According to a new study, the link between early poverty and poor mental health might be partly explained by a hormonal mechanism. This mechanism is proposed to interfere with hippocampal development and lead to disrupted emotion regulation. The findings were published in the Proceedings of the National Academy of Sciences.
Early poverty has been established as a risk factor for developmental issues and has been tied to psychological impairment in childhood and adulthood. Intervention strategies to address these consequences early on are needed. Deanna M. Barch, the Gregory B. Couch Professor of Psychiatry at Washington University, and her colleagues note that in order to design effective interventions, researchers first need to understand the mechanisms behind the link between early poverty and impaired mental health.
The researchers proposed that the hippocampus, a major brain structure situated in the temporal lobe, might be implicated in this pathway. There is evidence that early adversity is linked to dysfunction in the hippocampus, with some studies pointing to decreased hippocampal volume and altered connectivity in the hippocampus. In turn, hippocampal dysfunction has been linked to emotional dysregulation problems and increased risk of depression.
“We know that there is a relationship between children’s early exposure to poverty and deprivation and brain development, but we know less about the reasons why this occurs. Ideally we would simply ensure that no children experience poverty,” Barch told PsyPost. “However, while we are working on this larger society issue, determine how early poverty influences brain development may help us develop ways to reduce the negative impact of poverty.”
The researchers proposed a pathway whereby stress affects the testosterone and dehydroepiandosterone (DHEA) hormones through modulation of the hypothalamic–pituitary–gonadal (HPG) axis. This dysregulation of hormones may then disrupt hippocampal development, leading to impaired emotion regulation and greater risk of depression.
The researchers tested this theory using longitudinal data from an ongoing brain development study involving youth who had been followed since preschool age. The youth had undergone up to four brain imaging scans, four testosterone and DHEA saliva tests, and up to nine assessments of depression and emotion regulation. The researchers focused on subjects with hormonal data, hippocampal volume data, and data concerning poverty level at the start of the study. This left a final sample of 167 youth.
Through a series of analyses, Barch and her team found that early poverty did predict shallower increases in testosterone throughout adolescence, even when accounting for early depression. Early poverty also predicted higher depression scores and worse emotion regulation scores at the last assessment, when the youth were an average of 15 years old. Early poverty did not appear to affect DHEA.
Furthermore, there was evidence that testosterone slopes and mental health outcomes were linked. Steeper increases in testosterone over the years were associated with larger increases in hippocampal growth, as well as decreased emotion dysregulation and lower depression at the last assessment. Finally, it appeared that larger hippocampal volume growth across time was also tied to better emotion regulation.
Through mediation analysis, the researchers found that the effects of early poverty on depression disappeared when taking into account the hippocampal volume slope, the testosterone slope, and emotion dysregulation. This suggests that the relationship between early poverty and youth depression was fully explained by the pathway they proposed where testosterone affects hippocampal volume, which in turn affects emotional dysregulation.
“There are likely many reasons why early poverty is related to children’s brain development and mental health. One of those ways may be through having an impact on hormonal systems that in turn have an impact on the development of brain regions such as the hippocampus that are important for emotion regulation and depression,” Barch explained.
Barch and her team noted that there are likely many ways that early poverty contributes to poor mental health outcomes — possibly involving poor education, poor nutrition, and family circumstances. Their study proposes a hormonal pathway that might be one piece of this puzzle.
“It is difficult in research with humans to make strong claims about causation because we would never want to deliberately exposure children to negative environments. Thus, our research is still primarily about ‘associations’ and we need to do more work to determine causal relationships,” Barch said.
“One way to do this ethically in humans is to focus on enhancement and prevention — if you do things to reduce poverty or adversity in children, can you show that this enhances brain development and reduces the risk for mental health problems later in life. I think there are the next types of studies that we need to do. We know quite a bit now about what is associated with challenges and problems for children — now we need to show what can help and how to prevent negative outcomes!”
The study, “Testosterone and hippocampal trajectories mediate relationship of poverty to emotion dysregulation and depression”, was authored by Deanna M. Barch, Elizabeth A. Shirtcliff, Nourhan M. Elsayed, Diana Whalen, Kirsten Gilbert, Alecia C. Vogel, Rebecca Tillman, and Joan L. Luby.
