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- Title
Behavioral risk factors and socioeconomic inequalities in ischemic heart disease mortality in the United States: A causal mediation analysis using record linkage data.
- Authors
Zhu, Yachen; Llamosas-Falcón, Laura; Kerr, William C.; Rehm, Jürgen; Probst, Charlotte
- Abstract
Background: Ischemic heart disease (IHD) is a major cause of death in the United States (US), with marked mortality inequalities. Previous studies have reported inconsistent findings regarding the contributions of behavioral risk factors (BRFs) to socioeconomic inequalities in IHD mortality. To our knowledge, no nationwide study has been conducted on this topic in the US. Methods and findings: In this cohort study, we obtained data from the 1997 to 2018 National Health Interview Survey with mortality follow-up until December 31, 2019 from the National Death Index. A total of 524,035 people aged 25 years and older were followed up for 10.3 years on average (SD: 6.1 years), during which 13,256 IHD deaths occurred. Counterfactual-based causal mediation analyses with Cox proportional hazards models were performed to quantify the contributions of 4 BRFs (smoking, alcohol use, physical inactivity, and BMI) to socioeconomic inequalities in IHD mortality. Education was used as the primary indicator for socioeconomic status (SES). Analyses were performed stratified by sex and adjusted for marital status, race and ethnicity, and survey year. In both males and females, clear socioeconomic gradients in IHD mortality were observed, with low- and middle-education people bearing statistically significantly higher risks compared to high-education people. We found statistically significant natural direct effects of SES (HR = 1.16, 95% CI: 1.06, 1.27 in males; HR = 1.28, 95% CI: 1.10, 1.49 in females) on IHD mortality and natural indirect effects through the causal pathways of smoking (HR = 1.18, 95% CI: 1.15, 1.20 in males; HR = 1.11, 95% CI: 1.08, 1.13 in females), physical inactivity (HR = 1.16, 95% CI: 1.14, 1.19 in males; HR = 1.18, 95% CI: 1.15, 1.20 in females), alcohol use (HR = 1.07, 95% CI: 1.06, 1.09 in males; HR = 1.09, 95% CI: 1.08, 1.11 in females), and BMI (HR = 1.03, 95% CI: 1.02, 1.04 in males; HR = 1.03, 95% CI: 1.02, 1.04 in females). Smoking, physical inactivity, alcohol use, and BMI mediated 29% (95% CI, 24%, 35%), 27% (95% CI, 22%, 33%), 12% (95% CI, 10%, 16%), and 5% (95% CI, 4%, 7%) of the inequalities in IHD mortality between low- and high-education males, respectively; the corresponding proportions mediated were 16% (95% CI, 11%, 23%), 26% (95% CI, 20%, 34%), 14% (95% CI, 11%, 19%), and 5% (95% CI, 3%, 7%) in females. Proportions mediated were slightly lower with family income used as the secondary indicator for SES. The main limitation of the methodology is that we could not rule out residual exposure-mediator, exposure-outcome, and mediator-outcome confounding. Conclusions: In this study, BRFs explained more than half of the educational differences in IHD mortality, with some variations by sex. Public health interventions to reduce intermediate risk factors are crucial to reduce the socioeconomic disparities and burden of IHD mortality in the general US population. Yachen Zhu and colleagues leverage data from linked records in the United States and apply causal inference methods to explore how behavioral factors and socioeconomics impact ischaemic heart disease related mortality. Author summary: Why was this study done?: Ischemic heart disease (IHD) is a major cause of death in the United States (US) and worldwide, with high mortality inequalities. Conflicting evidence for the contributions of behavioral risk factors (BRFs) to socioeconomic inequalities in IHD mortality exists within international literature, in part because a variety of methodological approaches have been used to answer the question. We used a novel counterfactual-based causal mediation method to explore the extent to which smoking, alcohol use, physical inactivity, and BMI explained the socioeconomic inequalities in US IHD mortality. What did the researchers do and find?: We obtained data for demographics and health behaviors of 524,025 participants from the 1997 to 2018 US National Health Interview Survey and linked to mortality data from the 2019 National Death Index. We used education as the primary indicator for socioeconomic status (SES). We found a clear impact of SES on IHD mortality, with variations by sex. Smoking, physical inactivity, alcohol use, and BMI together explained 74% of the inequalities between low- and high-education groups in males and 61% of the inequalities in females. BRFs also explained more than half of the inequalities between middle- and high-education people in both sexes. What do these findings mean?: Socioeconomic inequality significantly influences the burden of IHD mortality in the general US population. Public health interventions to target at BRFs are crucial to reducing this disparity. The findings are subject to measurement errors as they are based on single, self-reported assessments of the BRFs as well as residual confounding due to unobserved or unknown confounders such as genetic factors that are not accounted for.
- Publication
PLoS Medicine, 2024, Vol 21, Issue 9, p1
- ISSN
1549-1277
- Publication type
Article
- DOI
10.1371/journal.pmed.1004455