In the 1980s, the dropout rate of participants at Kaiser Permanente's obesity clinic in San Diego, California, was about 50%; but what was perplexing was that all of the dropouts had been successfully losing weight before they left the clinic. Vincent Felitti conducted interviews with individuals who had left the program, and discovered that a majority of 286 people he interviewed had experienced childhood sexual abuse. The interview findings suggested to Felitti that weight gain might be a coping mechanism for depression, anxiety, and fear. Felitti and Robert Anda from the Centers for Disease Control and Prevention (CDC) went on to survey childhood trauma experiences of over 17,000 Kaiser Permanente patient volunteers. The 17,337 participants were volunteers from approximately 26,000 consecutive Kaiser Permanente members. About half were female; 74.8% were white; the average age was 57; 75.2% had attended college; all had jobs and good health care, because they were members of the Kaiser health maintenance organization. Participants were asked about 10 types of childhood trauma that had been identified in earlier research literature.
The study found the following: Adverse childhood experiences are common. For example, 28% of study participants reported physical abuse and 21% reported sexual abuse. Many also reported experiencing a divorce or parental separation, or having a parent with a mental and/or substance use disorder. Adverse childhood experiences often occur together. Almost 40% of the original sample reported two or more ACEs and 12.5% experienced four or more. Because ACEs occur in clusters, many subsequent studies have examined the cumulative effects of ACEs rather than the individual effects of each. Adverse childhood experiences have a dose–response relationship with many health problems. As researchers followed participants over time, they discovered that a person's cumulative ACEs score has a strong, graded relationship to numerous health, social, and behavioral problems throughout their lifespan, including substance use disorders. Furthermore, many problems related to ACEs tend to be comorbid, or co-occurring. About two-thirds of individuals reported at least one adverse childhood experience; 87% of individuals who reported one ACE reported at least one additional ACE. The number of ACEs was strongly associated with adulthood high-risk health behaviors such as smoking, alcohol and drug abuse, promiscuity, and severe obesity, and correlated with ill-health including depression, heart disease, cancer, chronic lung disease[ and shortened lifespan. Compared to an ACE score of zero, having four adverse childhood experiences was associated with a seven-fold increase in alcoholism, a doubling of risk of being diagnosed with cancer, and a four-fold increase in emphysema; an ACE score above six was associated with a 30-fold increase in attempted suicide. The ACE study's results suggest that maltreatment and household dysfunction in childhood contribute to health problems decades later. These include chronic diseases—such as heart disease, cancer, stroke, and diabetes—that are the most common causes of death and disability in the United States. The World Health Organization remarks that the study's findings, while relating to a specific population within the United States, might reasonably be assumed to reflect similar trends in other parts of the world.