Although low health literacy is now widely recognized to have a significant negative impact on both the individual and public health, tools to measure health literacy and strategies to improve care of the low literacy population have been developed only recently. For the third time in as many decades, the National Center for Education Statistics (2006) measured the English literacy of the U.S. population in the 2003 National Assessment of Adult Literacy. This survey was the first to include measurement of health literacy in addition to overall U.S. English literacy. The National Assessment of Adult Literacy surveyed a representative sample of 18,000 U.S. households as well as 1,200 persons in prisons. For the purpose of this study, health literacy was defined using the previously quoted IOM definition (National Center for Education Statistics, 2006).

Health literacy was measured using the three literacy measures used in the overall English literacy assessments by the 2003 National Assessment of Adult Literacy survey: prose, document, and quantitative measures. Prose literacy is defined as the ability to search, comprehend, and use information from continuous text. Document literacy is defined as the ability to search, comprehend, and use information from noncontinuous text (e.g., application forms or maps). Quantitative literacy is defined as the ability to identify and perform computation using numbers embedded in print materials (e.g., balancing a checkbook). In addition, three domains specific to health literacy were identified and measured: clinical, prevention, and navigation of the health system. The clinical domain was defined as the activities involved in the provider-patient interaction, such as completing forms and understanding medication dosages. The prevention domain was defined as activities related to disease prevention and self-management of illness. Navigation of the health system included activities such as understanding health insurance plans and consent forms.

Results of the 2003 adult health literacy survey showed that 36% of the U.S. population, or approximately 87 million adults, had either below basic (14%) or basic (22%) health literacy levels, defined as

Disparities among particular subpopulations were also noted. Hispanic populations had the lowest percentage of health literacy among ethnic groups. More men (16%) than women (12%) had below basic health literacy levels. Persons who did not speak English before attending primary school had lower health literacy than those who spoke English at early ages, and adults over age 65 had lower health literacy than other age groups. Educational attainment was significantly associated with below basic health literacy: 49% of individuals who did not complete either high school or a General Educational Development program had below basic health literacy scores. Adults living in poverty had lower health literacy levels than other socioeconomic groups, as did persons who had self-perceived overall health at lower ratings. Persons who had no health insurance or had Medicaid/Medicare had lower health literacy levels. Those who obtained their basic health information from television or radio had lower health literacy than those who obtained information from print media (National Center for Education Statistics, 2006).

Low health literacy may contribute significantly to the notable health disparities across specific populations in the United States. One of the overarching goals of Healthy People 2020 (U.S. DHHS, 2010c) is to reduce these health disparities, which lead to increased morbidity and mortality as well as inefficient and ineffective use of public resources. Estimates of the cost of low health literacy to U.S. society range from $106 to $236 billion annually (Vernon, Trujillo, Rosenbaum, & DeBuono, 2007). When future and indirect costs are accounted for, this estimate increases to a range from $1.6 to $3.6 trillion annually (Vernon et al., 2007). Clearly, low health literacy is a public health condition of great consequence.

Many studies have documented how low health literacy impacts a person’s ability to obtain preventive screening services and to manage one’s chronic diseases. Based on the level of evidence ratings in Box 5-1, the following evidence is reported. In a systematic review of the literature, Berkman, Sheridan, Donahue, Halpern, and Crotty (2011) found that patients with low health literacy used health resources less frequently than their higher literacy counterparts (level I). Maniaci, Heckman, and Dawson (2008) found that patients with lower levels of health literacy were found to have less medication knowledge after hospital discharge (level IV). In addition, patients with type 2 diabetes mellitus and low health literacy were found to have higher HgA_1C levels and higher rates of retinopathy than those with higher health literacy levels (Schillinger et al., 2002) (level IV). Patients with low health literacy were less likely to use preventive services (IOM, 2004) (level V). Also, higher mortality rates were associated with lower health literacy scores (Baker et al., 2007) (level IV). Patients with low health literacy have higher rates of hospitalizations and complications and higher emergency room use (Baker, Parker, Williams, & Clark, 1998; Baker et al., 2002) (level IV). Among elderly patients 65 and older, low health literacy was associated with increased hospitalizations, higher emergency room utilization, poor medication adherence, and impaired ability to interpret
health messages (Berkman, Sheridan, Donahue, Halpern, Viera, et al., 2011) (level I). Moreover, patients with low health literacy were two to three times more likely to experience poor outcomes (DeWalt, Berkman, Sheridan, Lohr & Pignone, 2004) (level I).