Health Literacy Mediates the Relationship Between Age and Health Outcomes in Patients With Heart Failure

Abstract

Background: Previous studies have linked frequent rehospitalizations for heart failure (HF) and increased mortality with older age, higher severity of HF, lack of an evidence-based medication regimen, and inadequate health literacy. However, the pathway between age and health outcomes in patients with HF remains unknown. Therefore, the purpose of this study was to test whether the association between age and health outcomes can be explained by severity of HF, evidence-based medication use, and health literacy in patients with HF.

Methods and results: This was a longitudinal study of 575 rural patients with HF recruited from outpatient clinics and hospitals. Demographics, clinical data, and health literacy were collected at baseline. HF readmissions and cardiac mortality were followed for 2 years; 57% of patients were ≥ 65 years of age. Older patients with HF were more likely to have low health literacy and less likely to be prescribed angiotensin-converting enzyme inhibitors or β-blockers. Using Kaplan-Meier survival curves with log-rank tests, health outcomes were significantly worse in patients who were ≥ 65 years and in those with low health literacy. Separate Cox regressions revealed that age and health literacy predicted worse health outcomes (P = 0.006 and < 0.001, respectively). When health literacy was entered into the model, the hazard ratio for age changed from 1.49 to 1.29 (a 41% reduction); age was no longer a significant predictor of health outcomes, but health literacy remained significant (P < 0.001), demonstrating mediation.

Conclusions: Health literacy mediates the relationship between age and health outcomes in adults with HF.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00415545.

Keywords: aging; angiotensin-converting enzyme inhibitors; health literacy; heart failure; longitudinal studies.

© 2015 American Heart Association, Inc.

Figures

Figure 1

Test of health literacy as a mediator of the relationship between age and cardiac-free survival; age and health literacy are included in the models as continuous variables. The results of the four regression models specified in Paths A–D demonstrate that health literacy completely mediates this relationship, as evidenced by a significant association between age and event-free survival until health literacy is added to the model.

Figure 2

Kaplan-Meier survival curves for patient age groups consisting of those less than 65 (blue line) versus 65 and above (red line); each censored observation appears as a plus. With 93% of the sample followed for 750 days or less, the Kaplan-Meier curves excluded those followed for a longer time; the number of patients at risk for each 200-day period is shown by age group at the base of the graph. The group comparison of event-free survival is significant (χ2 = 4.2; p = .04).

Figure 3

Test of health literacy as a mediator of the relationship between age and cardiac-free survival; age and health literacy are included in the models as dichotomous variables. The results of the four regression models specified in Paths A–D demonstrate that health literacy completely mediates this relationship, as evidenced by a significant association between age and event-free survival until health literacy is added to the model.