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The connections became clear: compared with a person with no adverse childhood experiences, or ACEs, a person with four or more has almost double the risk of obesity. Having four or more ACEs more than doubles the risk of heart attack and stroke, and nearly quadruples the risk of emphysema. The risk for depression is more than quadrupled. Although many of these outcomes could reflect the influences of genes and other environmental influences — beyond those occurring in childhood — the tight relationship between increasing ACE numbers and increasing health risks makes the role of child trauma clear. Dr. Jack Shonkoff, director of Harvard's Center on the Developing Child, calls the research "a tremendous contribution."
But how does the psychological experience of childhood neglect cause physical effects like obesity, heart attack or stroke? There are at least two interconnected pathways — one physiological, the other psychological.
The psychology is relatively straightforward: being abused or otherwise traumatized is painful, and food can be a numbing or comforting escape. Hence, abused children may turn to overeating, which causes obesity. Indeed, ACEs are also strongly linked with other types of unhealthy "self-medication": for instance, cigarette smoking (which accounts for the increased rate of emphysema among high ACE scorers) and drug abuse (having four or more ACEs increases the risk of injectable-drug use by a factor of 10). As Felitti puts it, "Being fat [or having other unhealthy behaviors] is not the problem. It's the solution."
The psychological effects often exacerbate health problems that the physiological stress response has already caused. High ACE scorers who do not overeat, smoke or take drugs still have high rates of obesity, heart disease, depression and diabetes. The mechanism for these risks appears to lie in the biology of the stress-response system and in the way environment affects a person's genetic activity.
For most of human evolution, a stressful world would have been marked by famines or periods of starvation, and that environment might have resulted in a particular pattern of gene expression that would have prompted the body to store more fat in preparation for the next bout of scarcity. Today, of course, the same response to stress would result in obesity. This theory of a thrifty fat-storing system that kicks in under high levels of early stress was originally proposed by British physician David Barker.
If, for instance, a modern child's early life experience — in the womb and during the first five years, particularly — is constantly stressful, it would be incredibly energy-consuming, says Dr. Bruce Perry, senior fellow at the ChildTrauma Academy. "If your genes get the message that you are entering a stressful world, it makes complete adaptive sense to take the existing metabolism and tune it up to deposit fat and store energy to prepare for what the body is expecting will be a challenging and stressful life," he says.
"Early adverse experience can disrupt the body's metabolic systems," says Shonkoff. "One of the cornerstones of biology is that our body's systems when they are young are reading the environment and establishing patterns to be maximally adaptive."
Researchers also posit that high levels of stress hormones caused by ACEs can wear down the body over time. A temporary spike in blood pressure in response to a stressful event may be useful to power an adaptive fight-or-flight response, but over the long term constant high blood pressure could raise a person's risk for heart attack and stroke. Studies have also found that consistently elevated levels of stress hormones, like cortisol, can lead to permanent damage in certain brain regions linked to depression.
Recently, scientists have discovered that these changes can themselves be passed down from one generation to the next — a burgeoning new area of study called epigenetics. Such research may have significant and long-term implications for the prevention of obesity, addiction and other illnesses related to early life stress. After all, reducing childhood exposure to trauma in one generation may further benefit that generation's children and grandchildren.
Some initiatives, such as the nurse home-visiting program and President Obama's proposed Promise Neighborhoods program, already put this theory into practice, by offering support and services to low-income parents in order to reduce child abuse, increase access to prenatal care and provide parenting education and high-quality day care.
The goal is not only to improve conditions for the current participants of such programs, but also hopefully to reduce the risk of problems in successive generations, including major causes of death and disability like obesity, heart disease and stroke. "It's not a secret that there is a growing epidemic of obesity and there's no question that the way we eat and the way we exercise, or do not exercise, is contributing to it. But it's a huge mistake to attribute it just to the need to close down fast-food restaurants and turn off the TV. There's important biology here early in life that needs attention," says Shonkoff.
Szalavitz is co-author, with Dr. Bruce Perry, of the forthcoming Born for Love: Why Empathy Is Essential and Endangered