Lee et al. BMC Public Health 2010, 10:614 http://www.biomedcentral.com/1471-2458/10/614 36% of American adults surveyed in the 2003 National Assessment of Adult Literacy (NAAL) had below basic (can perform simple everyday literacy activities) and basic health literacy (can perform no more than the most simple and concrete literacy activities) [23]; and 11.4% and 15.5% of adults in the U.K. and Japan, respec- tively, were considered to have low health literacy in national surveys [13,24]. However, this comparison is imprecise, because no similar tests have been developed to allow for international comparison. For example, instead of using a scale, the Japanese survey measured health literacy based on a single-item screening ques- tion, “How confident are you filling out forms by your- self?,” possibly under-estimating the percentage of adults with low health literacy. Similar to findings in the NAAL [21] and previous health literacy studies [4,13,23,25-28], older age, poorer educational attainment, and lower income were found to be associated with lower levels of health literacy in Taiwan. Furthermore, Taiwanese adults living in less populated and more rural areas tended to have a lower level of health literacy than adults living in more popu- lated and more urban areas. Taken together, these find- ings suggest low health literacy is not only a personal limitation but also an indication of disadvantaged social status. Contrary to our expectation, health literacy was not associated with self-rated physical health after controlling for age, gender, educational attainment, household income, and residential location. Although inadequate health literacy was significantly correlated with poor self- rated mental health, the association between health lit- eracy and self-rated mental health was limited in the multinomial logit model. These findings are surprising because most studies have shown a significant relation- ship between health literacy and self-rated health status [25,26,29-31]. One possible explanation for the difference is that previous studies were conducted primarily on patients recruited from clinics or older adults enrolled in a managed care plan; these patients may in general have poorer health than the general adult population. Alterna- tively, the limited contribution of health literacy to health status, over and beyond that of educational attainment, may be due to a high correspondence between health lit- eracy and educational attainment in Taiwanese adults. If this is true, educational attainment would be a sufficient indicator of health literacy skills among Taiwanese adults and health literacy assessment would have limited value. Furthermore, a focus on reducing educational disparities in health may help to decrease the health burden of poor health literacy as well. Also interesting was our findings that health literacy was not independently associated with health care utili- zation among Taiwanese adults. Current evidence on Page 6 of 8 health literacy as a predictor for health care utilization is decidedly mixed. Baker and colleagues found that patients in outpatient clinics who had inadequate health literacy were more likely to have physician visits and be hospitalized [14,29], while other studies did not find health literacy to be associated with physician visits, use of ER, or hospitalization [4,32]. Based on our step-wise analysis results that age, educational attainment and household income jointly explained the associations between health literacy and health care utilization, we suspect that the inconsistencies observed in existing lit- erature may result from inadequate consideration of socio-demographic factors. Alternatively, the finding of no association between health literacy and health care utilization may be due to the fact that needed health care is affordable and accessible to around 98% of the population in Taiwan. Several study limitations are worth noting. The limita- tions also point to opportunities for future research. First, only self-rated measures of health status and health care utilization were examined in the study. The reliabil- ity of self-rated health care utilization, in particular, may be subject to recall bias or memory failure. Linking health literacy test results to medical claims data would provide a more reliable assessment of the consequences of low health literacy. Second, results reported in the study were obtained from a cross-sectional survey and no causality is established between health literacy and health status and health care utilization. A longitudinal study that follows the study sample and reassesses their health outcomes at a later time would help to discern the causal effects of health literacy. Third, the MHLS, similar to other health literacy assessments, is primarily a reading and compre- hension test. It offers no indication about the respon- dent’s communication skills, which may be equally important in determining an individual’s ability to effec- tively navigate today’s complex health care system. Fourth, a significant proportion of the sample was miss- ing household income information. This may introduce systematic bias in the multinomial logit models. Although a separate analysis was conducted to assess the bias using imputed household income, the results should be interpreted with caution. Finally, we did not examine the associations of health literacy with disease knowledge, self-care skills, and health behaviors. To the extent that disease knowledge, self-care skills and health behaviors are important determinants for health, examining their associations with health literacy may help to devise inter- ventions to improve the health of disadvantaged sub- groups of the population. Conclusions From our study it is evident that low health literacy is widespread even in countries such as Taiwan that have