The ACEs Study: The Research That Changed How We Think About Childhood and Adult Health

The Adverse Childhood Experiences (ACEs) Study is one of the most influential public health studies of the past thirty years, and it started with a puzzle in an obesity clinic.

How it began

In the 1980s, Dr. Vincent Felitti, who ran a weight-loss program at Kaiser Permanente in San Diego, was frustrated by high dropout rates among patients who were successfully losing weight. When he interviewed those patients, he found a connection he hadn't expected: many described histories of childhood sexual abuse, and for some, weight gain appeared to function as a way of coping with depression, anxiety, and fear.

Felitti partnered with Dr. Robert Anda, an epidemiologist at the CDC, to test whether this pattern held more broadly. Of roughly 26,000 patients seen in Felitti's department, 17,421 agreed to participate in the study, which collected data between 1995 and 1997 across two waves. Participants answered detailed questions about childhood abuse, neglect, and household dysfunction, which the researchers then linked to their adult health records.

What they measured

The study asked about categories of childhood adversity, including recurrent physical abuse, recurrent severe emotional abuse, contact sexual abuse, and growing up in a household where someone was incarcerated, where the mother was treated violently, or where there was substance abuse or mental illness. To make sense of the data, Felitti and Anda developed a simple scoring system: one point for each category of adversity a person experienced, producing an "ACE score."

What they found

ACEs were common. The study population was, in the words of one account, average Americans: Kaiser members with jobs and good health care. Even so, 28% of participants reported physical abuse and 21% reported sexual abuse in childhood, and many reported parental divorce or separation, or a parent with a mental health or substance use disorder.

ACEs clustered. Adversity rarely came alone. Among participants with one ACE, 87% had at least one more.

The effect was dose-dependent. This was the study's most important finding. The more ACE categories a person had, the greater their risk of later health and social problems, including significant increases in alcoholism, heart disease, and cancer. Follow-up research tracking participants over time found that higher ACE scores were also associated with a higher risk of death.

The original findings have since been reported across more than 70 publications, and the questionnaire has been adapted for use in state and national surveys.

What the study got right, and where it has limits

The study's strength was its ability to show that childhood adversity is not a niche problem or a purely psychological one. It reframed things like smoking, overeating, and substance use as potential coping responses to earlier harm, and it brought childhood experience into conversations about heart disease and cancer.

It also has real limitations worth stating plainly:

• The sample wasn't representative. All participants had health insurance, most were middle to upper socioeconomic status, around 74% had attended college, and the sample was predominantly white. Later studies in Philadelphia, Wisconsin, and Washington State, among others, found similar patterns, which strengthens the core conclusions, but the original population was narrower than the U.S. as a whole.

  
  

• The ACE score is a population tool, not an individual diagnosis. Researchers have pointed out that while higher ACE counts correlate with worse outcomes across populations, the simple additive score performs poorly at predicting which individual will be affected. It also treats every ACE as equal and overlooks how different adversities interact.

  
  

• It captures a limited list of experiences. Community violence, poverty, discrimination, bullying, and other stressors weren't part of the original questionnaire, and later versions have expanded it.

  
  

Why it still matters

The lasting contribution of the ACE Study isn't the score itself. It's the shift in the question clinicians, researchers, and policymakers ask: from "what's wrong with this person?" to "what happened to this person?" That shift underlies much of modern trauma-informed care in medicine, mental health, education, and, as covered in earlier posts here, the courts.