Combined effect of poverty and inflammation on mortality is worse than expected from separate effects, study reports

By Vijay Kumar MalesuJan 18 2024Reviewed by Danielle Ellis, B.Sc.

In a recent study published in Frontiers in Medicine, a group of researchers investigated whether the combination of chronic inflammation and poverty synergistically increases the 15-year risk of mortality from all causes, heart disease, and cancer in American adults aged 40 and older.

Background 

Systemic inflammation is linked to the development of chronic diseases such as cardiovascular, metabolic, renal, and oncologic conditions, significantly impacting morbidity and mortality. Low-grade inflammation is particularly relevant to cardiovascular diseases (CVD), cancer, and associated risk factors.

High sensitivity C-reactive protein (hs-CRP) is recognized as a potent independent predictor of cardiovascular events. Studies have established a connection between elevated CRP levels and increased mortality risks in various CVDs, including coronary artery disease and cerebrovascular disease. Additionally, risk factors like diet, lifestyle, age, and environmental pollutants contribute to chronic inflammation.

In the United States (U.S.), 37.9 million people (11.6%) lived in poverty in 2021, which adversely affects health, reducing life expectancy and increasing mortality risks. Poverty is also associated with heightened inflammation levels. Further research is needed to unravel the complex interactions between poverty and systemic inflammation and their combined impact on mortality, particularly from heart disease and cancer.

About the study

The present study conducted an analysis of the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2002, which was linked to the National Death Index (NDI) data through December 31, 2019. This survey, representative of the U.S. population, includes surveys, physical examinations, and laboratory assays. The focus was on adults aged 40 and older, using the four-year NHANES data collection period to follow a cohort for 15 years until the end of the available NDI data. This approach enabled a population estimate representative of the noninstitutionalized U.S. population.

The study analyzed adults aged 40 and older from the NHANES 1999-2002 dataset, focusing on inflammation, poverty, and demographics. The National Center for Health Statistics (NCHS) provided deidentified NHANES data linked to the NDI for a retrospective analysis. Inflammation was assessed using CRP levels, with two thresholds: >0.3 mg/dL indicating chronic systemic inflammation and cardiovascular risk, and >1.0 mg/dL suggesting systemic inflammation. Poverty status was determined by the poverty index ratio, considering family income, size, and number of children under 18.

Mortality outcomes, including all-cause, heart disease, and cancer mortality over 15 years, were derived from NDI data. The cohort was segmented into four groups based on their inflammation and poverty status. Analysis using R 4.3.3 took into account NHANES' complex sampling, estimating prevalence for the U.S. civilian noninstitutionalized population. The study performed Cox proportional hazards analysis to evaluate the 15-year mortality risk, accounting for age, sex, and race/ethnicity.

Study results

The study's sample characteristics revealed that 11.4% of the population resides in poverty. This demographic aspect sets the stage for a deeper understanding of health outcomes. The study's analytical approach is analyzed by the Kaplan–Meier curves, which are used to illustrate the relationship between inflammation, poverty, and mortality over a 15-year period. These curves are particularly insightful despite being unadjusted for factors like age and race/ethnicity. They effectively portray the general mortality risk associated with varying levels of inflammation and economic status.

The study utilized two CRP thresholds, 0.3 mg/dL and 1.0 mg/dL, to define high inflammation. Kaplan–Meier curves revealed that at the higher threshold, individuals with low inflammation and above poverty had lower mortality than those with either high inflammation or in poverty. The greatest mortality risk over 15 years was seen in those with both high inflammation and poverty. Adjusted Cox proportional hazard analysis confirmed these trends, showing a similar risk at the lower CRP level regardless of poverty status. However, a synergistic effect on mortality risk was evident at the higher CRP level for those with both elevated inflammation and poverty.

The study's scope extends to specific causes of death, with separate analyses for heart disease and cancer mortality. When inflammation is set at the higher CRP threshold of 1.0 mg/dL, a dramatic increase in mortality risk is evident for individuals experiencing both elevated inflammation and poverty. These individuals face a 127% higher risk of dying from heart disease and a staggering 196% higher risk of cancer mortality over 15 years. These findings highlight a critical intersection of health and socioeconomic factors. The elevated risks associated with the combination of high inflammation and poverty underscore the need for targeted public health interventions.