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The Adverse Childhood Experiences (ACE) Study, which created the definition of adverse childhood experiences, is one of the most famous studies that has been conducted in the past decades. Some have called it the “psychological theory of everything,” creating a substantial new line of research. 

The study’s origins date back to 1985. Vincent Felitti, one of the primary authors, worked at Kaiser Permanente in San Diego in an obesity clinic. One of his success stories was helping a woman go from 408 to 132 pounds in about a year.

He saw this woman a few months later and was shocked to find that she had gained more weight in the preceding months than he thought was possible. He gently questioned the woman to find the reason for this and found that her lost weight had gained the inappropriate attention of a male coworker, and he had begun to flirt with her.

This flirting had triggered anxiety, and to ease her anxiety, she began to engage in high levels of binge eating. Felitti probed more and found out that the flirting had triggered her because of a history of incest with her grandfather. The flirting had triggered memories of that abuse. 

This conversation made Felitti curious, and he began to ask some questions of his patients. He found that many of the patients in this program had a history of sexual abuse and other family trauma and, like this patient, had used binge eating to cope with their emotional distress. He found that he had been treating a symptom, not the root cause for some of his patients. 

Felitti presented his findings at a conference and met Robert Anda from the CDC, the other primary author of the ACE study. Their partnership created the ACE study. 

The study’s authors used data from the medical exams and questionnaires the study participants completed at Kaiser Permanente. The two also created a list of eight questions to ask participants about their exposure to adverse childhood experiences (ACEs) or potentially traumatic experiences occurring before a person’s 18th birthday. The eight questions asked about:

• Emotional abuse (a parent swearing at, insulting, putting down, or humiliating the participant)
• Physical abuse
• Sexual abuse
• Witnessing intimate partner violence directed towards their mother
• Someone in the household having a mental illness
• Someone in the household struggling with alcoholism or substance use
• Someone in the household going to prison
• Losing a parent to separation, divorce, or abandonment 

Later versions of the study added the following two ACEs:

• Emotional neglect (not feeling loved, important, or special)
• Physical neglect (not having enough to eat, having to wear dirty clothes, or having no one to protect you)

The participants answered yes or no to each question. The researchers then added the number of yeses to create a person’s ACE score.

The results of this study were staggering. Two-thirds of the sample had experienced at least one ACE, and one-sixth of the study had experienced four or more. And, if a person experienced one ACE, they were more likely to have experienced more.

When looking at the individual ACEs:

• 1 out of 10 participants had experienced emotional abuse
• Over 25% of the participants had experienced physical abuse
• 28% of the female participants and 16% of the male participants had experienced sexual abuse.
• 1 out of 8 participants had witnessed intimate partner violence directed towards their mother.

Additionally, when looking at the relationship between ACEs and the outcomes examined in the medical questionnaires, they found that a higher ACE score was associated with a higher likelihood of the following:

• Having learning or behavioral problems in school
• Workplace absenteeism
• Financial problems and a lower income
• Depression
• Suicide attempts
• Cancer
• Alcoholism and substance use disorder
• Smoking
• Obesity
• Unintended pregnancy
• Having multiple sexual partners
• STDs
• COPD
• Heart disease
• Liver disease 

The finding that ACEs could explain so many physical health and mental health problems and risky behaviors started a new line of research, diving deeper into these relationships. Some of these new studies have proposed other potential ACEs, including:

• Bullying
• Low socioeconomic status and economic hardship
• Neighborhood violence
• Kidnapping
• Being involved in foster care
• Experiencing racial/ethnic discrimination 
• Witnessing a physical injury

More recent research shows that 63.9% of US adults have experienced at least one ACE, and 17.4% have experienced four or more.

This research also suggests the following prevalences for individual ACEs in the US population:

• Emotional Abuse: 34%
• Physical Abuse: 23.3%
• Sexual Abuse: 12.6%
• Witnessing Intimate Partner Violence: 17.2%
• Household Substance Use: 26.5%
• Household Mental Illness: 17.3% 
• Parental Separation and Divorce: 28.4%
• Incarcerated Household Member: 8.6%

• In her book Childhood Disrupted, Donna Jackson Nakazawa provides an extensive overview about the effects of ACEs. I recommend picking up a copy if you want to significantly increase your knowledge about ACEs.
• In his book The Body Keeps the Score, Bessel van der Kolk dives into research about the impacts of all types of trauma. One of the chapters specifically deals with childhood trauma. I recommend picking up a copy if you want to learn more about the effects of trauma

Since the publication of the ACE study, many studies have investigated the effects of ACEs further. You can read more about these findings in the following articles: