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Heterogeneity in the Association Between Anemia and Blood Pressure in a Rural Population

This study of a rural Alabama population reveals that the association between anemia and blood pressure is heterogeneous, varying significantly by race and gender, particularly showing higher blood pressure in anemic African American men compared to their non-anemic counterparts, while the relationship is attenuated or reversed in White men.

Original authors: Sharlene D. Newman, D. Nichole Pompey, Linda Knol, Wanda Burton, Paige Johnson, Letisha Scott, Amie Brunson, Matthew Hudnall

Published 2026-09-29

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CC BY 4.0

Original authors: Sharlene D. Newman, D. Nichole Pompey, Linda Knol, Wanda Burton, Paige Johnson, Letisha Scott, Amie Brunson, Matthew Hudnall

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

High blood pressure is a silent force that shapes the health of millions, often acting as a gateway to heart disease and stroke. It does not affect everyone in the same way; in the United States, Black adults often face higher rates of the condition and develop it earlier in life than White adults, while people living in rural areas frequently struggle with fewer healthcare resources and greater economic hardship. At the same time, another common condition called anemia, where the blood lacks enough healthy red cells to carry oxygen, also hits these same groups harder. While doctors know that the body reacts to anemia by working harder to move oxygen around, scientists have long been puzzled by how this struggle connects to blood pressure. Some studies suggest that having low iron raises pressure, while others find the opposite, leaving a confusing picture of whether these two conditions push each other up or pull in different directions.

A team of researchers from the University of Alabama decided to look closely at this puzzle within a specific community: the rural counties of West Alabama, a region known for its rich soil but also for deep health disparities. They gathered medical records from over 1,200 adults who had visited local clinics, looking at their blood pressure readings alongside their anemia status, race, and gender. Instead of simply averaging the results for everyone, they asked a more specific question: does the link between anemia and blood pressure change depending on who you are? They wanted to see if the relationship looked different for a Black man compared to a White man, or for a woman compared to a man.

What they found was that the connection is not a single, straight line but a complex web that shifts based on demographics. The study revealed that for men, race made a dramatic difference in how anemia affected their blood pressure. Among Black men, those with anemia had significantly higher blood pressure than those without it; their systolic pressure, the top number in a reading, was about 8.4 points higher, and their diastolic pressure, the bottom number, was nearly 5 points higher. In stark contrast, among White men, having anemia was actually associated with slightly lower blood pressure. This reversal meant that the same condition pushed pressure up for one group of men while pulling it down for another.

The story was different for women. While Black women in the study did have higher blood pressure overall and a higher rate of anemia than White women, the presence of anemia did not create a noticeable difference in their blood pressure readings regardless of their race. The researchers noted that the complex interactions they observed were driven almost entirely by the differences seen in men. This suggests that the factors influencing blood pressure in the presence of anemia are not uniform; they are shaped by a mix of biology, environment, and social experience that varies between groups.

The authors are careful to explain that race itself is not the biological cause of these differences. Instead, they view race as a marker for a collection of other realities, such as exposure to chronic stress, access to healthcare, diet, and environmental conditions, all of which can alter how the body responds to low oxygen. Because the study looked at a single snapshot in time rather than following people over years, it cannot prove that anemia causes the blood pressure changes or vice versa. However, the findings strongly suggest that treating high blood pressure or anemia requires a more tailored approach. A one-size-fits-all understanding of how these conditions interact may hide the specific risks faced by different groups, particularly Black men in rural settings, and future research needs to dig deeper into the specific social and biological factors that create these distinct patterns.

Technical Summary: Heterogeneity in the Association Between Anemia and Blood Pressure in a Rural Population

Problem Statement
The relationship between anemia and blood pressure remains incompletely understood, with prior literature reporting inconsistent findings ranging from inverse associations to positive correlations. While both conditions disproportionately affect specific demographic groups—particularly African American adults and women in the United States, and rural populations generally—the extent to which the association between anemia and blood pressure varies across these groups is unclear. Existing studies often fail to account for effect modification by race and gender, potentially obscuring clinically meaningful differences in how these conditions interact within specific subpopulations. This study addresses the need to examine whether the association between anemia and blood pressure differs across demographic groups in a rural setting where both hypertension and anemia are highly prevalent.

Methodology

Study Design and Data Source: This retrospective study analyzed clinical data from the Alabama State Health Information Exchange (HIE) covering West Alabama counties. The data collection period was from February 4, 2026, to March 19, 2026.
Sample: The analytic sample consisted of 1,212 adult participants (579 African American, 633 White; 332 men, 880 women) with available demographic information and clinical measures, including blood pressure and anemia indicators (hemoglobin, hematocrit, or red blood cell count).
Statistical Analysis: General Linear Models (GLMs) were employed to examine independent and interactive effects of race, gender, age, and anemia status on systolic and diastolic blood pressure. The models included two-way interactions (race × anemia, gender × anemia, age × anemia) and a three-way interaction (race × gender × anemia). Significant interactions were further explored using sex-stratified models and least squares mean comparisons. Analyses were conducted using SAS 9.4 with a significance level of $\alpha = 0.05$ .
Definitions: Anemia was defined based on clinical thresholds for hemoglobin, hematocrit, and red blood cell count.

Key Contributions
The primary contribution of this work is the empirical demonstration that the association between anemia and blood pressure is not uniform but is heterogeneous across demographic groups. By utilizing interaction terms in multivariable models, the study moves beyond main-effect analyses to reveal that race and gender significantly modify the relationship between anemia and blood pressure. Specifically, the study identifies that these interactions are driven primarily by gender differences, with distinct patterns observed in men compared to women.

Results

Systolic Blood Pressure (SBP): Significant main effects were found for age, race, and gender. Crucially, significant interactions were observed for race × anemia and the three-way race × gender × anemia.
- Men: A stark contrast was observed. Among African American men, anemia was associated with an 8.4 mmHg higher adjusted SBP compared to non-anemic African American men. Conversely, among White men, anemia was associated with a 7.2 mmHg lower adjusted SBP.
- Women: No significant race × anemia interaction was observed. Differences associated with anemia were minimal for both African American women (+1.7 mmHg) and White women (+0.6 mmHg).
Diastolic Blood Pressure (DBP): Similar patterns emerged. Race was a significant predictor, and significant race × anemia and race × gender × anemia interactions were detected.
- Men: African American men with anemia had a 4.9 mmHg higher adjusted DBP than their non-anemic counterparts. In contrast, anemia was associated with lower adjusted DBP in White men and White women.
- Women: No race × anemia interaction was found for DBP.
Gender Stratification: When models were stratified by gender, the three-way interaction was driven entirely by men. Significant race × anemia interactions were found for both SBP and DBP in men, whereas no such interactions existed for women.

Significance and Claims
The authors conclude that the relationship between anemia and blood pressure is heterogeneous and that demographic variables (specifically race and gender) serve as markers for this heterogeneity. The paper explicitly states that race itself is not a causal biological determinant but rather a marker of underlying biological, clinical, environmental, and psychosocial exposures (e.g., structural racism, socioeconomic disadvantage, chronic stress, healthcare access) that influence cardiovascular risk.

The study emphasizes that averaging effects across heterogeneous populations may obscure clinically meaningful differences. The findings suggest that the mechanisms linking anemia and hypertension likely involve a complex interplay of physiological responses (e.g., cardiac output, blood viscosity) and broader social determinants of health. The authors caution that due to the cross-sectional design and lack of data on anemia etiology, kidney function, and specific social determinants, the study cannot establish causality or fully explain the mechanisms. Instead, the findings are presented as hypothesis-generating, highlighting the necessity for future research to directly measure the biological and social factors underlying these demographic differences to better understand hypertension risk and inform precision medicine approaches.

Technical Summary: Heterogeneity in the Association Between Anemia and Blood Pressure in a Rural Population

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