Childhood abuse is associated with accelerated biological aging and a tendency to avoid looking others in the eye. A new study published in PLOS One shows that these physical and behavioral changes occur independently in abused children. Both of these responses map to higher rates of emotional and behavioral difficulties, giving researchers a better idea of how early trauma shapes human development.
Biological aging can occur at a different pace than chronological aging. One way scientists measure biological age is by looking at epigenetics. Epigenetics involves chemical modifications to DNA that change how genes are expressed without changing the underlying genetic code. Specifically, researchers are focusing on DNA methylation, the process by which small molecular tags attach to specific parts of the genome. As a person ages, the pattern of these tags changes in a predictable way.
In recent years, researchers have developed epigenetic clocks that use these methylation patterns to estimate a person’s biological age. Extreme stress and trauma are associated with accelerated epigenetic aging in adults. Adverse experiences during childhood can cause the body to mature more quickly to cope with an unstable environment.
Measuring accelerated aging in very young children presents challenges. Older epigenetic clocks were designed for adult tissues and were often unreliable when used in pediatric populations. To solve this, researchers developed a pediatric oral epigenetic clock. This tool was designed to accurately estimate aging in children using cells safely and painlessly collected from the inside of the cheek.
In addition to physical changes, childhood trauma can change the way people interact with their environment. People who have experienced trauma or social anxiety often exhibit different visual habits. Avoiding eye contact is a common response to severe stress. By looking away, a person may try to escape a threatening social interaction. Because looking into someone else’s eyes is an important part of building emotional bonds, avoiding eye contact can hinder the development of social skills over time.
Keiko Ochiai led a team of scientists to investigate these physical and behavioral factors together. Mr. Ochiai is a researcher affiliated with the Osaka University United Graduate School of Child Development in Japan. The research team wanted to see whether changes in epigenetic clocks and differences in eye contact occur together, or whether they trigger each other. They specifically wanted to study children whose traumatic experiences had been officially documented, rather than relying solely on adults’ memories of childhood trauma.
Researchers recruited 36 children who had experienced physical abuse, emotional abuse, or neglect. These children had been legally removed from the custody of their biological parents by Child Protective Services. At the time of the study, they were living in a residential child care facility and had an average age of approximately 6 years. The researchers also recruited 60 typically developing children from the community, with an average age of about 4 to 5 years, as a comparison group.
To assess the children’s well-being, the researchers relied on standard psychological assessments. Caregivers and parents completed a strengths and difficulties questionnaire. The survey asks caregivers to rate their children on a variety of attributes, including emotional symptoms, peer relationship problems, and prosocial behavior. By aggregating these reports, researchers were able to get a broader picture of how well each child was adapting to their social environment.
To measure biological aging, the researchers took cheek swabs from all the children. They extracted DNA from the cells that line the inside of the cheeks. The team then analyzed the location of thousands of molecules on the DNA to read the methylation tags. They calculated each child’s biological age using the pediatric clock formula. The researchers then compared this biological age to the child’s actual chronological age to calculate whether the child would age faster.
The researchers also assessed how the children processed social information. They had each child sit individually in front of an eye-tracking monitor in a quiet room. Children underwent a simple conditioning process in which they tracked an animated animal on a screen. The screen then played a short video featuring various social cues. These videos included human figures, geometric patterns, biological movements of the human body, objects with pointing gestures, and human faces.
As the children watched the video, the device recorded exactly where they were looking. The team divided the screen into specific areas of interest. They designated highly social areas such as the eyes of the human face and the upright figure of a person. They also looked at non-social areas such as the mouth of the face and the background regions of the video. The system measured how much the child’s gaze was focused on these specific areas.
Analyzing genetic data, researchers found that abused children experience accelerated biological aging compared to typically developing children. The epigenetic clocks of abused children were ticking faster than their actual age. The researchers noted that although the overall magnitude of the difference was modest, even small changes in biological aging in early childhood can have cumulative effects later in life, such as the earlier onset of puberty.
Eye-tracking data reveals specific differences in how children view human faces. Children who were abused spent less time looking at the eyes on the face on the screen. Instead, their gaze changed further in other areas such as the mouth and the background. The two groups did not differ in how they viewed other types of social cues, such as body movements or pointing. The behavioral changes were highly specific to human faces.
The researchers investigated whether specific details of children’s trauma histories influenced these outcomes. They looked at the type of abuse, the duration of the abuse, and the amount of time that had passed since the children were removed from the home. None of these specific historical factors changed the degree of biological aging or the amount of time spent looking into the eyes. However, children who had experienced multiple types of maltreatment had higher scores on the Behavioral Difficulties Questionnaire.
The researchers then looked for mathematical relationships between epigenetic data, eye-tracking data, and behavioral questionnaires. They found that less time spent looking into the eyes was associated with faster biological aging. Both of these individual characteristics were also associated with improved scores on the Behavioral Difficulties Questionnaire. This suggests that there is a relationship between your body clock, visual habits, and mental health.
The research team used statistical methods to see if these factors worked like dominoes, with one factor causing the next. They created a model to test whether accelerated aging causes children to avoid eye contact, which causes behavioral problems. The statistical model did not support this chain reaction. Rather, it was shown that accelerated aging and decreased eye contact occur in parallel. Both traits were independently associated with behavioral problems seen in maltreated children.
To explain these parallel effects, researchers note that epigenetic changes can alter the way certain genes influence social behavior. Changes in gene expression can disrupt social development from an internal biological level. At the same time, children who cannot see miss important visual cues. Previous research has linked decreased eye contact to lower levels of oxytocin, a hormone involved in building trust and forming emotional bonds. This lack of attachment experience may result in higher rates of social and emotional difficulties.
The authors note that their study has several limitations. The study design was cross-sectional, examining a single point in time rather than following children over many years. Because of this snapshot effect, researchers cannot say that child abuse directly causes the observed aging and gaze changes. Causation can only be proven through different types of experimental methodologies that track changes as they occur.
The study sample size was relatively small but sufficient for the statistical tests used. There were also age differences between the maltreated children and the comparison group. The researchers adjusted their statistical models to account for this age difference, but the evidence would be stronger by comparing groups of exactly the same age. The researchers also noted that the lack of data on adult populations makes it difficult to know whether these exact structural changes persist into adulthood.
Future studies may follow children over longer periods of time to examine biological aging and how social behavior develops over time. This approach could help scientists determine whether moving children into stable, supportive environments can slow the accelerated epigenetic aging process. It may also show whether early intervention can improve social interactions and restore normal eye contact behavior.
Ultimately, identifying these biological and behavioral markers may help medical professionals assess the health and social needs of young trauma survivors. These structural and behavioral adaptations appear to be closely tied to the instability of the child’s early environment. By reading these biological and behavioral markers, psychologists may one day be able to customize treatments that address both the physical toll of trauma and its everyday social effects.
The study, “Behavioral and emotional difficulties in maltreated children: Associations between epigenetic clock changes and visual attention to social cues,” was authored by Keiko Ochiai, Shota Nishitani, Akiko Yao, Daiki Hiraoka, Natasha YS Kawata, Shizuka Suzuki, Takashi X. Fujisawa, and Akemi Tomoda.
