Recent research has shed light on the intricate link between area deprivation and brain health, revealing that individuals residing in disadvantaged neighborhoods are more likely to experience poor brain health, including decreased brain volume. This article delves into the mechanisms that underlie this connection, with a particular focus on obesity as a potential pathway.
Additionally, we explore the role of chronic stress in exacerbating this relationship. Finally, we examine the impact of neighborhood disadvantage, high body mass index (BMI), and chronic stress on cortical microstructure, offering a comprehensive view of the intricate interplay between these factors.
Neighborhood Disadvantage and Health Outcomes
Area deprivation, often quantified by the Area Deprivation Index (ADI), has been consistently linked to worse health outcomes. One of the most striking associations discovered is the correlation between living in a disadvantaged neighborhood and decreased brain volume. This revelation raises crucial questions about the mechanisms that drive this relationship. Although the exact causal pathways remain elusive, research has identified obesity as a potential key player.
Obesity as a Mediator
Poor-quality foods, often high in trans-fatty acids (TFAs) and sodium, contribute to this increased risk. TFAs, commonly found in fried fast food, have a well-established connection to obesity, particularly abdominal obesity. Chronic neighborhood stressors, which elevate allostatic load, can also influence eating behaviors, leading to a preference for highly palatable but unhealthy foods as a coping mechanism. This phenomenon has been well-documented in numerous neuroimaging studies, which illustrate how stress can reshape brain structure and function, prompting cravings for unhealthy foods and subsequently increasing the risk of obesity.
The Mediating Role of BMI
High BMI, as a consequence of obesity, emerges as a significant mediator in the relationship between living in a disadvantaged neighborhood and reduced brain volume. This suggests that BMI plays a critical role in amplifying the negative impact of neighborhood disadvantage on brain health. It underscores the importance of addressing obesity as a key factor in mitigating these adverse effects.
Cortical Microstructure and Brain Health
Moving beyond the macroscopic brain changes associated with neighborhood disadvantage, researchers have started investigating the impact on cortical microstructure. This is assessed through the T1-weighted/T2-weighted (T1w/T2w) ratio, which is believed to reflect intracortical myelin content, although its specificity remains a subject of debate. Nevertheless, this ratio has proven valuable in understanding cortical maturation patterns and cognition.
Microstructure Variations Across Cortical Layers
The cortex comprises distinct layers, each with unique cell populations, inputs and outputs, and information processing functions. Upper cortical layers (layers 1-3) feature myelinated inhibitory parvalbumin-positive basket cells, crucial for gamma network oscillations that support various cognitive processes.
Deeper cortical layers, on the other hand, consist predominantly of myelinated non-gamma-aminobutyric neurons that integrate numerous synaptic inputs. Examining microstructure variations across these layers provides insights into how adverse or stressful environments, such as living in disadvantaged neighborhoods, impact cell populations, processes, and communication routes.
In our study, we sought to uncover the intricate relationship between the Area Deprivation Index (ADI), cortical microstructure (as measured by the T1w/T2w ratio) at multiple cortical levels, and potential mediators such as BMI and stress. We hypothesized that worse ADI would be linked to higher BMI, an obesogenic diet characterized by high TFA intake, and increased stress levels, all of which would collectively exert negative effects on cortical microstructure in regions associated with reward processing, emotion regulation, and cognition.
Our findings supported these hypotheses. We observed that worse ADI was associated with higher BMI, increased TFA intake, and heightened perceived stress levels. Furthermore, we noted a nuanced impact on cortical microstructure. In particular, we observed decreased T1w/T2w ratios in middle/deep cortical levels within supramarginal, middle temporal, and primary motor regions. Conversely, we found increased T1w/T2w ratios in middle/superficial cortical levels in medial prefrontal and cingulate regions. Importantly, this latter effect was partially mediated by increased BMI and positively correlated with TFA intake.
In conclusion, living in a disadvantaged neighborhood is intricately linked to worse health outcomes, including adverse brain health and altered cortical microstructure. The mechanisms driving this relationship are multifaceted, with obesity and chronic stress playing pivotal roles.
By understanding these complex interactions, we can begin to develop targeted interventions and policies aimed at improving the health and well-being of individuals living in disadvantaged neighborhoods. Furthermore, exploring cortical microstructure offers a promising avenue for further research, shedding light on how adverse environments impact the very essence of neural communication and cognition.
reference link : https://www.nature.com/articles/s43856-023-00350-5