripts were obtained from journals in multiple disciplines,
including public health, psychology, medicine, neurobiology, as well as early childhood and
family studies.
Impacts of Childhood Adversity
In 1998, The ACEs study was published in the American Journal of Preventative Medicine
that revealed a strong associated between adverse childhood events and several of the
leading causes of death in the adult population (Felitti et al.) The study defined adverse
childhood events as emotional, physical, or sexual abuse and household dysfunction during
childhood. A questionnaire was mailed to 13,494 adults who had completed a standardized
medical evaluation at a large HMO. A total of 7 categories were studies: psychological,
physical, or sexual abuse, violence against mother, living with household members who

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were substance abusers, mentally ill, or suicidal. They compared these measures to adult
risk behavior, such as smoking or drinking, health status, and disease. More than half of the
respondents reported at least 1 ACE, and ¼ more than two. They found a dose response
relationship between the breadth of exposure to abuse or household dysfunction during
childhood and risk factors for leading causes of death in adults, including ischemic heart
disease, cancer, chronic lung disease, skeletal fractures, liver diseases, and poor personal
rated health (Felitti et al, 1998).
The degree to which a given stressor affects an individual is complicated, and is dependent
on the type, frequency, and nature of the stressor, co-occurrence with multiple stressors,
and the developmental period when the stress occurs (Tyrka 2013). Stress “toxicity” or
“tolerability” is difficult to measure in humans, as a stressor deemed toxic for one
individual may be completely tolerable for another. The subjective perception of certain
stressors is a major challenge in ACE impact research, and a potential source of
confounding in research about impact, treatment, and prevention (Wade 2014). In order to
move forward with this field of research, the ability to accurately measure the toxicity of a
given stressor for an individual, as well as the most prevalent stressors for a given
community, must be improved.
While the problem of perception and subjectivity poses a challenge for this field, it may also
be the key to developing effective treatment. According to a study conducted by the
University of Wisconsin Madison, stress was only be associated with negative health
outcomes if the participants who perceived stress as a harmful to their own health.
Individuals who reported high stress but did not perceive that stress to be impacting them

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negatively did not experience negative health outcomes, even compared to individuals who
did not report any significant stress in their life (Keller, 2012). This finding, among others,
highlights the potential benefit of altering perception related to stress. This is not to say
that ACEs can be “perceived” as a positive experience, but giving children, or adults who
have experienced ACEs in the past, the tools to reframe their experience may actually help
prevent the negative health outcomes by rebuilding the learned neural circuitry and
emotional response associated with the event (Tyrka 2013).
In order to fully comprehend the negative health outcomes associated with ACEs, research
focused on the neurobiological impact of the stress response mechanism. Exposure to a
stressor for any individual triggers the sympathetic nervous system, and causes an
alteration of physiological systems, including appetite, gastrointestinal activity, sexual
function, increased heart rate, blood pressure, cardiac out put and impaired immune
system functioning and fuel storage. This response is natural and can be beneficial for short
periods of time. However, prolonged stress can alter the physiology, neuroplasticity, and
emotional reactivity for that individual (Tyrka, 2013). For example, chronic stress causes
decreased dendritic density of neurons in the prefrontal cortex and striatum associated
with decision-making abilities, and increased dendritic density in areas of the prefrontal
cortex and striatum associated with habit driven behavior (Science, 2009). In other words,
chronic stress decreases an individual’s ability to conduct flexible decision-making needed
to succeed in every-day life, and increases their tendency to stick to routine, habit driven
behaviors, even if those behaviors are detrimental to the individual’s health.

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Children are particularly vulnerable to stressors due to dependency and cognitive
developmental factors. During development, children are entirely dependent on their
caregivers for their basic physical, social, and emotional needs. Therefore, an adverse
environment in the household completely undermines their ability to access basic needs
required for healthy development. At the same time, a child’s brain is undergoing rapid and
large-scale developmental changes in neural pathways that regulate emotion and behavior
(Tykra 2013). A study published in Nature Science, in accordance with Tykra et al, found
that early caregiving behaviors play a critical role in the normal development of brain
circuits involved in the regulation of stress reactivity, learning and memory,
neuroplasticity, and behavior (2009). Specifically, the study exposed rat pups to high levels
of stress, and then randomized those pups to rat moms that demonstrated frequent licking,
or no licking, post stressful event. They found that even if the adult rat was not the pup’s
biological mother, the pup developed better stress coping mechanisms and resiliency, or
stress immunization, if they were randomized to moms with frequent licking. Furthermore,
those same pups demonstrated high levels of licking behaviors for their own children in the
future compared to those that did not receiving licking (2009).
The authors also examined epigenetic differences between postmortem hippocampus
obtained from suicide victims with a history of childhood abuse and those from suicide
victims with no childhood abuse or controls. They claim that their findings translate the rat
maternal care experiment to human subjects, and suggest a common effect of parental care
on the epigenetic regulation of hippocampal glucocorticoid receptor expression involved in
the ability to cope with stressful situations (McGowan et al. 2009). McGowan et al’s and

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Tykra et al’s findings both demonstrate how ACEs cause humans to suffer long lasting
alterations in neurobiological, behavioral, and social systems (2009, 2013).
Another significant finding of McGowan et al and Tykra’s et al research is the cyclic nature
of childhood adversity. If a child is born into a household that puts them at
disproportionate risk for experiencing an adverse event, such as a low socio-economic
status, they are also likely to lack the support they need to deal with that stressor, and
more likely to engage in risky behaviors that will put their own children at risk for the
same outcome in the future (2009, 2013). In this way, the negative impact of ACEs can be
seen as perpetuating negative health outcomes in low-income communities (Wade 2014).
Kristen Springer, MPH MA et al, The Long Term Health Outcomes of Childhood Abuse: an
Overview and a Call to Action, found that individuals who experience one or more ACE
throughout their lifetime experience a plethora of psychological and somatic symptoms, as
well as psychiatric and medical diagnosis, including but not limited to depression, anxiety,
eating disorders, PTSD, chronic pain, fibromyalgia, chronic fatigue, and irritable bowel
syndrome (2003). Springer’s “Call to Action” emphasized the need to focus medical
attention on the impacts of ACEs, and incorporate routine screening into primary care. Her
team, in accordance with the 1998 ACEs study, found that although most patients want
their doctors to scan for a history of abuse, most physicians admit they do not do so, as they
feel their patient would be uncomfortable discussing such personal information. However,
between 20% to 50% of the patient population in primary care has been exposed to
physical or sexual abuse. Of those patients who are suffering from depression, irritable
bowel syndrome, chronic pain, or substance abuse, as many as 70% were exposed to

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physical or sexual abuse (Springer 2003). Springer’s argument addresses the need for an
“upstream” approach to medicine, in which the medical care shifts attention from treating
the disease in isolation to identifying the underlying causes of the disease to achieve true
population level impact.
The previously outlined impacts of ACEs create systematic barriers to an individual’s
ability to succeed in the educational system, and consequently to obtain economic stability
in the future. In a classroom setting, children from low socioeconomic status backgrounds
were found to have a higher incidence of behavioral problems as compared to the general
population (Huaqing 2003). Behavioral problems and consequent punishment decrease a
child’s confidence and ability to succeed in the classroom, decreasing access to higher
education and economic stability in the future. At the same time, behavioral problems in a
child are intimately linked with parent characteristics, parenting style, and socio-
demographic factors (Huaqing, 2003). For example, children with adolescent mothers at
risk for substance abuse had higher rates of problem behaviors than children enrolled in
the Head Start program for low-income communities (Huanqing 2003). This difference may
be correlated with ACE exposure and access to positive mentors to help process exposure
to adverse events.
Causes
The impact of adverse childhood events is caused by the interaction of socio-economic
factors and individual psychobiological responses. Tykra et al. identified coping behaviors
as the link between negative health outcomes and ACEs, such as smoking, alcohol or drug
abuse, over eating, or sexual behaviors. These behaviors may be consciously or
unconsciously employed for their immediate pharmacological or psychological benefit in

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the face of an adverse experience or past (2014). However, using these mechanisms to cope
with current and past stressors only perpetuates the problem for future generations, as
they effectively increase an individual’s risk for developing a substance abuse, mental
illness, and social conflict in adulthood (Tyrkra 2013). So begins the cycle of childhood
adversity across multiple generations, as an adverse event for one individual may cause
them to develop behaviors that put their own children at risk for experiencing an ACE
(Peterson T, 2013).
Socio-economic factors are a major driving factor for this cycle. For example, Krueger PM
and Chang studied how smoking and inactivity increased the impact of stress for entire
population. They found that low income individuals were at disproportionate risk for
negative health outcomes as all three variables, physical inactivity, smoking, and low socio-
economic status, work independently to increase risk poor health outcomes, and in
combination they create a truly disadvantage proportion of the population (2008). Those
with lower socio-economic status have less access to mental health care, therefore are less
likely to receive the treatment they need to over-come the affects of adversity.
According to Wade et al, more research needs to be dedicated to context specific adverse
events in low-income communities, which are at greatest risk for ACEs and have worse
health outcomes compared to other socio-economic sub groups. The authors conducted
focus groups of young adults in low-income areas to evaluate stressors, and found that the
current evaluation of ACEs does not adequately represent the most vulnerable categories
in those communities. The most common cause for adverse events identified in their study
was substance abuse in the home, followed by community stressors such as neighborhood

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violence, crime and death. The study collected and incorporated personal quotes from
participants about their ACE experiences, and emphasized the need to include the voice of
low-income youth in ACE research: “Our work provides a youth perspective on the concept
of childhood adversity” (Wade, 2014).
Conclusion
The consensus across literature is that early life stressors will significantly increase an
individual’s susceptibility to negative health outcomes. However, three major gaps have
been identified: 1) consensus on what qualifies as an adverse childhood experience, and
furthermore, which of those experiences can justifiably lead to negative health outcomes
(tolerable versus toxic stressors) while still accounting for individualized, subjective
experience 2) how ACEs can be prevented and successfully treated in both the adult and
child population, with specific emphasis on low income communities, and 3) the need to
avoid a “top down approach” and to engage with at-risk communities to identify the most
prevalent stressors. It is encouraging the see the inter-disciplinary research attention this
public health problem is generating, but more community engagement is needed to
successfully leverage research into real interventions and treatment approaches in order to
interrupt the vicious cycle of childhood adversity.

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