Contribution of Four Comorbid Conditions to Racial/Ethnic Disparities in Mortality Risk

doi:10.1016/j.amepre.2016.07.036

American Journal of Preventive Medicine

Volume 52, Issue 1, Supplement 1, January 2017, Pages S95-S102

https://doi.org/10.1016/j.amepre.2016.07.036 Get rights and content

Introduction

The prevalence of key forms of morbidity such as obesity, diabetes, and chronic kidney disease have increased dramatically in the U.S. and elsewhere for decades. Hypertension is etiologically related but its prevalence has been reduced through improved treatment. These diseases are known to have higher than expected rates of comorbidity, but it is not known whether and how these cluster together differentially by race, nor the degree to which they contribute to racial disparities in mortality.

Methods

Using data from the National Health Interview Survey mortality follow-up (1997–2009, analyzed in 2016), this paper modeled interdependencies between each combination of these four types of morbidity, overall and net of demographic, socioeconomic, and behavioral controls. It then analyzed whether these diseases mediate the relationship between race/ethnicity and mortality risk using discrete time complementary log–log survival models.

Results

American Indians and blacks had significantly elevated rates of comorbidity compared with whites, and Asians’ and Pacific Islanders’ rates were often significantly lower than whites’. Controlling for these diseases significantly moderated the mortality risk disparity between African American, Hispanic, and Asian/Pacific Islanders and whites. This remained true when individual health behaviors and neighborhood fixed effects were statistically adjusted for. Notably, the full controls model statistically eliminated the association between African American race and mortality risk.

Conclusions

These diseases contribute significantly to racial/ethnic mortality disparities, particularly between blacks and whites. Future research should consider the mediating role of these diseases for the relationship between social conditions and mortality risks.

Introduction

The epidemiologic transition describes the shift from mortality and morbidity dominated by infectious diseases to mortality and morbidity primarily caused by chronic diseases and their precursors. Four forms of morbidity are especially critical and inter-related: obesity (OB), diabetes mellitus (DM), hypertension (HT), and chronic kidney disease (CKD). The prevalence of OB (defined as BMI ≥30) increased by 8 percentage points between 1980 and 1994, with a similar increase from 1994 to 1999, with continued, demographic-specific increases in the 2000s.¹ Similarly, the prevalence of DM (defined as hemoglobin A1c ≥6.5%) has increased from 5.8% in 1988–1994 to 12.4% in 2005–2010.² Smaller increases in the prevalence of CKD have been observed, as the percentage with CKD (measured as estimated glomerular filtration rate <60 or albumin to creatinine ratio ≥30) increased from 12.3% to 14.0%.³ However, hypertension prevalence trends have gone against the patterns of these other diseases, as improved treatment regimens reduced the prevalence between 1960 and 1990, remaining approximately flat in the decades since.4, 5 The changing prevalence of these diseases is likely to have long-lasting repercussions on the health and longevity of the U.S. population and those of other developed and developing countries for decades to come.

These rising morbidity prevalences are not independent—having one of each of these diseases is predictive of having each of the others.6, 7, 8, 9 This is due to a combination of these diseases being subject to common environmental influences as well as one disease directly raising the hazard of developing others. For example, risk of obesity and CKD are both influenced by risk factors such as poor health behaviors, but being obese also directly impacts the risk of developing CKD.⁷ Health behaviors are a critical link in the association of these diseases with each other as well as social position—cigarette smoking, high alcohol consumption, poor diet, and low levels of physical activity are associated with increased risk of all four conditions. Therefore, social environments that promote these poor health behaviors will often show evidence of high rates of all four conditions. Accordingly, controlling for individual health behaviors is essential when studying the link between these diseases and mortality risk. Furthermore, in light of recent research showing the strong influence that places of residence can play in each of these outcomes,10, 11, 12, 13 estimating neighborhood effects, and their consequences for racial/ethnic mortality disparities, is a critical step to identify social environmental influences on morbidity and mortality outcomes.

This rising morbidity burden is also unequally distributed by race/ethnicity. The prevalence of these forms of morbidity is much higher in African American and Native American populations than it is in white and Asian American populations.1, 3, 14, 15 The differential prevalence of these sources of morbidity and their association with mortality risk also makes them candidate contributors to racial/ethnic mortality disparities.

Because these diseases do not arise in isolation from one another, it is critical to study their determinants and consequences for racial/ethnic mortality disparities jointly. This is especially important in the aftermath of the epidemiologic transition, which has the result that mortality typically follows long struggles with chronic forms of morbidity rather than acute infections or accidental or violent deaths. Because the prevalences of these diseases vary so sharply by race/ethnicity, it is also critical to examine the consequences of health behaviors that vary by race and the effects of social environments such as neighborhoods on both morbidity and mortality outcomes.

Figure 1 illustrates the approach of this paper to racial/ethnic disparities in mortality risk. Race/ethnicity is associated with risk of different forms of morbidity, which mediates the race–mortality risk association, which may also be modified by racial/ethnic patterns of health behaviors and neighborhood factors. Thus, the objective of this paper is to analyze patterns of comorbidities across racial/ethnic groups in the U.S. and their contribution to racial/ethnic disparities in mortality hazards. This paper tests two hypotheses:

1
There are racial disparities in the prevalence of these conditions, individually and in combination.
2
Clusters of these conditions partially and robustly mediate racial/ethnic disparities in mortality hazards.

Although previous research has extensively examined racial/ethnic disparities in morbidity and mortality, it is less common to combine them, and never have these forms of morbidity been modeled interactively as mediators of the race/ethnicity–mortality relationship.

Section snippets

Methods

This study used data from the National Health Interview Survey (NHIS), as harmonized in the Integrated Health Interview Series (IHIS),¹⁶ including years when mortality follow-up data (National Death Index [NDI], match runs) and key variables for the analysis were included—1997–2009. Statistical analyses were begun in 2015 and completed in 2016. The NHIS employs a repeated cross-section interview design using a multistage sampling procedure, which samples initially from 428 primary sampling

Results

Table 1 describes the key characteristics of the analytic data set for this paper. Means and proportions are weighted, whereas SDs and ranges are not. By 2011, 9.6% of this sample was confirmed dead, with about 1.3% dying per year of follow-up. Among those who died, the average years to death from interview was 5.16. Of this sample, 21% were obese, 8.4% had DM, 27.5% had hypertension, and 1.7% had CKD.

Table 2 demonstrates descriptively that different combinations of these diseases are strongly

Discussion

Research in the sociology of health and illness has long paid relatively little heed to specific diseases and forms of morbidity, thereby ignoring the potential influence of social processes on disease onset and progression or their contribution to disparities in mortality risk between social groups.²⁸ Accordingly, little previous research has examined how morbidity mediates the relationship between social groups such as race/ethnicity and mortality risk. This paper seeks to advance the

Conclusions

Along with combinations of morbid conditions, individual- and neighborhood-level influences play a critical role in contributing to racial/ethnic disparities in mortality risk—so much so, that the three combined statistically eliminate the association between African American and AIAN race/ethnicity and mortality hazards. Because these two groups have the highest mortality hazards of all racial/ethnic groups in the U.S., this finding is critical to understand disparities in mortality risk. This

Acknowledgments

Publication of this article was supported by the National Institutes of Health. The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the National Institutes of Health.

The author thanks Chenoia Bryant for her able research assistance, and the comments of the special issue editors for improving the quality of the manuscript and analysis. Publication of this article was supported by the National Institute on Minority Health

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: This article is part of a supplement issue titled Social Determinants of Health: An Approach to Health Disparities Research.

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Research articleContribution of Four Comorbid Conditions to Racial/Ethnic Disparities in Mortality Risk

Introduction

Methods

Results

Conclusions

Introduction

Section snippets

Methods

Results

Discussion

Conclusions

Acknowledgments

J Am Coll Cardiol

Am J Clin Nutr

Kidney Int

Lancet

Soc Sci Med

Soc Sci Med

Res Soc Stratif Mobil

Prevalence of obesity and trends in the distribution of body mass index among U.S. adults, 1999-2010

JAMA

Trends in prevalence and control of diabetes in the United States, 1988–1994 and 1999–2010

Ann Intern Med

USRDS 2013 Annual Data Report: Atlas of Chronic Kidney Disease and End-Stage Renal Disease in the United States

Trends in the prevalence, awareness, treatment, and control of hypertension in the adult U.S. population data from the health examination surveys, 1960 to 1991

Hypertension

Chronic kidney disease and mortality risk: a systematic review

J Am Soc Nephrol

Neighborhood risk factors for obesity

Obesity

Neighborhoods, obesity, and diabetes—a randomized social experiment

N Engl J Med

Research article
Contribution of Four Comorbid Conditions to Racial/Ethnic Disparities in Mortality Risk