In recent weeks, much has rightly been written about the forced separation of families and children at the US border. As details of the separations emerged, it became clear that we were witnessing an act of wanton cruelty carried out by an administration that has already done much to mainstream callousness in American life. Many of the detained children were being held in warehouse facilities; some, appallingly, were placed in cages. As former First Lady Laura Bush wrote in The Washington Post, images of these facilities were “eerily reminiscent of the Japanese American internment camps of World War II, now considered to have been one of the most shameful episodes in US history.”
President Trump has since signed an executive order ending the practice of family separation. Questions remain, however, as to whether this apparent resolution is in fact an attempt to undermine the Flores Settlement, which could ultimately give the administration the power to impose indefinite detentions. Nor does the order address how the administration will reunite already separated children with their parents. Either way, it is clear that the separations should never have been allowed in the first place. They were an exercise in moral bankruptcy and betrayed the best values of our country. They also undermined health, a fact which Bush points out in her article: “We also know that this treatment inflicts trauma; interned Japanese have been two times as likely to suffer cardiovascular disease or die prematurely than those who were not interned.” The separations were especially harmful to children, both in the short- and long-term. Health unfolds throughout the life course; exposures in our first years of life can continue to affect our health indefinitely. With this in mind, we today rerun a Dean’s Note about how health is shaped throughout the life course, in the hope that the Trump administration will heed the many voices that spoke out against the separations, and choose not to resume its assault on the well-being of the vulnerable.
A life course approach to health is based on the understanding that multiple factors, including biological, social, psychological, geographic, and economic, shape health over the life course through risk mechanisms that are independent and cumulative and interact over time. As John Lynch and George Davey Smith succinctly put it:
A life course approach to chronic disease epidemiology explicitly recognizes the importance of time and timing in understanding causal links between exposures and outcomes within an individual life course, across generations, and on population level disease trends. (p. 1)
The scope of specific factors covered within this approach includes, for example, physical growth, social mobility, behavior changes, physical environment, and life role transitions. Centrally, life course approaches attempt to assess how exposures arise and produce health throughout life, and how we make sense of these interconnected temporal processes. Life course approaches also extend beyond the life of any one individual to suggest connections in health across generations. Therefore, a life course approach guides us, for example, to this question: How does childhood exposure to a traumatic event—like a child’s forced removal from her parents—change the risk of poor mental health in adulthood? Importantly, a life course perspective suggests that we cannot ignore this question—that is, unless we understand the traumatic event experienced during one’s childhood, our understanding of poor mental health in adulthood is going to remain limited and incomplete.
This raises the conceptual and analytic bar, suggesting that we must take into account factors throughout life, and across generations, to better understand the health of populations at any given moment. This may indeed make our job harder, but it also points to approaches that can yield compelling answers and help us move beyond the welter of contradictory findings that unfortunately characterize much of population health science literature.
The advent of formal thinking about life course approaches in population health science is relatively recent and emerged principally in the realm of chronic disease, although further work has well shown how this approach extends to psychiatric and substance use disorders, infectious disease, and oral health. The most recent precursor to the formalization of a life course approach in population health science came via professor David Barker and colleagues, who found a link between birth weight and lifetime risk for coronary heart disease. Known as the “fetal origins hypothesis,” this work focused on how prenatal programming may influence later health. Prior to this work, it was not entirely clear whether prenatal exposure mechanisms were linked to adult disease only through their correlation with later life exposures, or whether these early exposures mattered entirely on their own. The work of Barker and colleagues showed that these early-life exposures did matter on their own, above and beyond any measured confounding variables. Barker’s example opened the way to the formal introduction of life course thinking in the field in the coming decades.
As our thinking about life course exposures has sharpened, several authors have articulated key mechanistic models that may explain how exposures over the life course shape subsequent health. Key models in this regard are the critical period, sensitive period, accumulation of risk, and chains-of-risk models. The critical period model emphasizes the timing of an exposure during specific periods of unalterable biological development, with the understanding that the exposure can affect that development. One example of this is fetal exposure to teratogens [see Figure 1], which links directly to our understanding of human embryonic development to illustrate how fetal exposure to a particular event or agent can result in subsequent alterations to normal human development.
The sensitive periods hypothesis posits that there are sensitive periods throughout the life course, that are not temporally fixed, during which exposure can have a greater impact than at another time. An example is the effect of poverty on mental health during a period of social transition such as divorce.
In an accumulation of risk model, the total amount of exposure is what matters, rather than specific exposure time points. Nutrition and cancer risk provides an illustrative example [see Figure 2].
Finally, the chains-of-risk model emphasizes the sequence of exposures and assumes that one exposure increases the risk of, or triggers, another exposure. An example of this model is nicotine exposure potentiating cocaine addiction.
Perhaps the greatest challenge in adopting a life course approach rests on how one may operationalize such an approach to our analytic ends. One simplification rests on thinking about discrete life course stages and then considering how each stage can represent causes of later disease, and manifest consequences of prior exposure.
By way of example, we can turn to an area in which I have done a reasonable amount of work: substance use. We can consider a life course epidemiology of substance use by thinking of five life course stages: in utero, infancy, childhood, adolescence, and adulthood.
In utero exposure to smoking is a cause of increased risk of lifetime tobacco dependenceand also carries the immediate consequence of low birth weight. Low family socioeconomic status and marital status changes during infancy predict early onset of smoking, while exposure to parental smoking during infancy is associated with sudden infant death syndrome. Childhood neglect and abuse are associated with binge drinking in adolescence, while maternal drug use during childhood predicts early onset of the same drug use in children. In adolescence, drinking is associated with alcohol dependence later in life, while multiple substance use is a consequence of prior physical and sexual abuse. Finally, in adulthood, low income is positively associated with increased risk of substance use disorders, while injuries are a consequence of alcohol intoxication.
Each of these illustrations well make the point that a life course perspective suggests links across phases of life, and that absent an understanding of these links it will be difficult to understand any particular “one point-in-time snapshot” of population health. These illustrations, however, will also suggest to the reader that this approach, while helping us better understand the determination of population health, raises substantial methodological and conceptual questions that might open up new scientific vistas and challenge dominant paradigms. At the simplest level, why should an exposure in childhood influence health in adulthood? Clearly some process, perhaps biological, perhaps social, must link these life stages. Even more provocatively, why should exposures for one generation influence the health of a subsequent generation? The recent emergence of epigenetics as a potential explanatory has provided some promise in these efforts, although that too perhaps opens up as many questions as it answers. Methodologically, a life course perspective calls for approaches that rise above our typical deterministic approach—that can take into account both long-term temporal influences and the dynamic, discontinuous, and non-linear influences that these approaches likely suggest.
All of this suggests that for all the immediate harm that has been done by the Trump administration, the true health effects of its actions will be far deeper than we can presently see. By creating the conditions for early trauma, the administration has made it likelier that affected children will experience poor health throughout life—just as the interned Japanese did—potentially harming health for generations to come. From the perspective of health—as well as that of basic morality—the practice of family separation undermines America’s present, ignores the lessons of its past, and lays the groundwork for a crueler, sicker future.
Until next week.
Acknowledgement: I would like to acknowledge the work of Gregory Cohen, MSW, on this Dean’s Note and the second Dean’s Note in this series.