Poor Health Literacy in the Elderly Predicts All-Cause and Cardiovascular Mortality

July 31, 2007 — Elderly patients with poor health literacy have higher incidence of all-cause mortality and cardiovascular death, according to the results of a prospective cohort study published in the July 23 issue of Archives of Internal Medicine.
"Individuals with low levels of health literacy have less health knowledge, worse self-management of chronic disease, lower use of preventive services, and worse health in cross-sectional studies," write David W. Baker, MD, MPH, from the Feinberg School of Medicine at Northwestern University in Chicago, Illinois, and colleagues. "The number of years of school completed is strongly associated with reading fluency. As a result, individuals with more education tend to have a better capacity to obtain, process and understand basic health information and services needed to make appropriate health decisions: i.e., they have higher levels of health literacy."
The objective of this study was to determine whether low levels of health literacy were independent predictors of overall and cause-specific mortality.
In 4 US metropolitan areas in 1997, the investigators interviewed 3260 Medicare managed-care enrollees, aged 65 years or older, concerning their demographic characteristics, chronic health conditions, self-reported physical and mental health, and health behaviors. They also performed the shortened version of the Test of Functional Health Literacy in Adults that involved 2 reading passages and 4 mathematical questions.
Primary endpoints were deaths from all causes and from cardiovascular, cancer, and other causes, based on data through 2003 from the National Death Index.
During follow-up of 67.8 months' average duration, 815 (25%) participants died. For participants with adequate health literacy (n = 2094; 64.2%), the crude mortality rate was 18.9% compared with 28.7% in those with marginal health literacy (n = 366; 11.2%) and 39.4% in those with inadequate health literacy (n = 800; 24.5%; P < .001).
Compared with participants with adequate health literacy, hazard ratios for all-cause mortality were 1.52 for participants with inadequate health literacy (95% confidence interval, 1.26 - 1.83) and 1.13 for participants with marginal health literacy (95% confidence interval, 0.90 - 1.41), after adjustment for demographic factors, socioeconomic status, and baseline health.
In bivariate analyses, years of school completed was only weakly associated with mortality, and in multivariate models, years of school completed was not a significant predictor of mortality.
"Inadequate health literacy, as measured by reading fluency, independently predicts all-cause mortality and cardiovascular death among community-dwelling elderly persons," the authors write. "Reading fluency is a more powerful variable than education for examining the association between socioeconomic status and health."
Risk-adjusted rates of cardiovascular death, but not of cancer-related death, were higher in participants with inadequate health literacy. During the study, 380 (11.7%) of participants died of cardiovascular disease, including 19.3% of those with inadequate health literacy, 16.7% of those with marginal health literacy, and 7.9% of those with adequate health literacy.
Study limitations include possible unmeasured confounding variables, such as cognitive function.
Several mechanisms suggested by the authors to explain increased mortality in patients with inadequate health literacy include less knowledge regarding chronic disease; worse self-management skills for hypertension, diabetes, asthma, and heart failure; and lower use of cancer screening and vaccinations.
"Most people will have many acute and chronic medical conditions during their life and face many situations in which they must make health and health care choices and decisions," the authors conclude. "As a result of these myriad demands placed on patients today, widespread improvements in health and health care communication will likely be necessary to reduce the association between health literacy and mortality."
The National Institute on Aging and a Career Development Award from the Centers for Disease Control and Prevention supported this study. The authors have disclosed no relevant financial relationships.
Arch Intern Med. 2007;167:1503-1509.