Table 3.
General characteristics of studies included in the final analysis.
| Author (Year) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/Salt Intake) |
| Delavar et al., 2020 [24] | RCT (January–March 2018) | Health Literacy for Iranian Adults (HELIA) | Good | Through block randomization, 118 older adults with uncontrolled hypertension were allocated to a control or intervention group at random. Age more than 60 years old. | Blood pressure: After Health Literacy-tailored intervention, blood pressure among the intervention group is improved; nevertheless, there was no evident difference between the groups (p > 0.05). |
| Gaffari-fam et al., 2020 [25] | Cross-sectional | HELIA | Good | 210 hypertensive patients in Iran. Age more than 30 years (Mean age was 56.7 years) | Blood pressure: The health literacy dimensions contributed to a significant increase of 4.7% for the variance in high blood pressure. |
| Costa et al., 2019 [26] | Cross-sectional | The Short Assessment of Health Literacy for Portuguese-speaking Adults (18 items) SAHLPA-18 |
Good | 392 hypertensive elderly patients. More than 60 years. | Blood pressure: Inadequate (high) blood pressure was linked to the following factor: inadequate functional health literacy. |
| Borges et al., 2019 [27] | Cross-sectional | Short Test of Functional Health Literacy in Adults (S-TOFHLA) | Good | 357 adults from basic health units in Brazil. Aged between 18 to 39 years | Blood pressure: There was a statistically significant decrease in associations evaluated (p < 0.05) when it came to hypertension and participants’ health literacy level. |
| Study, Year (References) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/Salt Intake) |
| Selcuk et al., 2018 [28] | Cross-sectional | European Health Literacy Survey Questionnaire (HLS-EU-Q) | Good | 556 hypertensive patients in Turkey. Aged 18 years and above. Mean age was 55.74 ± 13.69 years (range 18–88) | Blood pressure: According to multivariate logistic regression analysis, health illiterate patients had higher uncontrolled blood pressure (OR: 2.06, 95% CI: 1.34–2.94). |
| # Halladay et al., 2017 [22] | Cohort | STOFHLA | Fair | 493 patients with uncontrolled hypertension in rural primary care, US. The mean age was 57 (min = 20, max = 92) years. | Blood pressure: There were statistically significant reductions in mean Systolic Blood Pressure (SBP) in both the low and high health literacy groups (6.6 and 5.3 mmHg, respectively) after a year, however, there was no significant difference between the groups (Δ 1.3 mmHg, p = 0.067). The low and high health literacy groups both reported lower blood pressure in 2 years by 8.1 and 4.6 mm Hg, respectively, with no significant between-group difference (Δ 3.5 mm Hg, p = 0.25). |
| Study, Year (References) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/Salt Intake) |
| # Shi et al., 2017 [23] | Cohort | Chinese health literacy scale for hypertension (CHLSH) | Poor | 360 hypertensive patients in China. The age range of participants was 31–88 years. | Blood pressure: Low health literacy indicates high SBP. The rate of hypertension control increased as the CHLSH score increased (p < 0.001). The findings show that for three-quarters of the year, patients in the high literacy group have better SBP management than those in the low literacy group. |
| Hu et al., 2017 [29] | Cross-sectional | Health Literacy Scale for Hypertension | Good | 596 hypertensive patients in China | Blood pressure: Blood pressure control was linked to total health literacy (z = 2.493, p = 0.013), ability to comprehend pictures (z = 3.187, p = 0.001), and accessing health-related information (z = 3.274, p = 0.001). |
| Yilmazel and Centikaya, 2017 [30] | Cross-sectional | Newest Vital Sign Scale and Blood Pressure Concept Test (adapted from REALM) | Good | 500 volunteer teachers aged 35–49. The mean age of the study group was 42.91 ± 8.75 and in the hypertensive subjects, 48.35 ± 7.53. | Blood pressure: Health literacy was shown to be insignificant when it came to hypertension awareness and control.Knowledge: Those with hypertension who were aware of the disease had a higher health literacy level than those who were not (p > 0.05). |
| Study, Year (References) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/Salt Intake) |
| Hall et al., 2016 [31] | Cross-sectional | SAHLSA (Short Assessment of Health Literacy for Spanish-Speaking Adults) | Good | 45 Latino Migrant and Seasonal Farmworkers. Ages ranged from 29 to 60 | Blood pressure: Higher levels of acculturation and health literacy were linked to improved blood pressure control (p = 0.01). |
| Wannasirikul et al., 2016 [32] | Cross-sectional | Adopted from Ishikawa et al. (2008) | Good | 600 aged 60 to 70 years with a mean age of 65.3 years for hypertensive patients in Primary Health Care Centres in Thailand | Blood pressure: Blood pressure is strongly linked with health literacy (β = −0.14, p < 0.05). |
| Glashen, 2015 [33] | Cross-sectional | STOFHLA | Good | 136 hypertensive Latino adults in the US aged 18 to 49 years | Blood pressure: Health literacy and hypertension association were not statistically significant (χ2 (1) = 0.811, p = 0.368). |
| McNaughton et al., 2014 [34] | Cross-sectional evaluation between 1 November 2010 and 30 April 2012 | Brief Health Literacy Screen (BHLS) | Good | 46,263 hospitalizations were available for analysis. Aged 18 years or older | Blood pressure: Low health literacy indicates extreme high blood pressure (aOR 1.08, 95% confidence CI 1.01, 1.16) and high blood pressure in people who had never been diagnosed with hypertension (OR 1.09, 95% CI 1.02, 1.16). Such associations were not found among patients with low health literacy and diagnosed hypertension. |
| McNaughton et al., 2014 [35] | Cross-sectional | The Rapid Estimate of Adult Literacy in Medicine (REALM) | Good | 423 urban hypertensive patients with coronary disease in the US | Blood pressure: Limited health literacy indicates uncontrolled blood pressure (OR 1.75, 95% CI 1.06–2.87). |
| Study, Year (References) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/Salt Intake) |
| Ko et al., 2013 [36] | Cross-sectional | STOFHLA Singapore | Good | 306 hypertensive patients in the primary clinic in Singapore | Blood pressure: The degree of health literacy did not affect achieving the target blood pressure (p = 0.71). Knowledge: Higher health literacy level indicates higher hypertension knowledge scores (p < 0.001). |
| Willens et al., 2013 [37] | Cross-sectional | BHLS | Good | 10644 hypertensive patients aged more than 18 years | Blood pressure: Health literate patients had a slightly lower odds of having their hypertension under control. |
| Aboumatar et al., 2013 [38] | Cross-sectional | REALM | Good | 275 hypertensive patients in the US | Blood pressure: Patients with limited literacy reported poorer blood pressure management at the baseline. |
| Lenahan et al., 2013 [39] | Cross-sectional | TOFHLA | Good | 215 hypertensive patients in the United States with an average age of 60 years old (SD = 8.0 years) | Blood pressure: Uncontrolled blood pressure (p = 0.03) and medication identification (p = 0.001) were both associated with health literacy. |
| Shibuya et al., 2011 [40] | Cross-sectional | Chinese Health Literacy (CHL) | Good | 320 Middle-aged participants in an urban clinic, Japan (53 to 57 years) with an average age of 54.4 years old | Blood pressure: Limited health literacy and hypertension knowledge indicate poor health and raised blood pressure |
| Study, Year (References) | Design | Instrument | Quality Score | Study Sample | Outcomes (Blood Pressure/Knowledge/ Salt Intake) |
| Suon and Ruaisungnoen, 2019 [41] | Cross-sectional | Health Literacy Sodium Restriction (HL-SR) | Good | 317 hypertensive patients in Cambodia. Age (21–72 years old) with average age of 54 years (SD = 8.95) | Salt Intake: Literacy skills (β = 0.125, p = 0.019), knowledge of hypertension and sodium restriction (β = 0.266, p < 0.001), and health professional communication (β = 0.359, p < 0.001) were reported to be strongly associated to Health Literacy-Sodium Restriction. |
| Luta et al., 2018 [3] | Cross-sectional | European Health Literacy Survey Questionnaire 47-item (HLS-EU-Q47) |
Good | 141 workplace population in Switzerland. Ages of 15 and 65 | Salt Intake: The health literacy index and food literacy score did not have a significant relationship with salt intake (24 h urine), however, the awareness variable “salt content impacts food/menu choice” did. |
| Hutchison et al., 2014 [42] | Cross-sectional | Newest Vital Sign | Good | 250 hypertensive patients in primary clinical care in the US. Age from 30 to 85 years (with an average age of 55 years). | Salt Intake: Adequate health literacy indicates a higher chance of adhering to the low salt plus diet (OR = 1.18, 95% CI: 0.50–2.79) than those with limited health literacy, but the results were not significant. |
SD = standard deviation. # Studies that were excluded from synthesis.