We have been studying the long shadow cast by early childhood stress and trauma on health across the lifecourse for a several years now. Much of the literature on this subject points towards multiple pathways potentially linking early life stress to health in adulthood. Our latest paper attempts to explore these pathways in more detail. We wanted to examine the plausibility of a biological link between early life stress and physiological strain on multiple systems – a sort of ‘predisease state’. To do this we used a measure of Allostatic Load which was initially conceptualized by Bruce McEwen and Teresa Seeman in the 1990s.
What is Allostatic Load?
Our environment is highly variable and requires the constant adaptation of our physiological systems in order for us to exist. This physiological adaptation process has been called allostasis (Sterling 1988). Chronic exposures to social or psychosocial stressors are associated with prolonged activation of allostatic systems. This may lead to an allostatic overload with potentially detrimental health consequences. Allostatic load is therefore the price paid by the body over time for adapting to challenges.
What did we find?
We used the excellent 1958 British birth cohort study – the National Child Development Study – where biological measures were obtained from participants in mid-life (around 45 years of age). Based on these data we were able to construct a measure of Allostatic Load. The higher your Allostatic Load, the more likely you are to be under physiological strain and develop poor health.
The cohort study has been collecting detailed data on participants since their birth, including their childhood experiences, socio-economic status and health behaviours across the life span. We examined the relationship between adverse childhood experiences and allostatic load by conducting a path analysis.
Our results show that the relationship between stressful experiences in childhood and allostatic load in adulthood is explained by adult health behaviours (especially smoking), adult socioeconomic status (especially wealth), and adult body mass index (in women). However, an unexplained pathway remains. This pathway is not explained by any of the other variables used in the model. It could suggest that there are factors we did not or could not include in our model that would account for this pathway. It could also represent a ‘direct’ biological pathway between early life stress and adult physiological wear-and-tear.
The possible ‘direct’ biological pathway is rather a difficult one to establish, since we can only really do so by eliminating the other pathways – and of course methodological limitations mean that what is left may be something unaccounted for. However, more and more studies are collecting good quality data where the impact of the social environment on our biology may be examined. It will be important to carry out similar analyses using other studies, to get to grips with the mechanisms at play.
Public Health implications?
This work contributes to a body of literature putting scientific weight behind all types of policies to improve and invest in early life environments. This is an area lacking in investment both in terms of research and policy-making:
“The almost total absence of nationwide data on the developmental progress of very young children may reflect the fact that the importance of early childhood development has only relatively recently been brought to public and political prominence. In part, also, it may reflect the traditional view that the collection of data on the lives of the very young is impractical, potentially intrusive, and of limited relevance to public policy. But in part, also, the problem has been the lack of any widely applicable means of measuring and monitoring children’s developmental progress in the earliest years of life. Without such a measure, policy is blind, expenditure difficult to justify, goals impossible to set, and progress incapable of being monitored”
Next steps for research?
The newly formed Interdisciplinary Health Research subgroup of the Society for Longitudinal and Life Course studies (SLLS) will structure and facilitate work examining studies where social/ psychosocial data are used in tandem with biological data. We hope to elicit discussions on the social-to-biological transition and the embodiment of the social environment via theoretical, methodological and empirical studies. If you are interested in joining please get in touch with me or sign up on the SLLS site.
Sterling P, Eyer J. Allostasis: a new paradigm to explain arousal pathology. In: Fisher S RJ, editors, editor. Handbook of life stress, cognition and health. New York: John Wiley & Sons, 1988:629-49.
McEwen BS, Stellar E. Stress and the individual. Mechanisms leading to disease. Arch Intern Med 1993;153(18):2093-101.
Seeman TE, Singer BH, Rowe JW, Horwitz RI, McEwen BS. Price of adaptation–allostatic load and its health consequences. MacArthur studies of successful aging. Arch Intern Med 1997;157(19):2259-68.
Barboza Solís C, Kelly-Irving M, Fantin R, Darnaudéry M, Torrisani J, Lang T, and Delpierre C. Adverse childhood experiences and physiological wear-and-tear in midlife: Findings from the 1958 British birth cohort Proceeding of the National Academy of Sciences 2015 (published ahead of print February 2, 2015) PDF