Just how does childhood adversity turn into poorer health?

If you’re brushing up on your knowledge of how early adversity influences long-term health, sooner or later you’ll come across the CDC’s page on the Adverse Childhood Experiences Study, that famous 1998 study of Kaiser Permanente members in San Diego that launched a flotilla of news articles and studies on how childhood trauma can damage one’s lifelong health outlook.

On that CDC page, you’ll notice a little pyramid meant to illustrate the basics: A foundation of early adversity ups the odds of chronic disease and “Early Death,” the pyramid’s ominous crown. Between that difficult start and untimely end lies the adoption of risky behaviors and “social, emotional and cognitive impairment.” The same pyramid is included in the original study, but the CDC took the liberty of adding in the words “scientific gaps,” a reminder that our understanding of the links between early adversity, unhealthy behaviors, and early disease and death is still a bit murky.

The standard explanation is that children who are abused or traumatized are more likely to grow into adults who smoke, drink, take drugs and take greater health risks than their more fortunate peers. It’s those behaviors that are precipitating poorer health and premature death. That’s the idea offered by Dr. Vincent Felitti and co-authors in the founding study:

The linking mechanisms appear to center on behaviors such as smoking, alcohol or drug abuse, overeating, or sexual behaviors that may be consciously or unconsciously used because they have immediate … benefit as coping devices in the face of the stress of abuse, domestic violence, or other forms of family and household dysfunction.

But, of course, there are other ways in which kids who endure higher numbers of “adverse events” or ACEs could be more likely to have lousier health outcomes. From the original study, we know that the more ACEs you’ve endured, the lower your education level is likely to be on average. For example, 51 percent of individuals with an ACEs score of zero graduated college, while about 5 percent of those with four or more ACEs did so. We also know education is tightly tied to health outcomes; perhaps the lower education levels of these individuals is helping drive their poorer health and shorter lifespans. And lower socioeconomic status has long been linked to poorer health as well. You can imagine the mental maze this creates for scientists trying to control for a single variable such as trauma while ruling out the overlapping effects of class, education and other “confounding variables.”

But what if the poorer health associated with high levels of trauma or adversity isn’t merely a product of these indirect effects? What if there is a more direct biological link, in which early adversity becomes “embedded” or gets “under the skin,” to cite two often-used phrases?

“Lately, epidemiological studies have shown that ACEs were associated with mortality and health even after adjusting for socioeconomic and behavioral factors, suggesting that a direct biological effect occurring from early life is plausible,” write the authors of a new study, published last week in the Proceedings of the National Academy of Sciences, that attempts to disentangle the pathways by which ACEs lead to poorer health later in life.

That’s intriguing, but “plausible” is a long way from proven. And the study, which took its data from a large British cohort study that tracked individuals from birth in 1958 through age 50, struggled to say whether poorer adult health – as measured by cumulative physiological wear-and-tear – among those who experienced more adversity was the product of some biological change or rather less healthy behaviors and lower socioeconomic status. After all, there are a number of factors working against good health here:

[Me]n who experienced two or more ACEs are more likely to have a lower education level, to smoke and drink at 23 years, and to be less well-off at 33 years. Women were more likely to have a lower education level, smoke, be overweight, and be less well-off.

Other research — Harvard’s Center on the Developing Child has been a leader here – has begun to tease out how negligence, abuse and trauma can trigger a child’s stress response and, without the soothing touches of a protective parent, the child’s hormonal stress system can stay permanently elevated. And that can potentially wreak havoc on brain development and raise the risk of chronic disease later in life. (For some great recent coverage of these issues, see Arielle Levin Becker's recent "Starting Early" series in The Connecticut Mirror.)

But there are still a lot of details that researchers have yet to pin down. The literature consistently tells us that childhood adversity is associated with poorer health as reflected by all kinds of measures. But understanding the exact mechanisms by which that adversity works on a child’s body and brain – or perhaps doesn’t, in the case of more resilient children – is still very much a work in progress.

Photo by 55Laney69 via Flickr.