Including literacy in predictive health status models removed the predictive power of both education and African-American race. This offers an insight into the mechanisms that might explain the influence of 2 of the most commonly documented sources of health disparities.
Although education is a well-established and commonly used predictor of health, the pathways and mechanisms that account for this association remain both empirically and theoretically unspecified.14
Education, as traditionally measured in health research, is simply a tally of years completed or degrees achieved within school systems that are not necessarily equivalent, by individuals who may not have gained or retained the same skills. This may be particularly true for the elderly who have not been in school in many years, but may continue to increase, or decrease, their literacy skills throughout their lives.15
Thus, the traditional education variable does not necessarily measure true “education” at all.3,4,16
Literacy, conversely, is conceived and measured as a set of functional skills that are relevant to the demands of everyday life11
and has been found to vary widely among individuals with the same educational attainment.11,17
As a direct measure of practical skills, only some of which are imparted through the formal educational system, literacy could impact health on a variety of levels from health care access to health knowledge accumulation to disease-specific management.18
If discrepancies between education and literacy occurred at random, the addition of adult literacy to predictive models of health might lessen education's association with health, but may not impact the relationship of race and health. However, the education/literacy discrepancy does not occur randomly. On average, African-American and Hispanic adults are more likely to have lower literacy when education is controlled.11
The lack of equivalency of skills by education level means that education, as traditionally measured, is not an adequate control for educational attainment. In predicting health status, adult literacy could reduce the predictive power of race, not because literacy is a better measure of the theoretical influence of this variable on health (as is the case with education), but because literacy is a more equivalent statistical control for educational attainment than traditional education variables. Undoubtedly, there are other reasons besides unequal literacy for race-based health inequalities. In this study, African-American race remained a significant predictor of health status among the sample of adults 65+, indicating that race and literacy had independent relationships with health.
As the NALS was not a health survey by design, the health status measures were not standard. The relationship of literacy, education, and race with health should be tested using more traditional measures of health status and disease-specific outcomes. National health surveys should include literacy evaluation to allow full exploration of these relationships.
Literacy in this study was only measured as English literacy. Some individuals, particularly recent immigrants, may have low English literacy skills, yet may be highly literate in other languages. Health care outreach, health measures, patient education, and doctor-patient care can be provided in other languages, although the availability of these services differs greatly across regions and health care facilities. Exploring the relationship of health and literacy in languages other than English is an important area for further study. This could also help us better understand the relationship between literacy, ethnicity, and health. In this study, no relationship was seen between Hispanic heritage and health, perhaps due to the peculiarities of this sample, cultural differences in responses concerning self-reported health,19
or the so-called “Hispanic paradox” wherein some Hispanic groups have better than expected health outcomes, despite greater socioeconomic disadvantage.20
The data analyzed are somewhat outdated as the NALS is from 1992. Important changes in health care delivery, such as the growth of managed care, more complicated protocols for seeing a specialist, and advances in technology leading to more complicated clinical regimens, have occurred in the last decade. As these changes have made the health care system even more complex, these could increase the impact that functional skills might have on health. However, literacy has started to gain recognition as an important issue in health care and some effort has been made to improve the literacy demands of patient education and other health-related materials. This may actually decrease the relationship of literacy with health. The 2003 National Assessment of Adult Literacy (NAAL), a follow-up to the NALS, included more specific health status and health use questions.21
Replicating the analyses reported here with these soon-to-be-released data should provide more definitive information about the relationship of literacy, education, race, and health status. Also, while the NALS only measured general literacy, the NAAL measured both general and health literacy. A consideration of the NAAL data will allow practical comparisons of a general functional literacy measure compared with a health literacy assessment, in general, and specifically in relationship with health.
This study provides some illumination into a possible causal pathway of health disparities. Literacy was significantly associated with both health status measures. Although the OR for literacy (0.90 and 0.96) may at first appear small, each point-increase in the literacy variable represents a 10-point increment on a 500-point scale. Across large differences in literacy skill, the cumulative effects of each 10-point difference result in very different probabilities of having a work-impairing condition or a long-term illness. However, this study did not specifically test for causality. We cannot rule out the possibility that literacy may not be a direct measure of skills relevant to health, but rather a better proxy than education and race for other crucial, unmeasured aspects of socioeconomic status, such as discrimination or adverse opportunity structures, that are the actual causal factors. Further research into possible causal pathways exploring the health literacy relationship will help illuminate these issues.
This study has important implications for the large, well-established field of research into health disparities and the social determinants of health. When literacy was considered in a nationally representative sample of noninstitutionalized adults, as well as separately among younger (<65) and older (65+) adults, education and race ceased to maintain their traditional importance for understanding health disparities. This suggests that literacy may be an important predictor of health disparities that explains differences by race and education observed in previous studies. Literacy may also provide a particularly effective area to focus the fight to eliminate health disparities as adult literacy can be potentially improved across the lifespan, and the literacy-related demands of the health care system can be directly targeted by both large-scale policy and individual clinical action.