Health Literacy and 1-Year Mortality: Mechanisms of Association in Adults Hospitalized for Cardiovascular Disease

Abstract

Objective: To test theorized patient-level mediators in the causal pathway between health literacy (HL) and 1-year mortality in adults with cardiovascular disease (CVD).

Patients and methods: A total of 3000 adults treated at Vanderbilt University Hospital from October 11, 2011, through December 18, 2015, for acute coronary syndrome or acute decompensated heart failure (ADHF) participated in the Vanderbilt Inpatient Cohort Study. Participants completed a bedside-administered survey and consented to health record review and longitudinal follow-up. Multivariable mediation models examined the direct and indirect effects of HL (a latent variable with 4 indicators) with 1-year mortality after discharge (dichotomous). Hypothesized mediators included social support, health competence, health behavior, comorbidity index, type of CVD diagnosis, and previous-year hospitalizations.

Results: Of the 2977 patients discharged from the hospital (60% male; mean age, 61 years; 83% non-Hispanic white, 37% admitted for ADHF), 17% to 23% had inadequate HL depending on the measure, and 10% (n=304) died within 1 year. The total effect of lower HL on 1-year mortality (adjusted odds ratio [AOR]=1.31; 95% CI, 1.01-1.69) was decomposed into an indirect effect (AOR=1.50; 95% CI, 1.35-1.67) via the mediators and a nonsignificant direct effect (AOR=0.87; 95% CI, 0.66-1.14). Each SD decrease in HL was associated with an absolute 3.2 percentage point increase in the probability of 1-year mortality via mediators admitted for ADHF, comorbidities, health behavior, health competence, and previous-year hospitalizations (listed by contribution to indirect effect).

Conclusion: Patient-level factors link low HL and mortality. Health competence and health behavior are modifiable mediators that could be targeted by interventions post hospitalization for CVD.

Figure 1.. Mediation models examining the relationship between lower health literacy (HL) and 1-year mortality.

A) Base model (no mediators); total effect (c) of lower HL on 1-year mortality adjusted for covariates. B) Multiple mediator model; decomposes total effect into a direct (c’) and total indirect (ab) effect. Direct effect (c’) depicts effect of lower HL on 1-year mortality adjusted for all covariates and mediators; a paths depict effects of lower HL on each mediator adjusted for other mediators and covariates; b paths depict effects of mediators on 1-year mortality adjusted for all other mediators, covariates, and HL. The Karlson, Holm, & Breen method used for analyses adjusts for other mediators when calculated separate effects of each (depicted with curved arrows). Covariates were age, gender, minority status, and socioeconomic status (not shown).

Figure 2.. Final measurement model used for latent variables used in mediation analyses.

The three latent variables used in mediation analyses were Health Literacy, Social Support, and Socioeconomic Status. The numbers (right to left) depict: correlations between the latent variables; standardized coefficients for the factor loading of each indicator (measure); correlations between the residual measurement error (e) for some indicators. BHLS = Brief Health Literacy Screen; ENRICHD = Enhancing Recovery in Coronary Heart Disease Social Support Inventory; SNS-3 = Subjective Numeracy Scale-3; S-TOFHLA = Short form of the Test of Functional Health Literacy in Adults.