Neurobiological pathways linking socioeconomic position and health

Abstract

Across individuals, risk for poor health varies inversely with socioeconomic position (SEP). The pathways by which SEP affects health have been viewed from many epidemiological perspectives. Central to these perspectives is the notion that socioeconomic health disparities arise from an interplay between nested, recursive, and cumulative environmental, social, familial, psychological, behavioral, and physiological processes that unfold over the life span. Epidemiological perspectives on socioeconomic health disparities, however, have not yet formally integrated emerging findings from neuropharmacological, molecular genetic, and neuroimaging studies demonstrating that indicators of SEP relate to patterns of brain neurotransmission, brain morphology, and brain functionality implicated in the etiology of chronic medical conditions and psychological disorders. Here, we survey these emerging findings and consider how future neurobiological studies in this area can enhance our understanding of the pathways by which different dimensions of SEP become embodied by the brain to influence health throughout life.

Figure 1

Conceptual schematic illustrating the multidimensional and multilevel aspects of socioeconomic position (SEP). By convention, objective and subjective indicators of monetary, occupational, educational, and other dimensions of SEP discussed in the present article can be measured at the individual and higher levels of social organization. In the context of epidemiological research, these SEP indicators can be linked to disparities in i) health damaging behaviors adopted by an individual, an individual’s family, or an individual’s proximal social contacts; ii) putative biomediators of disease risk; iii) risk factors for psychological disorders; iv) risk factors for often comorbid chronic medical conditions; and v) markers of pathophysiology and preclinical conditions that are predictive of disease end points. The interacting mechanisms by which SEP affects health disparities are thought to encompass those spanning from genetic to environmental levels of analysis. The present survey emphasizes the role of stress, emotion, and mood circuitries and modulatory neurotransmitter systems of the brain as candidate neurobiological pathways that may embody socioeconomic factors and link genetic to environmental mechanisms to health disparities.

Figure 2

Allelic variation in the regulatory region of the serotonin transporter gene moderates an association between personal socioeconomic indicators and central nervous system serotonergic responsivity. In this study, 139 adults (n = 75 men and 64 women) were administered a neuroendocrine challenge to assess central serotonergic responsivity (plasma prolactin [PRL] response to the serotonin releasing agent, fenfluramine [fen]). Objective socioeconomic position (SEP) was estimated by income and years of education. Regression analyses showed serotonergic responsivity to be predicted by the interaction of serotonin transporter genotype and SEP (p = .018). Hence, individuals of lower income and lesser education had lower peak PRL concentrations post administration of fenfluramine than those higher on these dimensions, but only if they possessed at least one “short” allele of the serotonin transporter gene. Mean baseline-adjusted, log-peak PRL[fen] concentrations are shown as a function of long/long (L/L), long/short (L/S), and short/short (S/S) genotypes among individuals of higher and lower SEP, as defined by median division of the distribution of SEP scores. For reference, comparison values of PRL concentration, back-transformed to the unit of PRL measurement (ng/mL), are listed on the right ordinate (here, standard error bars can be interpreted only with respect to the scale of log-transformed scores). 5-HTTLPR = serotonin-transporter-linked promoter region. Reprinted with permission from Manuck and colleagues (48).

Figure 3

Lower subjective socioeconomic position (SEP), as reflected by a lower self-reported ranking on the MacArthur Scale of Subjective Social Status, was associated with reduced gray matter volume in the perigenual area of the anterior cingulate cortex (pACC) in a cross-sectional neuroimaging study discussed in this article. For illustration, panel A shows the 10-point MacArthur social ladder scale used to assess subjective SEP. In panel B, a statistical parametric map of color-scaled t values is overlaid on an anatomical template brain. This map illustrates the pACC area where lower subjective SEP was associated with reduced gray matter volume across individuals. Plotted along the y-axis in panel C is the standardized (Z score) gray matter volume values for pACC area profiled in panel B. Plotted along the x-axis are ladder rankings from the scale illustrated in panel A (1 = “Worst Off”; 10 = “Best Off”). *p < .001. Reprinted with permission from Gianaros and colleagues (57).

Figure 4

Lower subjective parental socioeconomic position (SEP) predicted greater amygdala reactivity to angry faces in a functional neuroimaging study of young adults. A) Modified versions of the MacArthur Scales of Subjective Social Status used to assess subjective parental SEP. B) Statistical parametric maps projected onto an anatomical template. The maps profile amygdala areas where lower subjective parental SEP predicted greater reactivity to angry faces. C) Plots depicting standardized subjective parental SEP scores (x-axis) and mean-centered, standardized reactivity values derived from left (L, open circles, dashed line) and right (R, closed circles, solid line) amygdala areas in B. Inset in C illustrates exemplar trial of angry faces used to elicit amygdala reactivity. Reprinted with permission from Gianaros and colleagues (73).