J Atherosclerosis Prev Treat. 2022 Sep-Dec;13(3):109–118 | doi:10.53590/japt.02.1040
Niki Mourouti, Maria Michou, Vassiliki Costarelli
Human Ecology Laboratory, Department of Economics & Sustainable Development Ecology, Harokopio University, Athens 17671, Greece
The article aims at presenting scientific evidence on the possible role of Health Literacy (HL) on hypertension health outcomes. Original-research studies published in English from January 1st 1990 to February 28th 2021, were selected through a computer-assisted literature search, using specific key words relating to hypertension and HL. Studies in full text, on adult hypertensive patients, were included. Out of the 56 articles reviewed, 29 publications met the criteria for inclusion. Twenty-four studies were cross-sectional, 2 studies were interventions and there was 1 study from each of the following categories: randomised control trial (RCT), retrospective study and a non-randomised prospective cohort trial. The findings differ according to the design of the study, however, there seems to be good evidence that higher HL is usually associated with better blood pressure control, better hypertension knowledge, better medication adherence and higher levels of health-related quality of life of the participants. There is evidence that health literacy levels positively affect hypertension health outcomes.
Key Words: Health literacy, hypertension, health outcomes, blood pressure, hypertension knowledge.
Corresponding author: Vassiliki Costarelli, Assοciate Professor, Harokopio University of Athens, Department of Economics & Sustainable Development, 70, E.Venizelou Ave, 17671 Kallithea, Athens-Greece, Tel.: +30 210 9549368, E-mail: firstname.lastname@example.org
Submission: 09.09.2022, Acceptance: 24.09.2022
Health Literacy (HL) has evolved into a broadly discussed and widely researched topic and it is defined as the possession of literacy skills that are required to make health related decisions, in a variety of different environments. Poor HL levels have been associated with higher use of emergency department services, lower uptake of preventive health-seeking behaviors, inadequate and/or poor knowledge of chronic diseases’ prevention and lower levels of reported quality of life1,2,3.
HL describes the cognitive and social skills which determine the motivation and ability of individuals to gain access to, understand and use information in ways which promote and maintain health4. The concept of HL is focusing at empowering people to live a healthier life5.
Nowadays, high blood pressure (BP) remains a major global public health issue6,7 and constitutes the leading preventable risk factor for premature death and disability, worldwide. The number of people with raised BP has increased by 90% worldwide in the past four decades, mainly due to the growth and ageing of the population, with the majority of the increase occurring in low-income and middle-income countries7.
Adequate levels of HL are of paramount importance in the management of hypertension since, successfully controlling and overcoming the condition, requires self-care management, self-efficacy, adherence to taking recommended drugs, as well as, certain diet and lifestyle modifications.
The aim of the article is to present and discuss the current scientific evidence on the possible role of HL on hypertension health outcomes, based on an extensive literature search.
MATERIALS AND METHODS
The PRISMA guidelines for reporting systematic reviews were followed here8. In particular, original-research studies that were published in English language from January 1st 1990 to February 28th 2021, were selected through a computer-assisted literature search (i.e., Medline via Pubmed and Scopus). The following key words were used: [“hypertension” OR “high blood pressure” OR “elevated blood pressure”] AND [“health literacy” OR “literacy”] (the terms numeracy, knowledge and medication literacy were not included in the search). In addition, the reference lists of the retrieved articles directed the search to relevant present articles that were not allocated through the searching procedure. Full text studies in English, focusing on the relationship of HL with health outcomes on adult hypertensive participants, were included. Studies referring to health numeracy, health knowledge or medication literacy, were excluded.
In total 1438 citations were yielded form all databases and three additional studies were included, through the reference list screen. After removal of duplicates, titles and abstracts were screened for relevance. The main reason for exclusion was not addressing HL and health outcomes in people with hypertension. Based on that, overall 56 articles were included for full-text review, out of which, 29 publications met the above criteria and are presented in the current article (Figure 1).
Figure 1. Flow diagram.
Characteristics of Included Studies
All of the studies included address the relationship between HL and health outcomes (Table 1). 24 of the studies were cross-sectional9-32, 2 studies were interventions33-34, 1 of them was RCT35 1 study was retrospective36 and 1 was a non-randomised prospective cohort trial37. The smallest study included 11 patients33 whereas the largest study included 46,263 patients19. Sixteen studies were conducted in the United States9-13,15-16,18-21,29,32-34,37, 4 were in Iran23,26,31,35, 2 were in China24,36, 2 were in Korea22,27, 1 was in Japan14, 1 was in Singapore17, 1 was in Turkey25, 1 was in Brazil28 and 1 was in Amsterdam30. The most commonly used instruments for HL assessment were Test of Functional Health Literacy (FHL) in Adults (TOFHLA), Short Test of FHL in Adults (S-TOFHLA), and Rapid Estimate of Adult Literacy in Medicine (REALM), Newest Vital Sign (NVS), Brief HL Screening (BHLS) and HL for Iranian Adults (HELIA).
HL and blood pressure outcomes
Systolic and/or Diastolic Blood Pressure
Nine studies examined the association between health literacy and systolic and/or diastolic blood pressure (SBP/DBP). Most studies demonstrated an inverse association between low or inadequate health literacy and BP. In a study conducted in 402 hypertensive patients9, it was concluded that low-literate patients had higher SBP while no association was found between literacy level and DBP. Similarly, it was concluded that when compared to patients with adequate literacy, the predicted mean SBP for patients with limited literacy, was higher12. A cross-sectional study (n=46.263 hospitalized adults), concluded that low health literacy was independently associated with elevated BP19. In another cross-sectional study with 423 urban, primary care hypertensive patients, low literacy was associated with uncontrolled BP (OR 1.75, 95%CI 1.06-2.87)20. Moreover, a retrospective cohort trial of 360 hypertensive patients indicated that SBP was significantly associated with health literacy after adjusting for potential confounders36, while Persell and his partners, also concluded that BP was higher in patients with inadequate health literacy (difference of 5.2/2.2 mmHg)11. In a literacy-focused high blood pressure (HBP) intervention in Spanish-speaking latinos with uncontrolled HBP, findings supported that participation in the intervention resulted in improved SBP and DBP33. On the other hand, in a cross-sectional study Willens et al. 201318 noticed that independent of educational attainment, 3-point increases in health literacy scores were associated with 0.74 mmHg higher SBP. In a non-randomized prospective cohort trial of 525 patients referred with uncontrolled hypertension, outcomes were assessed at 0, 6, 12, 18 and 24 months37.
Blood pressure control
Seven studies examined the association between health literacy and BP control. In a retrospective cohort trial of 360 hypertensive patients, the authors concluded that patients with high health literacy have better hypertension control36. In multivariate analyses, more limited literacy was found to be a significant, independent predictor of poorer hypertension control13. Furthermore, Costa et al. 201928 conducted a cross-sectional study with 392 hypertensive elderly people and resulted that in the inadequate BP control group (N=163), the prevalence of inadequate functional HL was higher (69.3%). A randomized controlled trial, with 118 elderly people with uncontrolled hypertension and inadequate HL showed that, after the intervention, the rates of uncontrolled systolic and diastolic blood pressures decreased; however, the between-group differences respecting these rates were not statistically significant (P > 0.05)35. Recently, in a cross-sectional study conducted in Iran31, it was found that controlling of systolic hypertension had a statistically significant negative correlation with all HL dimensions. On the contrary, in a cross-sectional survey conducted in Singapore, the achievement of target BP was not associated with HL level (p = 0.71) and there was no difference in the mean knowledge scores between the two BP control groups17. Similarly, Miranda et al., who conducted a large-scale prospective cohort study in a multi-ethnic population, resulted that no clear pattern was found in the association of health literacy with hypertension control30.
Five studies demonstrated that lower HL was associated with lower hypertension knowledge. In a cross-sectional study with 402 patients with hypertension conducted mean scores of knowledge were strongly related to literacy9. Similarly, in another cross-sectional study which included 214 patients with hypertension, 65 years or older, respondents with inadequate health literacy knew significantly less about their disease, than those with adequate literature10. Pandit and his partners recruited 330 hypertensive patients from six primary care safety net clinics and in multivariate analyses that did not make an adjustment for the other variable, lower literacy was found to be a significant independent predictor of poorer hypertension knowledge (grades 1–8 years of education: b = _0.89, 95% Confidence Interval (CI) – 1.76-0.02; category I of literacy skills: β = -2.04, 95% CI – 2.84-1.2413. A cross-sectional, interviewer-administered survey was performed at a government-funded primary care clinic in Singapore including 306 patients with hypertension, and the authors resulted that the hypertension knowledge scores were significantly associated with HL level (p<0.001)17. Finally, in a more recently published cross-sectional study conducted on 700 patients with hypertension, selected according to multistage random and quota types in the Isfahan province (Iran), there was a significant correlation between BP knowledge and mean score of health literacy26.
Six studies examined the association between health literacy and medication adherence in hypertension. Ingram and Ivanov 201316, examined the association of health literacy and adherence behaviors in African American older adults (N = 121) with hypertension using a descriptive correlational design. No statistically significant association was found between health literacy and adherence, but regression analysis showed that those who were younger and reported poor or fair health status, were less likely to adhere to treatment. In a cross-sectional study aiming to examine factors associated with medication adherence, medical-aid beneficiaries with higher health literacy and higher self-efficacy scores were more likely to have higher medication adherence, whereas, widowed and those who perceived more cons of chronic disease management, were more likely to have lower medication adherence than their counterparts (p < .05)22. In another randomized controlled trial with 118 elderly people with uncontrolled primary hypertension and inadequate health literacy, results indicate that after the intervention, medication adherence status in the intervention group was significantly better. (P = 0.002)35. In a cross-sectional survey of 1355 Hispanic adults, who self-reported hypertension, antihypertensive medication adherence and HL were evaluated along with covariates, including sociodemographic characteristics, depression, anxiety, and sleep disturbance. When controlling for age, sex, birth country, education level, recruitment location, depression, anxiety, and sleep disturbance, having adequate as compared to inadequate health literacy, was associated with a higher adherence score (b = 0.378, p = 0.043)29. Warren-Findlow et al. 201934 recruited 52 English and Spanish speaking patients with hypertension in a pilot study. Comparing baseline and follow-up hypertension self-care scores, barriers to medication adherence decreased and medication adherence increased; however, these changes were not statistically significant. Finally, in contrast to the above studies, in a cross-sectional study of 919 health center patients from the Chicago area with uncontrolled hypertension, 47.4% had likely limited (low), 33.2% possibly limited, and 19.4% likely adequate health literacy. Self-reported adherence to hypertension medications was higher among the low HL group (65.6% versus 56.0%, p=0.010)32.
Health-related Quality of Life (QoL)
Four studies demonstrated that HL was significantly associated with health-related quality of life. Naimi et al. 201723 in a cross-sectional study conducted in Tehran, Iran which consisted of 400 patients with hypertension, concluded that there was positive and significant correlation between HL and health-related QoL (p<0.01, r=0.30). In a retrospective cohort trial of 360 hypertensive patients, the goal was to determine factors associated with health literacy. Patients with high HL seemed to have better health-related QoL36. In a cross-sectional study published also in 2017, the aim was to examine the association between the health-related QoL of hypertensive patients and HL and self-management efficacy as well as how they affect the health-related QoL. The study demonstrated that HL was related to health-related QoL24. Moreover, in a descriptive cross-sectional study conducted in Korea, HL was significantly associated with health-related QoL in vulnerable older people with hypertension. It has to be stressed however that exercise and subjective health were more significant factors affecting health-related QoL than medical adherence and HL27.
Hypertension awareness: In a descriptive and cross-sectional research conducted among school teachers (78 out of 500 participants were hypertensive) in Turkey, adequate HL according to hypertension awareness and control in participants didn’t show any significance. Among people with hypertension, adequate HL was higher in those aware of the disease, than those not aware of being hypertensive (p > 0.05)25. Similarly, no significant associations were found between HL and hypertension awareness when Miranda et al. 201930 aimed to assess the extent to which HL affects hypertension prevalence, awareness, treatment and control, in different ethnic groups.
Illness perceptions: A cross-sectional study including 144 Hispanic adults with a self-reported diagnosis of hypertension, concluded that there were significantly weak to moderate relationships among acculturation, health literacy, and several illness perceptions. A significant moderate relationship was also found among acculturation, health literacy, and the Brief Illness Perception Questionnaire summary scores. Thus, as acculturation and HL increased, the perception decreased on how threatening hypertension is, as an illness. Even after controlling for demographic variables, acculturation and HL contributed significantly in explaining overall illness perceptions of hypertension, as indicated by the Brief Illness Perception Questionnaire summary scores21.
Medication reconciliation: Persell et al. 200711, in order to assess the relationship between health literacy, patient recall of antihypertensive medications, and reconciliation between patient self-report and the medical record, interviewed 119 patients with diagnosed hypertension and concluded that the agreement between patient-reported and medical record-reported antihypertensive medications, was lower for patients with inadequate, compared to adequate health literacy. In a more recently published cross-sectional study of patients from the Chicago area with uncontrolled hypertension, the authors demonstrated that compared to participants with likely adequate health literacy, participants with low HL were less likely to have chronic medications reconciled (18.0% versus 29.6%, p=0.007)32.
Participatory decision making (PDM): In a cross-sectional study of enrollment data from a randomized controlled trial of interventions to improve patient adherence to hypertension treatments with 275 urban patients with hypertension participating, it was also found that patients with low literacy were as interested in participating in decision making, as their counterparts with adequate literacy; however, they were less likely to experience PDM in their medical visits15.
Hypertension self-care: Warren-Findlow et al. 201934 recruited patients with hypertension to pilot test the acceptability and feasibility of a brief HL intervention focused on hypertension self-care and to assess changes in self-care activities. At 1-month follow-up, participants with inadequate literacy showed improvement on all self-care measures with significant mean differences (p < .05) on diet adherence and weight management activities.
Knowledge of drug indications: In a cross-sectional study of health center patients from the Chicago area with uncontrolled hypertension, the authors demonstrated that compared to participants with adequate health literacy, participants with low HL were less likely to know the indications for chronic medications (64.1% versus 83.1%, p<0.001)32.
Risk of Ischemic Cardiovascular Disease (ICVD): Shi et al. 201736 conducted a retrospective cohort trial of 360 hypertensive patients to investigate the determinants of HL and the potential relationship between HL and hypertension management. They concluded that patients with high HL have a lower risk of ischemic cardiovascular disease (ICVD).
Self-care management, empowerment, self-efficacy and adequate adherence to medication and diet/lifestyle modifications, are essential for the successful management of a chronic disease like hypertension38. The current systematic literature review was set out to investigate the possible role of HL on health outcomes in hypertension.
As anticipated, higher HL is usually associated with better BP control, better hypertension knowledge, better medication adherence and higher levels of health-related quality of life, however, findings differ in strength, according to the design of the study and the study population (general population vs vulnerable groups). The results of the studies are inconsistent (Table 1).
The above discrepancies could be partly attributed to certain methodological limitations in terms of design and recruitment method and the use of different instruments to assess the HL levels of the participants. More specifically, most of the studies conducted in this field, who met the review inclusion criteria, were not conducted in Europe, they were cross-sectional which are observational in nature, and they were often conducted using convenience sampling with a relatively small number of participants. It is important to note that in the current review, no studies addressing the link between HL and health outcomes in hypertension, were found till today, conducted in the Mediterranean area or in Southern Europe. The current article highlights the need for more specifically designed interventions and/or randomized control trials, as well as cross-sectional studies, particularly in southern Europe and in the Mediterranean area, aiming at better elucidating the possible association of HL in hypertension health outcomes, together with its underling mechanisms. The role of possible cultural differences in the interpretation of the results, should also be taken into account, when conducted studies in this field.
There is evidence that HL levels positively affect hypertension health outcomes. Given the importance of the appropriate management of hypertension, specifically designed randomized control trials and intervention trials, as well as cross-sectional studies in representative samples of the population, are needed to better elucidate the above association, particularly in the area of Southern Europe, where research in this area, is scarce.
This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “Development and pilot implementation of an educational intervention program for Health Literacy and Nutrition Literacy in Hypertension Patients: A Randomized Control Trial” (MIS: 5049028).
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