Half of the racial mortality gap is explained by stress and inflammation

Disparities in life expectancy between Black and White populations in the United States remain a persistent public health crisis. A new analysis suggests that a lifetime of accumulated stress and resulting bodily inflammation drives a large portion of this racial mortality gap. The findings appeared in a paper published in JAMA Network Open.

Researchers have sought to understand why Black Americans experience higher rates of chronic illness and earlier death. One prevailing theory involves the concept of “weathering.” This hypothesis posits that constant exposure to social and economic adversity physically erodes health over time. Black Americans often face systemic disadvantages and discrimination that generate chronic psychological pressure. This burden is thought to disrupt the immune system and accelerate aging.

Isaiah D. Spears, a graduate student at Washington University in St. Louis, led the new investigation. Spears worked alongside senior author Ryan Bogdan, who directs the BRAIN lab within the university’s Department of Psychological and Brain Sciences. They aimed to move beyond looking at single stressful events. Instead, they sought to measure the total weight of stress a person carries from childhood into old age.

Spears noted the motivation behind the work in a statement. He said he “saw the stark difference between the rate in which our Black participants in the sample have been dying relative to the white participants.” This observation prompted the team to investigate the biological mechanisms that might connect social experience to physical survival.

The team analyzed data from the St. Louis Personality and Aging Network (SPAN). This longitudinal project recruited late middle-aged adults from the St. Louis metropolitan area. The researchers followed these individuals for a period stretching up to seventeen years. The total sample included 1,554 participants. Approximately one-third of the group identified as Black, and two-thirds identified as White.

The researchers created a cumulative stress score for each person to capture the breadth of their life experiences. This score was not based on a single survey. It combined answers from multiple assessments regarding adverse life events. The team looked at exposure to maltreatment during childhood. They included traumatic events experienced during adulthood. They also accounted for specific stressful life episodes and reported experiences of discrimination.

Socioeconomic status served as another component of the stress score. The researchers factored in household income and education levels. They also looked at the education levels of the participants’ parents. This approach allowed the team to build a comprehensive model of the strain placed on an individual throughout their entire lifespan.

The study also required biological evidence of physical wear and tear. The researchers analyzed blood samples collected from the participants. They specifically looked for two biomarkers of inflammation. One is called C-reactive protein, or CRP. The other is Interleukin-6, or IL-6. These proteins are immune system messengers.

High levels of these markers indicate that the body is in a state of chronic inflammation. Short-term inflammation helps the body heal from injury or fight infection. Chronic inflammation, however, damages tissues and organs over time. It is a known risk factor for heart disease, cancer, and other age-related conditions.

The researchers then consulted the National Death Index to track mortality. They recorded which participants died during the study period and the cause of death. This allowed them to calculate survival times for Black and White participants.

The data revealed a clear pattern regarding survival. Black participants in the study died sooner than White participants. This aligned with national trends regarding excess death in minority populations. The Black participants also had higher scores for cumulative lifespan stress. Their blood tests showed higher levels of the inflammatory markers CRP and IL-6.

The researchers used statistical models to test whether these factors were connected. They found that the higher stress levels and subsequent inflammation were not merely coincidental. These factors statistically explained a large amount of the difference in survival rates.

The model suggested a specific pathway. Identifying as Black was associated with higher cumulative stress. This stress was associated with higher inflammation. Finally, that inflammation was associated with an increased risk of earlier death.

The combined effect of lifespan stress and inflammation accounted for 49.3 percent of the racial disparity in mortality. This means that roughly half of the excess mortality risk observed in Black participants could be attributed to these specific biological and environmental factors. The researchers found that stress alone and inflammation alone also played roles, but the combined pathway was the most explanatory.

Ryan Bogdan explained the biological logic in a press statement. He noted that “If stress becomes chronic, that could be incorporated into one’s homeostasis; you may become less able to mount your biological systems to respond to acute stress challenges and your may be less able to return to a bodily state that promotes regeneration and restoration.”

The study supports the idea that social inequality becomes biological reality. The stress measured in the study likely stems from structural racism. This includes factors such as unequal access to resources, neighborhood segregation, and economic barriers. These systemic issues create a constant background hum of adversity for many Black Americans.

Spears emphasized the physical toll of this environment. He stated, “Over time continued chronic exposure to stress leads to dysregulation and an earlier breakdown of some of the biological systems in the human body.” This breakdown manifests as the chronic diseases that disproportionately kill Black adults.

The authors noted several limitations to their work. The study took place in the St. Louis region. The specific social dynamics and health disparities there might not perfectly represent every part of the United States. The results might differ in regions with different economic or social structures.

The researchers also pointed out that their study is observational. They used statistical methods to infer a pathway from race to stress to death. However, they cannot definitively prove causation. Other unmeasured variables could be influencing the results.

The findings leave approximately 50 percent of the mortality gap unexplained. The authors suggest that other factors must be involved. These could include exposure to environmental toxicants like air pollution or lead. Differences in access to quality healthcare or trust in medical institutions could also play a role. Genetic or epigenetic factors that are influenced by ancestral stress might also contribute.

The study has implications for public policy and healthcare. It suggests that medical interventions alone cannot solve racial health disparities. Treating the downstream effects, such as high blood pressure or heart disease, is necessary but insufficient. The root causes of stress must be addressed.

Bogdan suggested that the work points toward the need for broader societal changes. He said, “Addressing large-scale societal issues requires concerted efforts enacted over time. That needle can be extremely hard to move.”

Policies that reduce structural discrimination could lower the stress burden on Black communities. This might involve economic reforms, housing policies, or changes in the criminal justice system. Reducing the sources of stress could prevent the chronic inflammation that leads to early death.

The researchers also see a need for better medical treatments for stress. Interventions that help the body manage the physiological response to adversity could save lives. This would be valuable while long-term societal changes are being implemented. Bogdan noted, “Stress exposure will always be there – so we need to devote more efforts to understand the mechanisms through which stress contributes to adverse health outcomes so that factors could be targeted to minimize health risks among those exposed.”

The study, “Cumulative Lifespan Stress, Inflammation, and Racial Disparities in Mortality Between Black and White Adults,” was authored by Isaiah D. Spears, Aaron J. Gorelik, Sara A. Norton, Michael J. Boudreaux, Megan W. Wolk, Jayne Siudzinski, Sarah E. Paul, Mary A. Cox, Cynthia E. Rogers, Thomas F. Oltmanns, Patrick L. Hill, and Ryan Bogdan.