Adverse childhood experiences

The original ACE Study mailed a questionnaire to 13,494 adults who had completed a standard medical evaluation, and 9,508 (70.5%) responded. It studied seven categories: psychological, physical and sexual abuse; violence against the mother; and living with household members who misused substances, were mentally ill or suicidal, or had been imprisoned [5]. Later analyses of 17,337 adults used eight categories, adding parental separation or divorce, and summed them into an ACE score [1].

The score has known limitations. It counts categories equally, whatever the severity, frequency or age at which they occurred, and it relies in most studies on adults' memories of childhood. In the Dunedin study in New Zealand, adversity recorded by researchers throughout childhood agreed only moderately with adversity recalled at age 38 (correlation 0.47). Recalled adversity was more strongly associated with self-reported outcomes, and recorded adversity with objectively measured outcomes such as biomarkers [2]. Researchers who developed the score have published an account of its strengths, limitations and misapplications [11].

Estimates of prevalence depend on the population and the categories counted. In the original ACE Study, more than half of respondents reported at least one of seven categories and one quarter reported two or more [5]; in the smoking analysis of 9,215 respondents, 63% reported at least one of eight categories [4]. In Behavioral Risk Factor Surveillance System data from 25 US states collected between 2015 and 2017, 15.6% of adults reported four or more types [3]. In a Danish national register study that measured adversity through official records, almost half of children experienced some degree of adversity [8].

The original study found a graded relationship between the number of ACE categories and every adult risk behaviour and disease examined. Compared with people reporting none, those reporting four or more categories had 4 to 12 times the risk of alcoholism, drug misuse, depression and suicide attempt; 2 to 4 times the risk of smoking, poor self-rated health, many sexual partners and sexually transmitted disease; and 1.4 to 1.6 times the risk of physical inactivity and severe obesity. The number of categories was also related to ischaemic heart disease, cancer, chronic lung disease, skeletal fractures and liver disease [5].

A 2017 meta-analysis (a study that pools the results of earlier studies) of 37 studies with 253,719 participants compared people with four or more ACEs with those with none across 23 outcomes. All outcomes were more common with four or more ACEs. The associations were weakest for physical inactivity, overweight or obesity and diabetes, and strongest for problematic drug use and for interpersonal and self-directed violence [6]. Links with smoking, alcohol and poor sleep are among the most consistent. In the ACE Study, five or more categories were associated with 5.4 times the odds of starting to smoke by age 14 and 2.1 times the odds of current smoking [4], and with 2.1 times the odds of trouble falling or staying asleep [12]. Sleep problems are described under insomnia.

In 17,337 adults from the ACE Study followed from 1995 to 1997 until the end of 2006, 1,539 died. People with six or more ACEs died at an average age of 60.6 years, compared with 79.1 years for those with none. After adjustment for other factors, six or more ACEs were associated with 1.7 times the risk of death by age 75 and 2.4 times by age 65. The increase in risk was not graded across the number of categories, and it was only partly explained by documented health and social problems [1].

Studies that recorded adversity during childhood point in the same direction. In the British 1958 birth cohort, with adversity reported by parents and schools, men with two or more adversities had 1.57 times the risk of death by age 50, and women 1.66 times with one adversity and 1.80 times with two or more. Adult lifestyle factors had little effect on these associations [7]. In Danish registers covering 1,097,628 children born between 1980 and 1998, early material deprivation, persistent deprivation and loss or threat of loss in the family were each associated with 1.38 to 1.80 times the mortality between ages 16 and 34. The 3% of children with multiple adversities throughout childhood had 4.54 times the mortality, or 10.30 additional deaths per 10,000 person-years, and accidents, suicides and cancer were the most common causes of death in this group [8].

Childhood adversity may affect adult health through long-term changes in the body's stress systems. In the Dunedin birth cohort, children who had been maltreated had 1.80 times the risk of clinically relevant C-reactive protein levels 20 years later. The association remained after accounting for other early-life risks (1.58), stress in adulthood (1.64) and adult health and health behaviour (1.76), and more than 10% of cases of low-grade inflammation in the population may be attributable to childhood maltreatment [9]. The role of inflammation in chronic disease is described under inflammation.

A review of stress and cardiovascular disease concluded that severe stress in childhood, such as physical abuse and household substance misuse, can increase the risk of several chronic conditions in adulthood, and that its effects are generally larger than those of stress experienced in adult life [13]. The physiology of stress is described under stress and anxiety.

Positive experiences in childhood are associated with better adult mental health at every level of adversity. In a Wisconsin survey of 6,188 adults, those who recalled six or seven positive childhood experiences, drawn from relationships with family, friends, school and the community, had 72% lower odds of depression or poor mental health than those who recalled zero to two (odds ratio 0.28, 0.21 to 0.39). The association was similar for adults reporting one, two to three, or four to eight ACEs [10]. In adulthood, strong social relationships are associated with 50% higher odds of survival [14], as described under social connection.

Depression that follows childhood maltreatment is more persistent and responds less well to treatment on average. A meta-analysis of 16 studies with 23,544 participants found that maltreatment was associated with 2.27 times the odds of recurrent or persistent depressive episodes, and a meta-analysis of 10 clinical trials with 3,098 participants found 1.43 times the odds of not responding to or not reaching remission with treatment [15]. For post-traumatic stress disorder, the UK National Institute for Health and Care Excellence recommends trauma-focused cognitive behavioural therapy and eye movement desensitisation and reprocessing (EMDR) [16]. Crisis lines and specialist support services for adults affected by childhood abuse or neglect operate in many countries.

Full deep dive: Adverse childhood experiences.

Most ACE research is observational and much of it relies on adult recall, which can be biased by personality [2]. Childhood adversity often occurs alongside poverty and material deprivation, which also affect adult health [8], and the ACE categories are strongly interrelated, so the effect of any single experience is difficult to separate [5]. The original study population was insured adults in one US city, and the mortality results from that population were not graded across the number of categories [1].

The ACE score gives each category equal weight [1] and does not include adversities such as poverty. It summarises differences in risk between groups of people and does not predict the health of any one individual. Prospective studies from the United Kingdom, Denmark and New Zealand confirm the main associations with adult health and mortality, but none can fully separate childhood adversity from the family, social and economic circumstances in which it occurs [7, 8, 2].