Skip to main content
NCBI home page
PLOS One logoLink to PLOS One
. 2024 Apr 18;19(4):e0301894. doi: 10.1371/journal.pone.0301894

Relationship between health literacy and health-related quality of life in Korean adults with chronic diseases

Inmyung Song 1,*
Editor: Uwe Konerding2
PMCID: PMC11025905  PMID: 38635779

Abstract

Inadequate health literacy is a risk factor for poor health outcomes and health-related quality of life (HRQoL). So far, the impact of health literacy on HRQoL has been examined for only a few chronic conditions. In this contribution, the relationship between health literacy and HRQoL in Korean adults with chronic conditions is examined using data of the cross-sectional Korea Health Panel Survey from 2021. Health literacy was measured with the 16-item European Health Literacy Survey Questionnaire (HLS-EU-Q16) and HRQoL with the European Quality of Life-5 Dimensions (EQ-5D). Multiple linear regression model was run for the EQ-5D index as the dependent variable. Multiple logistic regression models were implemented for responses to the individual EQ-5D items. 30.8%, 24.6%, and 44.6% of participants had inadequate, marginal, and adequate levels of health literacy, respectively. The EQ-5D index increases with marginal (B = 0.018, p<0.001) and adequate literacy (B = 0.017, p<0.001) compared to inadequate literacy. People with adequate or marginal literacy were more likely to report no problem with mobility (odds ration [OR] = 1.5; p<0.001), self-care (OR = 1.6; p<0.05), and usual activities (OR = 1.6 for adequate; OR = 1.4 for marginal; p<0.01) than those with inadequate literacy. Adequate health literacy was associated with an increased likelihood of having no problem with anxiety and depression (OR = 1.4; p<0.05). In conclusion, inadequate health literacy is prevalent among Korean adults with chronic diseases. Adequate health literacy is associated with better HRQoL and a protective factor for four dimensions of EQ-5D (mobility, self-care, usual activities, and anxiety/depression).

Introduction

There is a growing interest in health literacy and its impact on health outcomes [1,2]. Health literacy has been defined as “the degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions [3].” Over time, the complex construct of health literacy has evolved to represent “the knowledge, motivation and competencies of accessing, understanding, appraising and applying health-related information” in three domains of health care, disease prevention, and health promotion [4]. However, this critical “capacity” seems to be lacking in a large proportion of the population across countries [5]. According to a systematic review [6], nearly a half of adults in the U.S. have limited health literacy. A third of older adults in England have low functional health literacy, which means that they have difficulties reading and understanding basic written health information [7]. In Korea, nearly one in two adults aged 19 years and over have limited health literacy [8]. This is concerning, provided that Korea is an economically developed country with universal health coverage [9]. Korea is also known as one of highest-achieving countries with respect to scientific literacy [10], but its education is heavily reliant on exam-based education system [11], suggesting health literacy deserves assessment on its own.

Health literacy has been measured with a number of tools including the Rapid Estimate of Adult Literacy in Medicine (REALM) [12], the Test of Functional Health Literacy in Adults (TOFHLA) [6,13], the Newest Vital Sign (NVS) [14], and the Fostering Literacy for Good Health Today (FLIGHT) [15]. One of the newer measures was the European Health Literacy Survey Questionnaire (HLS-EU-Q). HLS-EU-Q was originally developed to measure health literacy in the European population [5], and was translated and used in a number of non-European populations [16]. The original version consisting of 47 items was designed to comprehensively assesses multiple conceptual domains of health literacy in diverse contexts [5], and later was shortened to a 16-item European Health Literacy Survey Questionnaire (HLS-EU-Q16). The efforts to measure health literacy across countries are underway, one example of which is the Health Literacy Study-Asia (HLS-Asia), which is a project organized with a view to provide an overview of the health literacy status in Asia [17].

Limited health literacy is linked to lower use of preventive care [18], greater use of emergency services [12], higher hospitalization rates [19], poorer health outcomes [1,2], and increased mortality [7,20]. As a result, limited health literacy increases economic burden on the health care system as well as on affected individuals [21]. Inadequate health literacy can be particularly problematic for patients with chronic conditions, because taking an active role in their own care is an important component of effective treatment. There is growing evidence that inadequate health literacy is associated with various health outcomes among patients with chronic conditions [22–24]. For example, low health literacy and self-care skills can negatively affect clinical outcomes among patients with cardiovascular disease and diabetes [22]. Low health literacy was associated with poorer control of blood pressure among patients with hypertension [23]. Furthermore, limited health literacy had a negative impact on patient-reported outcomes even after controlling for physician-rated disease activity among patients with systematic lupus erythematosus [24].

Reflecting the subjective experience of the patient, health-related quality of life (HRQoL) is an important patient-reported health outcome in patients with chronic conditions [25,26]. While chronic conditions have a negative impact on HRQoL [27], the adverse impact can be moderated by health literacy because it can improve self-care and self-management [28]. Health literacy is positively associated with HRQoL, measured with the European Quality of Life-5 Dimensions (EQ-5D) index, among spine patients recruited from a single medical center [14]. A chronic condition that garnered particular attention in relation to health literacy is type 2 diabetes [29–31]. Type 2 diabetes patients with adequate health literacy are less likely to experience a decline in EQ-5D over one year than those with low health literacy [30]. While these existing studies offer valuable insights regarding the role of adequate health literacy in HRQoL of patients with chronic disease, they are focused on a specific chronic condition [14,29,30], or based on a small sample of patients from a single [14] and few centers [29,31]. Moreover, the impacts of health literacy on specific dimensions of HRQoL are not fully understood [14].

Therefore, this study aims to evaluate the impact of health literacy on HRQoL among community-dwelling Korean adults with chronic conditions and to determine whether adequate health literacy is associated with increased likelihood of experiencing no problem with each dimension of HRQoL. The following hypotheses were formulated;

  1. Health literacy is positively associated with HRQoL in patients with chronic conditions.

  2. Health literacy has a differential impact across dimensions of HRQoL.

Methods

Data and the study population

This cross-sectional study used data from the Korea Health Panel Survey (KHPS) conducted in a nationally representative large sample of the population between March and July, 2021. The KHPS is a population-based panel survey that started in 2008. The KHPS used a two-stage stratified cluster sampling design [32]. Stratifications were done twice, first based on a large administrative district (city or province) and then on a smaller district. Trained interviewers conducted computer-assisted personal interviews face-to-face at the home of participants using a structured questionnaire.

The 2021 KHPS collected data on health literacy and EQ-5D among adults aged 19 years and older [8]. The KHPS also elicited information on chronic conditions, which included hypertension, diabetes mellitus, chronic hepatitis, alcoholic hepatitis, liver cirrhosis, osteoarthritis of the knee, degenerative arthritis of other joints, rheumatoid arthritis, spinal disc herniation, other spinal disease, stomach cancer, colon cancer, lung cancer, breast cancer, cervical cancer, thyroid cancer, other cancer, angina pectoris, myocardial infarction, cerebral infarction, asthma, emphysema, chronic obstructive pulmonary disease, bronchiectasis, hypothyroidism, hyperthyroidism, depression, dipolar disorder, dementia, chronic renal failure, and other chronic condition.

In the 2021 KHPS, 6,217 households were sampled and 6,190 (99.6%) participated in the survey [8]. A total of 13,530 members of the households responded to the survey. They were asked to indicate if they have any of the aforementioned chronic conditions diagnosed by a physician. In response, a total of 5,865 members reported that they had at least one chronic condition. Among them, 5,663 participants who answered health literacy questions were included for analysis.

Health literacy

HLS-EU-Q16 is a comprehensive measure of health literacy comprised of 16 questions in three domains: health care (7 items), disease prevention (5 items), and health promotion (4 items). Each item was rated on a 4-point Likert scale (very difficult, difficult, easy, and very easy). ‘Very difficult’ and ‘difficult’ were assigned 0, and ‘easy’ and ‘very easy’ 1. The scores on all items were summed. The summary scores were then classified into the following three levels of health literacy: inadequate (scores, 0–8), marginal (scores, 9–12), or adequate (scores, 13–16). HLS-EU-Q16 was translated into Korean using the translation and back-translation method [33]. Cronbach’s alpha for the Korean version is 0.861. The Korean version was used to assess health literacy in the 2021 KHPS. While the shorter 12-item European Health Literacy Survey Questionnaire (HLS-EU-Q12) was validated in other Asian countries at the time of the 2021 KHPS [34], the nationwide survey relied on the Korean version of the longer HLS-EU-Q16, which had been successfully used in the preceding years.

Health-related quality of life

HRQoL is a multidimensional construct consisting of physical, psychological, and social functioning dimensions [35]. The 2021 KHPS assessed HRQoL with EQ-5D. EQ-5D was initially developed as a concise measure of HRQoL that could be used across disease areas [36] and has been used to measure HRQoL in patients with chronic conditions [37]. The EQ-5D-3L is a preference-based index measure, based on five dimensions (mobility, self-care, usual activities, pain/discomfort, and anxiety/depression) with three levels of response (no problem, moderate problem, and severe problem). Each dimension of the EQ-5D is addressed by exactly one item. The instrument has been used widely in numerous nationwide surveys in Korea such as the KHPS [8]. Outcomes of interest in this current study were the EQ-5D index and responses to the individual EQ-5D items. The EQ-5D index was obtained using the EQ-5D value set derived from a representative sample of Korean adults [38]. For analysis of responses to the individual EQ-5D items, the three levels of response in each dimension were dichotomized into no problem and problem (inclusive of moderate to severe problems) categories.

Covariates

Potentially confounding factors for EQ-5D were identified and adjusted for in all regression models. Based on literature review, covariates included socio-demographic variables comprising sex, age, educational level, marital status, employment status, household income quartile and health-related variables such as disability, and multi-morbidity [25,39,40]. These variables could potentially influence EQ-5D and therefore were adjusted for in all regression models to better estimate the relationship between health literacy and EQ-5D. Educational level was classified as no or primary education, middle school, high school, and college and higher. Marital status was divided into currently married, formerly married (divorced/widowed/separated), and single. Employment status was divided into the employed, self-employed, and unemployed. Household income was divided into quartiles. Disability was divided into yes and no. Multi-morbidity was measured as the number of chronic conditions and divided into three categories (one, two, and ≥three conditions).

Statistical analysis

Sociodemographic and health-related characteristics of the participants were described with the frequency and percentage. The prevalence of health literacy levels across the categories of socio-demographic and health-related characteristics was calculated and the difference was tested by using Rao-Scott chi-square test, which is recommended for analyzing complex survey data [41]. The proportion of the participants reporting problems in EQ-5D dimensions was calculated and compared among health literacy levels. The mean EQ-5D index (±SE) was computed and the difference among health literacy levels was tested using the one-way analysis of variance. A multivariable linear regression model was run to examine if health literacy levels are associated with EQ-5D index. In addition, five multivariable logistic regression models were implemented to assess the relationship between health literacy levels and the likelihood of having no problem in each dimension of EQ-5D. For logistic regression analyses, adjusted odds ratio (OR) and 95% confidence intervals (CI) were calculated.

All statistical analyses were performed by using SAS version 9.4 (Cary, NC, USA). All analyses adjusted for sampling weights that were used in the complex sampling design of the 2021 KHPS. The complex survey uses oversampling of some subgroups of the population and poststratification adjustments for nonresponses, which cause the issues of unequal selection probability across subgroups and incorrect estimation of standard errors [42]. Sampling weights provided in complex survey data represent the inverse of selection probability. Units oversampled have a smaller weight value. Weighting was performed using the “surveyreg” and “surveylogistic” procedures in SAS. The Institutional Review Board of Kongju National University approved the study protocol and waived the requirement for informed consent (reference No. KNU_IRB_2023–101).

Results

In the weighted sample, 55.7% are women, 30.4% in their 60s, 66.6% currently married, and 43.8% unemployed (Table 1). 23.9% have a college-level education. 9.0% of participants have a disability and 22% three or more chronic conditions. 30.8%, 24.6%, and 44.6% have inadequate, marginal, and adequate levels of health literacy, respectively.

Table 1. Characteristics of study participants (n = 5,663).

Characteristic Category N % (weighted)
Gender male 2,400 44.3
female 3,263 55.7
Age, years 19–49 439 14.7
50–59 746 22.9
60–69 1,747 30.4
70–79 1,935 20.8
≥80 796 11.3
Educational level no or primary education 2,185 26.9
middle school 1,033 15.1
high school 1,595 34.1
college or higher 850 23.9
Marital status currently married 4,014 66.6
formerly married 1,467 27.5
single 182 5.9
Employment status employed 1,832 40.7
self-employed 975 15.5
unemployed 2,856 43.8
Household income quartile 1 (lowest) 1,413 22.0
2 1,414 18.7
3 1,414 22.9
4 (highest) 1,413 36.3
Disability yes 638 9.0
no 5,025 91.0
No. of chronic conditions 1 2,388 51.1
2 1,689 26.8
≥3 1,586 22.0
Health literacy level inadequate 2,276 30.8
marginal 1,445 24.6
  adequate 1,942 44.6
Open in a new tab

N is the frequency in the sample. % (weighted) is the population estimate.

The prevalence of health literacy levels varies significantly among the categories of all sociodemographic and health-related variables (p<0.001) (Table 2). In particular, adequate health literacy is more frequently observed in men, younger age groups, people with higher education, the single, the employed, higher income quartile, people with no disability, and people with fewer chronic conditions. The proportion of participants reporting problems in EQ-5D dimensions is highest for inadequate literacy and lowest for adequate literacy (Table 3). The mean EQ-5D index (± SE) is 0.864 (± 0.004) for inadequate, 0.917 (± 0.003) for marginal, and 0.944 (± 0.002) for adequate health literacy levels.

Table 2. Prevalence of health illiteracy levels by sociodemographic and health-related characteristics.

Characteristic Category Inadequate Marginal Adequate p-value
n % n % n %
Gender male 793 33.0% 621 25.9% 986 41.1% < .001
female 1,483 45.4% 824 25.3% 956 29.3%
Age, years 19–49 44 10.0% 80 18.2% 315 71.8% < .001
50–59 115 15.4% 168 22.5% 463 62.1%
60–69 496 28.4% 540 30.9% 711 40.7%
70–79 1,052 54.4% 500 25.8% 383 19.8%
≥80 569 71.5% 157 19.7% 70 8.8%
Educational level no or primary education 1,397 63.9% 528 24.2% 260 11.9% < .001
middle school 402 38.9% 326 31.6% 305 29.5%
high school 373 23.4% 434 27.2% 788 49.4%
college or higher 104 12.2% 157 18.5% 589 69.3%
Marital status currently married 1,418 35.3% 1,070 26.7% 1,526 38.0% < .001
formerly married 810 55.2% 346 23.6% 311 21.2%
single 48 26.4% 29 15.9% 105 57.7%
Employment status employed 534 29.1% 458 25.0% 840 45.9% < .001
self-employed 385 39.5% 243 24.9% 347 35.6%
unemployed 1,357 47.5% 744 26.1% 755 26.4%
Household income quartile 1 (lowest) 855 60.5% 317 22.4% 241 17.1% < .001
2 670 47.4% 385 27.2% 359 25.4%
3 451 31.9% 404 28.6% 559 39.5%
4 (highest) 294 20.8% 337 23.8% 782 55.3%
Disability yes 325 50.9% 177 27.7% 136 21.3% < .001
no 1,951 38.8% 1,268 25.2% 1,806 35.9%
No. of chronic conditions 1 671 28.1% 582 24.4% 1,135 47.5% < .001
2 706 41.8% 465 27.5% 518 30.7%
  ≥3 899 56.7% 398 25.1% 289 18.2%  
Open in a new tab

p-values were obtained by using the Rao-Scott chi-square test.

Table 3. Proportion of participants reporting problems in EQ-5D dimensions and mean EQ-5D index by health literacy levels.

  Inadequate (N = 2,264) Marginal (N = 1,437) Adequate (N = 1,940)  
EQ-5D dimension n % n % n % p-value
Mobility 999 44.1 339 23.6 254 13.1 < .001
Self-care 339 15.0 84 5.8 65 3.4 < .001
Usual activities 722 31.9 225 15.7 161 8.3 < .001
Pain/discomfort 1,378 60.9 712 49.5 708 36.5 < .001
Anxiety/depression 468 20.7 244 17.0 213 11.0 < .001
Mean EQ-5D index (± SE) 0.863 (± 0.004) 0.917 (± 0.003) 0.944 (± 0.002) < .001
Open in a new tab

p-values for EQ-5D dimensions were obtained by using the Rao-Scott chi-square test and the p-value for mean EQ-5D index by using the ANOVA.

The results of regression analysis show that EQ-5D index is positively associated with marginal (B = 0.018, p<0.001) and adequate health literacy levels (B = 0.017, p<0.001) compared to inadequate literacy (Table 4). The model accounts for 28.2% of variance in the EQ-5D index. Individuals with adequate literacy (OR = 1.5; 95% CI, 1.2–1.8; p<0.001) and those with marginal literacy (OR = 1.5; 95% CI, 1.2–2.0; p<0.001) are more likely to report no problem with mobility than those with inadequate literacy (Table 5). Adequate (OR = 1.6; 95% CI, 1.0–2.3; p<0.05) and marginal literacy (OR = 1.6; 95% CI, 1.1–2.2; p<0.05) increase the odds of having no problem with self-care. Individuals with adequate literacy (OR = 1.6; 95% CI, 1.2–2.2; p<0.01) and those with marginal literacy (OR = 1.4; 95% CI, 1.1–1.9; p<0.01) are more likely to report no problem with usual activities than those with inadequate literacy. Adequate health literacy is associated with an increased likelihood of reporting no problem with anxiety/depression (OR = 1.4; 95% CI, 1.1–1.9; p<0.05). Health literacy is not associated with the likelihood of having problems with pain and discomfort.

Table 4. Results of multiple regression analyses on EQ-5D index.

Characteristic (reference) Category Estimate SE p-value
Gender (female) male 0.009 0.003 < .01
Age (≥80), years 19–49 0.050 0.007 < .001
50–59 0.047 0.006 < .001
60–69 0.057 0.005 < .001
70–79 0.046 0.005 < .001
Education level (no or primary) middle school 0.015 0.004 < .001
high school 0.030 0.004 < .001
college or higher 0.036 0.005 < .001
Marital status (single) currently married 0.010 0.006 0.119
formerly married -0.002 0.007 0.800
Employment status (unemployed) employed 0.021 0.003 < .001
self-employed 0.027 0.004 < .001
Household income quartile (1) 2 0.012 0.004 < .01
3 0.022 0.005 < .001
4 (highest) 0.020 0.005 < .001
Disability (yes) no 0.071 0.005 < .001
No. of chronic conditions (≥3) 1 0.052 0.004 < .001
2 0.032 0.004 < .001
Health literacy (inadequate) marginal 0.018 0.004 < .001
adequate 0.017 0.004 < .001
Constant 0.698 0.009 < .001
No. of observations 5,632
R-square     0.282  
Open in a new tab

Table 5. Results of logistic regression analyses for the five dimensions of EQ-5D.

Characteristic (reference) Category Mobility Self-care Usual activities Pain/discomfort Anxiety/depression
OR 95% CI p OR 95% CI p OR 95% CI p OR 95% CI p OR 95% CI p
Gender (female) male 1.2 1.0 1.5 0.051 0.6 0.5 0.9 < .01 1.1 0.9 1.6 0.34 1.6 1.4 2.0 < .001 1.2 1.0 1.5 0.087
Age (≥80), years 19–49 3.5 1.8 6.6 < .001 2.6 1.0 6.5 < .05 2.6 1.3 5.4 < .01 1.9 1.3 3.0 < .01 0.9 0.5 1.5 0.589
50–59 2.8 1.9 4.2 < .001 3.2 1.7 6.0 < .001 3.0 1.9 4.9 < .001 1.8 1.3 2.5 < .001 0.9 0.6 1.3 0.531
60–69 2.8 2.1 3.8 < .001 3.5 2.4 5.3 < .001 3.4 2.5 4.6 < .001 2.0 1.6 2.7 < .001 1.0 0.8 1.4 0.803
70–79 1.9 1.5 2.5 < .001 2.3 1.7 3.2 < .001 2.1 1.7 2.8 < .001 1.8 1.4 2.3 < .001 1.2 1.0 1.6 0.108
Education level (no or primary) middle school 1.4 1.1 1.8 < .05 1.0 0.7 1.5 0.974 1.2 0.9 1.5 0.304 1.2 1.0 1.5 0.111 1.2 0.9 1.5 0.313
high school 1.8 1.4 2.4 < .001 1.3 0.9 2.0 0.180 1.6 1.2 2.2 < .01 1.7 1.4 2.1 < .001 1.4 1.0 1.8 < .05
college or higher 2.4 1.7 3.5 < .001 1.5 0.8 2.7 0.208 2.5 1.6 3.9 < .001 2.1 1.6 2.9 < .001 1.5 1.0 2.2 0.058
Marital status (single) currently married 1.5 0.8 2.8 0.246 1.1 0.5 2.4 0.863 1.6 0.8 3.1 0.199 1.1 0.7 1.8 0.600 1.4 0.8 2.3 0.198
formerly married 1.2 0.6 2.2 0.665 0.6 0.3 1.5 0.300 1.3 0.6 2.5 0.504 0.9 0.6 1.4 0.619 1.1 0.7 1.9 0.662
Employment status (unemployed) employed 1.7 1.3 2.1 < .001 2.4 1.6 3.5 < .001 1.5 1.2 2.0 < .01 1.3 1.0 1.5 < .05 1.4 1.1 1.8 < .01
self-employed 1.9 1.4 2.5 < .001 2.9 1.8 4.5 < .001 2.2 1.5 3.1 < .001 1.3 1.0 1.7 < .05 1.5 1.1 2.0 < .05
Household income quartile (1) 2 1.2 0.9 1.5 0.131 1.0 0.7 1.4 0.933 1.1 0.8 1.4 0.526 1.2 1.0 1.5 0.100 1.2 0.9 1.6 0.121
3 1.6 1.2 2.1 < .001 1.7 1.1 2.5 < .05 1.7 1.2 2.3 < .01 1.3 1.0 1.7 < .05 1.4 1.0 1.9 < .01
4 1.5 1.1 2.0 < .05 1.7 1.0 3.0 < .05 1.6 1.1 2.3 < .05 1.3 1.0 1.8 < .05 1.7 1.2 2.4 < .01
Disability (yes) no 3.6 2.7 4.7 < .001 3.9 2.8 5.4 < .001 3.4 2.6 4.6 < .001 2.1 1.6 2.7 < .001 1.4 1.1 1.9 < .05
No. of chronic conditions (≥3) 1 3.0 2.4 3.8 < .001 2.7 1.9 3.9 < .001 2.8 2.1 3.6 < .001 2.4 1.9 3.0 < .001 1.6 1.2 2.1 < .001
2 1.6 1.3 2.0 < .001 1.5 1.1 2.0 < .05 1.6 1.3 2.0 < .001 1.4 1.2 1.8 < .001 1.3 1.1 1.7 < .05
Health literacy (inadequate) marginal 1.5 1.2 1.8 < .001 1.6 1.1 2.2 < .05 1.4 1.1 1.8 < .01 1.0 0.8 1.2 0.751 1.0 0.8 1.2 0.732
adequate 1.5 1.2 2.0 < .001 1.6 1.0 2.3 < .05 1.6 1.2 2.2 < .01 1.0 0.8 1.3 0.916 1.4 1.1 1.9 < .05
Open in a new tab

Abbreviations: OR, Odds ratio; CI, Confidence interval.

In sum, these findings are worth reiterating with respect to the hypotheses formulated at the inception of this study. First, health literacy is positively associated with HRQoL in patients with chronic conditions. Not only adequate but also marginal health literacy are linked to improved HRQoL. Second, health literacy has a significant impact on mobility, self-care, usual activities, and anxiety/depression but not on pain/discomfort.

Discussion

This study shows that a combined total of 55.4% of Korean adults with chronic conditions have limited health literacy (30.8% for inadequate and 24.6% for marginal). This prevalence is more or less comparable to that in the general population of the U.S. [6], European countries [5,19,43], and Southeast Asian countries [44]. In the study presented here, adequate health literacy is positively associated with HRQoL among patients with chronic diseases, confirming the first hypothesis established at the outset and consistent with the findings of earlier studies [14,29,30].

The observed association may be explained by several mechanisms. First of all, health literacy can affect patients’ knowledge and belief about diseases that may be helpful to the management of chronic conditions [45]. For example, chronic obstructive pulmonary disease (COPD) patients with low health literacy are less likely to believe that they will always have the chronic condition and more likely to express concerns about medications [46], which could affect their adherence to treatment. Second, health literacy influences heath care utilization that may be necessary to appropriately manage chronic conditions [18,19]. For example, patients with chronic low back pain that have adequate health literacy are more likely to use medications and see a specialist than those with limited literacy. Medication adherence, in particular, appears to be influenced by health literacy [47]. This may partly by low literacy adversely influencing adult patients’ ability to correctly interpret warning labels for prescription drugs [48]. Third, adequate health literacy could positively affect patients’ engagement and empowerment in their self-care [19]. Patients with limited health literacy are more likely to experience difficulty using health materials received from health professionals, thereby negatively affecting their self-management and decision-making [49]. Adequate health literacy can be particularly important for patients with complex chronic diseases who need to be actively involved in their own care [50]. Diabetes patients with limited literacy have a higher risk of physical inactivity and unhealthy diet [51].

The proportion of participants reporting moderate or severe problems is highest in people with inadequate literacy and lowest in those with adequate literacy in all five dimensions of EQ-5D. However, after adjustments for covariates, adequate health literacy is associated with the odds of reporting no problems with self-care, mobility, usual activities, and anxiety/depression only. The existing literature supports the link between these specific dimensions of HRQoL and health literacy, based on some demographic groups [52,53] and a few common chronic conditions [54,55]. For example, the significant influence of health literacy on self-care behaviors has been documented in patients with diabetes [54], hypertension [55], and heart failure [56]. Adequate health literacy is linked to lower disease activity and improved physical functioning among patients with rheumatic diseases [57]. A number of studies find that better health literacy is associated with lower risks for anxiety and depressive symptoms [52,58–60]. Consistent with the findings, this current study shows that adults with adequate literacy are more likely to report no problems with anxiety/depression than those with inadequate literacy. It is plausible that adequate literacy may help patients cope with mental conditions associated with chronic diseases.

Health literacy has been shown to be inversely associated with pain intensity among patients with musculoskeletal pain [61] and those with chronic pain [62]. One possible explanation for the relationship points to the role of health literacy in better pain management [62]. Limited health literacy adversely influences knowledge about overall pain medication and non-medication modes of pain management [63]. However, this current study does not support the link between health literacy and the pain/discomfort dimension of EQ-5D. The contradictory finding may have to do with the choice of the study population; this present study is not limited to patients suffering from pain but based on a sample of adults with any of chronic conditions.

This study shows that health literacy is positively associated with the EQ-5D index among adults with chronic diseases. In addition, adults with adequate health literacy are more likely to report no problems with mobility, self-care, usual activities, and anxiety/depression, but not with pain/discomfort, which confirms the hypotheses of this study. These findings have the following implications. First, inadequate health literacy is so prevalent in adults with chronic diseases that across-the-board public health interventions to improve health literacy is warranted. Efforts to improve health literacy among adults with chronic conditions can be particularly important since patient-reported HRQoL is deteriorated in chronically ill patients. Second, the development of health literacy interventions should prioritize vulnerable subpopulations based on sociodemographic and health-related characteristics for improved efficiency.

This study has the following limitations. First, this analysis of cross-sectional data cannot establish a causal relationship between health literacy and HRQoL. Second, this study is based on self-reported data on chronic conditions and other characteristics and therefore may be subject to recall and reporting biases. Third, a substantial ceiling effect is reported for rating of EQ-5D by patients with chronic conditions [26]. Future research should explore the possibility of using other measures of HRQoL.

Conclusion

This population-based study shows that limited health literacy is a prevalent problem in adults with chronic diseases in Korea. Adequate health literacy is associated with better HRQoL. Health literacy has a differential impact across dimensions of HRQoL. Adequate health literacy is a protective factor for four dimensions of EQ-5D (mobility, self-care, usual activities, and anxiety/depression). Considering the high prevalence and its negative impact on HRQoL, limited health literacy should be recognized as a public health concern among adults with chronic diseases.

Data Availability

The data is owned by a third party and the authors had no special access privileges others would not have. A request for the data used for this study can be made on https://www.khp.re.kr:444/eng/data/data.do. Inquiries regarding data acquisition should be sent to the Korea Institute for Health and Social Affairs (email: khp@kihasa.re.kr).

Funding Statement

The author(s) received no specific funding for this work.

References

  • 1.Berkman ND, Sheridan SL, Donahue KE, Halpern DJ, Crotty K. Low health literacy and health outcomes: an updated systematic review. Ann Intern Med. 2011;155: 97–107. doi: 10.7326/0003-4819-155-2-201107190-00005 [DOI] [PubMed] [Google Scholar]
  • 2.Cho YI, Lee S-YD, Arozullah AM, Crittenden KS. Effects of health literacy on health status and health service utilization amongst the elderly. Soc Sci Med. 2008;66: 1809–1816. doi: 10.1016/j.socscimed.2008.01.003 [DOI] [PubMed] [Google Scholar]
  • 3.Institute of Medicine. Health Literacy: A Prescription to End Confusion. Washington DC: National Academies Press; 2004. [PubMed] [Google Scholar]
  • 4.Sørensen K, Van den Broucke S, Fullam J, Doyle G, Pelikan J, Slonska Z, et al. Health literacy and public health: A systematic review and integration of definitions and models. BMC Public Health. 2012;12: 80. doi: 10.1186/1471-2458-12-80 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Sørensen K, Pelikan JM, Röthlin F, Ganahl K, Slonska Z, Doyle G, et al. Health literacy in Europe: comparative results of the European health literacy survey (HLS-EU). Eur J Public Health. 2015;25: 1053–1058. doi: 10.1093/eurpub/ckv043 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Paasche-Orlow MK, Parker RM, Gazmararian JA, Nielsen-Bohlman LT, Rudd RR. The Prevalence of Limited Health Literacy. J Gen Intern Med. 2005;20: 175–184. doi: 10.1111/j.1525-1497.2005.40245.x [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Bostock S, Steptoe A. Association between low functional health literacy and mortality in older adults: longitudinal cohort study. BMJ. 2012;344: e1602. doi: 10.1136/bmj.e1602 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Bae J, Kim H. Health Literacy in Korea: Findings from a Nationally Representative Survey. Sejong Korea: Korea Institute for Health and Social Affairs; 2023. Feb. [Google Scholar]
  • 9.Kwon S. Thirty years of national health insurance in South Korea: lessons for achieving universal health care coverage. Health Policy and Planning. 2009;24: 63–71. doi: 10.1093/heapol/czn037 [DOI] [PubMed] [Google Scholar]
  • 10.Kim M, Lavonen J, Ogawa M. Experts’ Opinions on the High Achievement of Scientific Literacy in PISA 2003: A Comparative Study in Finland and Korea. EURASIA J Math Sci Tech Ed. 2009;5: 379–393. doi: 10.12973/ejmste/75288 [DOI] [Google Scholar]
  • 11.Kwon SK, Lee M, Shin D. Educational Assessment in the Republic of Korea: Lights and Shadows of High-Stake Exam-Based Education System. Assessment in Education: Principles, Policy & Practice. 2017;24: 60–77. doi: 10.1080/0969594X.2015.1074540 [DOI] [Google Scholar]
  • 12.Balakrishnan MP, Herndon JB, Zhang J, Payton T, Shuster J, Carden DL. The Association of Health Literacy With Preventable Emergency Department Visits: A Cross-sectional Study. Acad Emerg Med. 2017;24: 1042–1050. doi: 10.1111/acem.13244 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13.Parker RM, Baker DW, Williams MV, Nurss JR. The test of functional health literacy in adults. J Gen Intern Med. 1995;10: 537–541. doi: 10.1007/BF02640361 [DOI] [PubMed] [Google Scholar]
  • 14.Koole D, Lans A, Lang JH, de Groot TM, Borkhetaria P, Verlaan J-J, et al. Limited Health Literacy Results in Lower Health-Related Quality of Life in Spine Patients. SPINE J. 2023;online. doi: 10.1016/j.spinee.2023.09.016 [DOI] [PubMed] [Google Scholar]
  • 15.Ownby RL, Acevedo A, Jacobs RJ, Caballero J, Waldrop-Valverde D. Quality of life, health status, and health service utilization related to a new measure of health literacy: FLIGHT/VIDAS. Patient Educ Couns. 2014;96: 404–410. doi: 10.1016/j.pec.2014.05.005 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Duong VT, Lin I-F, Sorensen K, Pelikan JM, Van Den Broucke S, Lin Y-C, et al. Health Literacy in Taiwan: A Population-Based Study. Asia Pac J Public Health. 2015;27: 871–880. doi: 10.1177/1010539515607962 [DOI] [PubMed] [Google Scholar]
  • 17.AHLA. Asian Health Literacy Association. [cited 1 Mar 2024]. Available: https://www.ahla-asia.org/service/6.htm.
  • 18.Song I, Lee SH. COVID-19 vaccine refusal associated with health literacy: findings from a population-based survey in Korea. BMC Public Health. 2023;23: 255. doi: 10.1186/s12889-023-15182-0 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Palumbo R, Annarumma C, Adinolfi P, Musella M, Piscopo G. The Italian Health Literacy Project: Insights from the assessment of health literacy skills in Italy. Health Policy. 2016;120: 1087–1094. doi: 10.1016/j.healthpol.2016.08.007 [DOI] [PubMed] [Google Scholar]
  • 20.Puente-Maestu L, Calle M, Rodríguez-Hermosa JL, Campuzano A, de Miguel Díez J, Álvarez-Sala JL, et al. Health literacy and health outcomes in chronic obstructive pulmonary disease. Respir Med. 2016;115: 78–82. doi: 10.1016/j.rmed.2016.04.016 [DOI] [PubMed] [Google Scholar]
  • 21.Eichler K, Wieser S, Brügger U. The costs of limited health literacy: a systematic review. Int J Public Health. 2009;54: 313–324. doi: 10.1007/s00038-009-0058-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Dunn P, Conard S. Improving health literacy in patients with chronic conditions: A call to action. Int J Cardiol. 2018;273: 249–251. doi: 10.1016/j.ijcard.2018.08.090 [DOI] [PubMed] [Google Scholar]
  • 23.Aboumatar HJ, Carson KA, Beach MC, Roter DL, Cooper LA. The Impact of Health Literacy on Desire for Participation in Healthcare, Medical Visit Communication, and Patient Reported Outcomes among Patients with Hypertension. J Gen Intern Med. 2013;28: 1469–1476. doi: 10.1007/s11606-013-2466-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Katz P, Dall’Era M, Trupin L, Rush S, Murphy LB, Lanata C, et al. Impact of Limited Health Literacy on Patient-Reported Outcomes in Systemic Lupus Erythematosus. Arthritis Care Res. 2021;73: 110–119. doi: 10.1002/acr.24361 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Mielck A, Vogelmann M, Leidl R. Health-related quality of life and socioeconomic status: inequalities among adults with a chronic disease. Health Qual Life Outcomes. 2014;12: 58. doi: 10.1186/1477-7525-12-58 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Saarni SI, Härkänen T, Sintonen H, Suvisaari J, Koskinen S, Aromaa A, et al. The Impact of 29 Chronic Conditions on Health-related Quality of Life: A General Population Survey in Finland Using 15D and EQ-5D. Qual Life Res. 2006;15: 1403–1414. doi: 10.1007/s11136-006-0020-1 [DOI] [PubMed] [Google Scholar]
  • 27.Alonso J, Ferrer M, Gandek B, Ware JE, Aaronson NK, Mosconi P, et al. Health-related quality of life associated with chronic conditions in eight countries: Results from the International Quality of Life Assessment (IQOLA) Project. Qual Life Res. 2004;13: 283–298. doi: 10.1023/b:qure.0000018472.46236.05 [DOI] [PubMed] [Google Scholar]
  • 28.Wang C, Kane RL, Xu D, Meng Q. Health literacy as a moderator of health-related quality of life responses to chronic disease among Chinese rural women. BMC Women’s Health. 2015;15: 34. doi: 10.1186/s12905-015-0190-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Nacanabo R, Debussche X, Rouamba M, Kamouni P, Mancini J, Kouanda S. Health literacy and health-related quality of life in type 2 diabetes: A cross-sectional study in Burkina Faso. Diabetes Epidemiol Manag. 2021;3: 100016. doi: 10.1016/j.deman.2021.100016 [DOI] [Google Scholar]
  • 30.Sayah FA, Qiu W, Johnson JA. Health literacy and health-related quality of life in adults with type 2 diabetes: a longitudinal study. Qual Life Res. 2016;25: 1487–1494. doi: 10.1007/s11136-015-1184-3 [DOI] [PubMed] [Google Scholar]
  • 31.Gaffari-fam S, Lotfi Y, Daemi A, Babazadeh T, Sarbazi E, Dargahi-Abbasabad G, et al. Impact of health literacy and self-care behaviors on health-related quality of life in Iranians with type 2 diabetes: a cross-sectional study. Health Qual Life Outcomes. 2020;18: 357. doi: 10.1186/s12955-020-01613-8 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Korea Institute for Health and Social Affairs. Korea Health Panel Survey: Survey Design. [cited 10 Oct 2023]. Available: https://www.khp.re.kr:444/eng/survey/sampling.do.
  • 33.Chun H, Lee JY. Factors associated with health literacy among older adults: Results of the HLS-EU-Q16 measure. Korean J Health Educ Promot. 2020;37: 1–13. [Google Scholar]
  • 34.Duong TV, Aringazina A, Kayupova G, Nurjanah null, Pham TV, Pham KM, et al. Development and Validation of a New Short-Form Health Literacy Instrument (HLS-SF12) for the General Public in Six Asian Countries. Health Lit Res Pract. 2019;3: e91–e102. doi: 10.3928/24748307-20190225-01 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Megari K. Quality of Life in Chronic Disease Patients. Health Psychol Res. 2013;1: e27. doi: 10.4081/hpr.2013.e27 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 36.Devlin NJ, Brooks R. EQ-5D and the EuroQol Group: Past, Present and Future. Appl Health Econ Health Policy. 2017;15: 127–137. doi: 10.1007/s40258-017-0310-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Solli O, Stavem K, Kristiansen I. Health-related quality of life in diabetes: The associations of complications with EQ-5D scores. Health Qual Life Outcomes. 2010;8: 18. doi: 10.1186/1477-7525-8-18 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Lee Y-K, Nam H-S, Chuang L-H, Kim K-Y, Yang H-K, Kwon I-S, et al. South Korean time trade-off values for EQ-5D health states: modeling with observed values for 101 health states. Value Health. 2009;12: 1187–1193. doi: 10.1111/j.1524-4733.2009.00579.x [DOI] [PubMed] [Google Scholar]
  • 39.Heyworth IT, Hazell ML, Linehan MF, Frank TL. How do common chronic conditions affect health-related quality of life? Br J Gen Pract. 2009;59: e353–e358. doi: 10.3399/bjgp09X453990 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 40.Han K-T, Kim SJ, Song H, Chun S-Y, Kim CO, Kim J-S, et al. Associations between quality of life and marital status in cancer patients and survivors. Asian Pac J Cancer Prev. 2014;15: 5287–5291. doi: 10.7314/apjcp.2014.15.13.5287 [DOI] [PubMed] [Google Scholar]
  • 41.Lipsitz SR, Fitzmaurice GM, Sinha D, Hevelone N, Giovannucci E, Hu JC. Testing for independence in J × K contingency tables with complex sample survey data. Biometrics. 2015;71: 832–840. doi: 10.1111/biom.12297 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 42.Hahs-Vaughn DL, McWayne CM, Bulotsky-Shearer RJ, Wen X, Faria A-M. Methodological considerations in using complex survey data: an applied example with the head start family and child experiences survey. Eval Rev. 2011;35: 269–303. doi: 10.1177/0193841X11412071 [DOI] [PubMed] [Google Scholar]
  • 43.Baccolini V, Rosso A, Di Paolo C, Isonne C, Salerno C, Migliara G, et al. What is the Prevalence of Low Health Literacy in European Union Member States? A Systematic Review and Meta-analysis. J Gen Intern Med. 2021;36: 753–761. doi: 10.1007/s11606-020-06407-8 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Rajah R, Hassali MAA, Murugiah MK. A systematic review of the prevalence of limited health literacy in Southeast Asian countries. Public Health. 2019;167: 8–15. doi: 10.1016/j.puhe.2018.09.028 [DOI] [PubMed] [Google Scholar]
  • 45.Mackey LM, Doody C, Werner EL, Fullen B. Self-Management Skills in Chronic Disease Management: What Role Does Health Literacy Have? Med Decis Making. 2016;36: 741–759. doi: 10.1177/0272989X16638330 [DOI] [PubMed] [Google Scholar]
  • 46.Kale MS, Federman AD, Krauskopf K, Wolf M, O’Conor R, Martynenko M, et al. The Association of Health Literacy with Illness and Medication Beliefs among Patients with Chronic Obstructive Pulmonary Disease. PLOS ONE. 2015;10: e0123937. doi: 10.1371/journal.pone.0123937 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 47.Glassman SD, Carreon LY, Brown ME, Jones JS, Edward J, Li J, et al. The impact of health literacy on health status and resource utilization in lumbar degenerative disease. Spine J. 2019;19: 711–716. doi: 10.1016/j.spinee.2018.10.012 [DOI] [PubMed] [Google Scholar]
  • 48.Davis TC, Wolf MS, Bass PF, Middlebrooks M, Kennen E, Baker DW, et al. Low Literacy Impairs Comprehension of Prescription Drug Warning Labels. J Gen Intern Med. 2006;21: 847–851. doi: 10.1111/j.1525-1497.2006.00529.x [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 49.Sahm LJ, Wolf MS, Curtis LM, McCarthy S. Prevalence of Limited Health Literacy Among Irish Adults. J Health Commun. 2012;17: 100–108. doi: 10.1080/10810730.2012.718041 [DOI] [PubMed] [Google Scholar]
  • 50.Abdullah A, Liew SM, Salim H, Ng CJ, Chinna K. Prevalence of limited health literacy among patients with type 2 diabetes mellitus: A systematic review. PLOS ONE. 2019;14: e0216402. doi: 10.1371/journal.pone.0216402 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 51.Friis K, Vind BD, Simmons RK, Maindal HT. The Relationship between Health Literacy and Health Behaviour in People with Diabetes: A Danish Population-Based Study. J Diabetes Res. 2016;2016: e7823130. doi: 10.1155/2016/7823130 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 52.Eronen J, Paakkari L, Portegijs E, Saajanaho M, Rantanen T. Assessment of health literacy among older Finns. Aging Clin Exp Res. 2019;31: 549–556. doi: 10.1007/s40520-018-1104-9 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 53.Wolf MS, Gazmararian JA, Baker DW. Health literacy and functional health status among older adults. Arch Intern Med. 2005;165: 1946–1952. doi: 10.1001/archinte.165.17.1946 [DOI] [PubMed] [Google Scholar]
  • 54.RobatSarpooshi D, Mahdizadeh M, Alizadeh Siuki H, Haddadi M, Robatsarpooshi H, Peyman N. The Relationship Between Health Literacy Level and Self-Care Behaviors in Patients with Diabetes. Patient Relat Outcome Meas. 2020;11: 129–135. doi: 10.2147/PROM.S243678 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 55.Darvishpour A, Mansour-Ghanaei R, Mansouri F. The Relationship Between Health Literacy, Self-Efficacy, and Self-Care Behaviors in Older Adults With Hypertension in the North of Iran. Health Lit Res Pract. 2022;6: e262–e269. doi: 10.3928/24748307-20221013-01 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 56.Erünal M, Mert H. Does Health Literacy Affect Self-Care in Patients with Heart Failure? J Nurse Pract. 2020;16: 699–702. doi: 10.1016/j.nurpra.2020.07.016 [DOI] [Google Scholar]
  • 57.Zhang X-H, Li S-C, Fong K-Y, Thumboo J. The Impact of Health Literacy on Health-Related Quality of Life (HRQoL) and Utility Assessment among Patients with Rheumatic Diseases. Value Health. 2009;12: S106–S109. doi: 10.1111/j.1524-4733.2009.00640.x [DOI] [PubMed] [Google Scholar]
  • 58.Lincoln A, Paasche-Orlow MK, Cheng DM, Lloyd-Travaglini C, Caruso C, Saitz R, et al. Impact of Health Literacy on Depressive Symptoms and Mental Health-related: Quality of Life Among Adults with Addiction. J Gen Intern Med. 2006;21: 818–822. doi: 10.1111/j.1525-1497.2006.00533.x [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 59.Haruyama Y, Miyagi E, Kobashi G, Obata S, Umazume T, Yoshimi A, et al. Impact of health literacy on anxiety and depressive symptoms in pregnant women in Japan during the COVID-19 pandemic. Sci Rep. 2022;12: 14042. doi: 10.1038/s41598-022-18405-3 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 60.Magallón-Botaya R, Méndez-López F, Oliván-Blázquez B, Carlos Silva-Aycaguer L, Lerma-Irureta D, Bartolomé-Moreno C. Effectiveness of health literacy interventions on anxious and depressive symptomatology in primary health care: A systematic review and meta-analysis. Front Public Health. 2023;11: 1007238. doi: 10.3389/fpubh.2023.1007238 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 61.Bittencourt JV, de Souza PAC, Corrêa LA, Volotão AN, Mathieson S, Nogueira LAC. Health literacy, pain-related interference and pain-related distress of patients with musculoskeletal pain. Health Promot Int. 2023;38: daab183. doi: 10.1093/heapro/daab183 [DOI] [PubMed] [Google Scholar]
  • 62.Köppen PJ, Dorner TE, Stein KV, Simon J, Crevenna R. Health literacy, pain intensity and pain perception in patients with chronic pain. Wien Klin Wochenschr. 2018;130: 23–30. doi: 10.1007/s00508-017-1309-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 63.Devraj R, Herndon CM, Griffin J. Pain awareness and medication knowledge: a health literacy evaluation. J Pain Palliat Care Pharmacother. 2013;27: 19–27. doi: 10.3109/15360288.2012.751955 [DOI] [PubMed] [Google Scholar]

Decision Letter 0

Uwe Konerding

2 Feb 2024

PONE-D-23-40500Relationship between health literacy and health-related quality of life in Korean adults with chronic diseasesPLOS ONE

Dear Dr. Song,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

As it is very difficult to get reviewers, I have performed one of the two reviews myself. I am reviewer 2. Except for two comments, I also agree with the comments of reviewer 1. One comment with which I do not agree is the first reviewer’s comment regarding binomial logistic regression. As far as I can see you have applied this kind of regression in exactly those cases in which it is necessary. A further comment with which I not completely agree is given in the first paragraph regarding the results. In contrast to reviewer 1, I do not think that the description is too brief. However, I share with reviewer 1 a feeling of not being completely satisfied with this description. My problem is caused by the fact that you mainly repeat the information given in the tables. I would like to have a description that focusses more on the more essential aspects in the data, i.e., that you already elaborate and highlight what is especially important. This might be similar with what reviewer 1 meant with: ‘A more detailed description in terms of striking or special results would be useful. Especially those that are to be discussed.’

I must also give two comments that I forgot in my review. The first comment regards the fact that you use the Rao-Scott chi-square test for testing differences between categorial variables. The usual approach is applying that chi-square test that has originally been presented by Pearson and that is presented in textbooks as the classical approach for analyzing cross-tables. Please, explain what the Rao-Scott chi-square test distinguishes from the Pearson chi-square and why you think that choosing this statistic is more appropriate for your problem. If there is no special reason for choosing the Rao-Scott chi-square test I would like you to rerun the corresponding analyses with Pearson’s chi-square. This statistic has the simplest and clearest meaning. The second additional comment regards the footnote of table 3. This footnote is: ‘p-values were obtained by using the Rao-Scott chi-square test and the ANOVA.’ This makes no sense because you report only one p-value per test and an ANOVA would not be appropriate in this context. Please report the one and only statistical procedure you have actually applied.

==============================

Please submit your revised manuscript by Mar 18 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Uwe Konerding

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at 

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and 

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. In the online submission form, you indicated that your data is available only on request from a third party. Please note that your Data Availability Statement is currently missing [the name of the third party contact or institution / contact details for the third party, such as an email address or a link to where data requests can be made]. Please update your statement with the missing information. 

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Dear author,

Many thanks for the exciting manuscript. The presentation is largely solid. Below are a few points that could supplement the manuscript

In general, the work of the Asian Health Literacy Association (AHLA), of which South Korea is also a member, could be discussed in a few sentences. This would be of interest to the international readership. For articles on national aspects of health literacy, it would be helpful to add national circumstances (education system, socioeconomics, utilisation of the healthcare system). This does not have to be described in detail. But appropriate sources would be helpful.

Introduction

The work of the AHLA could be mentioned in the introduction. In addition, something should be mentioned about the Korean education system in the context of health literacy so that the international readership can categorise it.

Otherwise, the points listed above would be useful in the introduction.

Methods:

Justify the use of HLS-EU 16! At the time of the study, the HLS-SF12 had already been successfully validated in Asia [Duong et al., 2019].

The choice of covariates should be justified. Most of them are plausible. However, for example, the severity of an illness rather than the number of illnesses seems to me to be more important. Or number of household members seems more logical to me than marital status. Please explain the choice of covariates.

When carrying out the logistic regression analysis, the question arises as to why binomial logistic regression was not used for dichotomous (binary) dependent variables. Please explain! In many places, the binomial variant would have been more meaningful.

Results

The results are presented in a solid table. However, the description of the results is rather brief. A more detailed description in terms of striking or special results would be useful. Especially those that are to be discussed.

With regard to the hypotheses mentioned in the introduction, the presentation of the results should also be expanded in this respect.

Discussion

The discussion is sound and the limitations are clearly stated. However, the concept of hypothesis could also be included here.

Conclusion

Conclusion can be drawn!

see method:

Duong TV, Aringazina A, Kayupova G, Nurjanah, Pham TV, Pham KM, Truong TQ, Nguyen KT, Oo WM, Su TT, Majid HA, Sørensen K, Lin IF, Chang Y, Yang SH, Chang PWS. Development and Validation of a New Short-Form Health Literacy Instrument (HLS-SF12) for the General Public in Six Asian Countries. Health Lit Res Pract. 2019 Apr 10;3(2):e91-e102. doi: 10.3928/24748307-20190225-01.]

Reviewer #2: Review regarding the manuscript ‘Relationship between health literacy and health-related quality of life in Korean adults with chronic diseases’

A study regarding the relationship between health literacy and health-related quality of life in Korean adults with chronic diseases is presented in the manuscript. The study is performed with cross-sectional data taken from the Korea Health Panel Survey from 2021. The topic of the manuscript is interesting. The analyses are methodologically sound, and the different consideration are well ordered. However, there are several minor flaws. Most of them refer to the language. I have tried to address all of these flaws, including those regarding the language. However, I am not a native speaker of the English language. Therefore, I recommend having the manuscript being checked by a native speaker. Should this person make different propositions than I make, please discuss this with the native speaker and choose that solution that the native speaker and you finally prefer. In the following text, you find the numerous minor flaws that should be corrected before publication.

Lines 21-22

‘This aims to examine the relationship between health literacy and HRQoL among Korean adults with chronic conditions. This cross-sectional study was based on the Korea Health Panel Survey in 2021.’

I suggest replacing this by

‘In this contribution, the relationship between health literacy and HRQoL in Korean adults with chronic conditions is examined using data of the cross-sectional Korea Health Panel Survey from 2021.’

Line 25 and further text

I suggest replacing

‘EQ-5D index score’

by

‘EQ-5D index’

An index is a score. Therefore, ‘EQ-5D index score’ is one word too much.

Lines 26 to 28

‘Multiple logistic regression models were implemented for domain-specific outcomes. In the weighted sample, 30.8%, 24.6%, and 44.6% had inadequate, marginal, and adequate levels of health literacy, respectively.’

A reader who has not read your manuscript cannot know what you meant by ‘domain-specific’ and, even a reader who has read you manuscript does not know what you mean by weighted by ‘weighted’? (See below)

Please revise the corresponding parts of the main text according to my suggestions and revise the abstract correspondingly.

Lines 28 to 30

‘EQ-5D index scores were positively associated with marginal (B=0.018, p<0.001) and adequate literacy (B=0.017, p<0.001) compared to inadequate literacy.’

I suggest writing

‘The EQ-5D index increases with marginal (B=0.018, p<0.001) and adequate literacy (B=0.017, p<0.001) compared to inadequate literacy.’

Lines 34 to 35

‘Inadequate health literacy is prevalent among Korean adults with chronic diseases.’

Should be reported earlier.

*****

Lines 47 to 48

‘Nearly a half of adults in the U.S. have limited health literacy according a systematic review [6].’

I suggest replacing this by

‘According to a systematic review [6], nearly a half of adults in the U.S. have limited health literacy.’

Line 48

I suggest replacing ‘meaning’ by ‘which means that’.

Lines 49 to 51

I suggest replacing

‘Nearly one in two adults aged 19 years and over in Korea have limited health literacy to make informed decision regarding their own health [8].’

By

‘In Korea, nearly one in two adults aged 19 years and over has limited health [8].’ The term ‘to make informed decision regarding their own health’ is not helpful in this sentence. The remaining changes regard the language.’

Line 57

Please replace ‘component to effective treatment’ by ‘component of effective treatment’.

Line 59

Please replace ‘negatively can’ by ‘can negatively’.

Line 65

With regard to the language, you should replace ‘Reflective of’ by ‘Reflecting’ or ‘Being reflective of’. However, there is still a further problem in the sentence. HRQoL-indices as the EQ-5D-index do not reflect the individual experience. They reflect societal values.

Line 65 to 77

Please report findings in present tense. They are usually meant to be generalizable over time.

Line 70 to 71

Replace ‘Type 2 diabetes is a chronic condition that garnered particular attention in relation to health literacy [22–24]’ by ‘A chronic condition that garnered particular attention in relation to health literacy is type 2 diabetes [22–24]’.

Line 77

Please replace ‘Also’ by ‘Moreover’ or ‘Further’ or ‘Furthermore’.

Line 78

Please omit ‘using survey data based on a nationally representative large sample of the population’. Inserting this phrase makes the sentence very difficult to understand. Please give this information in the first sentence of the methods part.

Lines 83 and 84

Please formulate the hypotheses in present tense (see above).

Line 91

‘city vs. province’

Why ‘vs’? I cannot be certain about what you want to say, but I guess the formulation ‘or, respectively,’ accords more to what you might want to express.

Line 92

The word ‘dong’ belongs to American slang and means, with absolute certainty, something that you do not want to talk about in this manuscript. The word ‘eup’ is not an English word at all. Please use English words. Moreover, my comment regarding ‘vs’ also applies to this line.

Line 95

I would leave out ‘presenting a rare opportunity to examine the hypotheses posited above’.

Line 111 to 119

I am not certain how this paragraph is meant. Is it a list of different health literacy measurement instruments included in the survey or is it consideration of the development of these measurement over time? If the first is true, you should make this clear. For example, you could write ‘KHPS contained several questionnaires addressing health literacy. These questionnaires are….’. If the second is true, this part belongs into the introduction.

Line 120 to 128

Please give first the general description of the HLS-EU-Q16 and then the report of the cultural adaptation.

Lines 131 to 142

You should report that each dimension of the EQ-5D is addressed by exactly one item, and you should replace the formulation ‘domain specific responses’ by the formulation ‘responses to the individual EQ-5D items’ throughout the complete manuscript. This will make your presentation easier to understand.

Sub-chapter ‘Covariates’

Please, tell the reader purpose for which you want to control for confounding variables and why you believe that the variables you have included as possible confounders serve this purpose.

Line 149

'…classified as ≤primary, middle school, high school, and ≥college’

What do the symbols ‘≤’ and ‘≥’ mean in this context? I guess that they should be omitted.

Line 150

Please replace ‘ever married’ by ‘formerly been married’.

Line 151

I suggest using the denominations ‘employed’, ‘self-employed’ and ‘un-employed’ for categorizing employment status.

Sub-chapter ‘Statistical analysis’

Past-tense sounds better and is more often used in the analysis sub-chapter.

Line 164

As far as I can infer from your text, you actually apply multivariate and not multivariable regression. As far as I know, multivariable regression is a regression with more than one dependent variable.

Lines 169 to 170

‘All analyses adjusted for sampling weights that are used in the complex sampling design of the 2021 KHPS.’

I have no idea what is done here. Please explain in the text. What is weighted by what? To which purpose is this weighting performed? How is the weighting integrated in the analyses?

Chapter ‘results’

I would use present tense throughout this chapter.

Line 175

What do you want to say with ‘In all’ in this context?

Please replace ‘received’ by ‘had’.

Line 182

Please place the adverb after the verb.

Chapter ‘Discussion’

I also would use present tense in this chapter. Moreover, this chapter is very long detailed. Most readers would be thankful if you shortened the discussion to a half of the present length and focus on the more general aspects.

Line 219

Please replace ‘this present study’ by ‘the study presented here’.

Lines 220 to 222

‘In particular, multi-morbidity appears to be an influential factor to the prevalence of inadequate health literacy, which increased in patients with a greater number of chronic conditions.’

You have cross-sectional data. Therefore, you cannot infer from your data whether a relationship between two variables results from one variable influencing the other, neither can you, in case of an influence, infer from the data, which of the two variables is the cause and which the effect. Youd mention something like this later as limitation. Accordingly, you should be cautious with using words as influence in this context. Of course, you can speculate about causal relationships as far as additional knowledge regarding the object of investigating allows for. However, given my knowledge regarding the object of investigation I see only a few mechanisms in which multi-morbidity could influence health literacy. To be specific, I do think that dementia reduces health literacy. However, I actually assume that health literacy influences multi-morbidity. To be specific, the higher the health literacy is the more people behave in a health-promoting way and, consequently, the less people suffer from multi-morbidity. In the further text, you develop similar thoughts. You should make the text in lines 220 to 222 consistent with this line of thinking.

Lines 238 to 240

‘This may be in part because low literacy adversely influenced adult patients’ ability to correctly interpret warning labels for prescription drugs [40].’

I suggest

‘This may partly be caused by low literacy adversely influencing adult patients’ ability to correctly interpret warning labels for prescription drugs [40].’

Lines 252 to 254

‘However, after adjustments for covariates, adequate and marginal health literacy were associated with the odds of reporting no problems with self-care, mobility, and usual activities only.’

I would restrict to the category of adequate health literacy and, accordingly, include anxiety/depression into the set of dimensions associated with health literacy.

Line 254

If you follow my suggestion to replace ‘domain specific responses’ by the formulation ‘responses to the individual EQ-5D items’ then you should replace in line 254 ‘domains’ by ‘dimensions’.

Chapter ‘Conclusion’ please also in present tense.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: Uwe Konerding

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Decision Letter 1

Uwe Konerding

26 Mar 2024

Relationship between health literacy and health-related quality of life in Korean adults with chronic diseases

PONE-D-23-40500R1

Dear Dr. Song,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Uwe Konerding

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Dear Author,

Congratulations on the successful revision. All my comments and questions have been fully or sufficiently addressed and taken into account.

As far as the use of the HLS-EU12 is concerned, I suspect that due to a long planning and realisation period, the validation ran right into the implementation phase and therefore no further adjustments could be made.

I therefore recommend publication of the manuscript.

I wish you continued success!!!

Reviewer #2: You have addressed all of my comments. Now, the paper is fine. There are no objections to publication any longer.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

**********

Acceptance letter

Uwe Konerding

29 Mar 2024

PONE-D-23-40500R1

PLOS ONE

Dear Dr. Song,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

* All references, tables, and figures are properly cited

* All relevant supporting information is included in the manuscript submission,

* There are no issues that prevent the paper from being properly typeset

If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps.

Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

If we can help with anything else, please email us at customercare@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Uwe Konerding

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    Attachment

    Submitted filename: Rebuttal.docx

    pone.0301894.s001.docx (31.1KB, docx)

    Data Availability Statement

    The data is owned by a third party and the authors had no special access privileges others would not have. A request for the data used for this study can be made on https://www.khp.re.kr:444/eng/data/data.do. Inquiries regarding data acquisition should be sent to the Korea Institute for Health and Social Affairs (email: khp@kihasa.re.kr).

    Articles from PLOS ONE are provided here courtesy of PLOS

    RESOURCES