. 2021 Dec 16;11(12):e056307. doi: 10.1136/bmjopen-2021-056307

Table 3.

Detailed analyses of health literacy and medication adherence

Authors, year	Sample and setting	HL measures	MA measure	Key results	Associations between HL and MA and further outcomes
Lee et al, 2013³⁵	n=293, 65+years M=74.4 years (6.3) Patients with chronic diseases from tertiary care hospitals in Cheonan, South Korea	BHLS three questions	MMAS-4	Mean HL was 8.3 (1.9). n=120 (41.0%) patients were adherent to medication.	Significant associations between HL and MA (p=NA). Self-efficacy was strongest predictor for MA in SVM model. Other factors significantly associated with MA were number of medication types, daily pill counts, duration after diagnosis.
Lee et al, 2017³⁶	n=291, 65+years M=NA Patients with chronic diseases from tertiary care hospital in South Korea	BHLS 15 questions	MMAS-8	Mean HL was 46.61 (12.66). n=89 (30.6%) patients were highly adherent with MMAS Score of 8. Mean MA was at a medium level (M=6.32 (1.61)).	HL positively correlated with MA (r=0.25, p<0.001). HL was strongest predictor of MA in hierarchical linear regression (β=0.190, p<0.001). Other significant predictors of MA in regression were perceived health status (β=0.132, p<0.02), use of magnifying glass (β=0.166, p<0.003), assistance with medication administration (β=0.120, p<0.035).
Lu et al, 2019⁴¹	n=598 M=65.8 years (9.4) Patients with coronary heart disease from tertiary hospital in Shanghai, China	HLS-EU-Q16	MOS-SAS	HL was limited for n=444 (74.5%) and adequate for n=152 (25.5%) patients. Patients with limited HL were significantly older than those with adequate HL (p=0.003). n=505 (84.7%) patients were adherent to medication.	No significant associations between HL and MA (χ²=NA, p=0.125). No significant predictive relationship between limited HL and medication nonadherence (AOR (95% CI)=0.66 (0.39–1.11), p=0.113). Patients with limited HL compared with those with adequate HL were more likely to be nonadherent to overall heart-healthy lifestyle behaviour (AOR (95% CI)=1.69 (1.13–2.53), p=0.010), exercise (AOR (95% CI)=1.50 (1.01–2.22), p=0.046), alcohol intake control (AOR (95% CI)=2.19 (1.21–3.96), p=0.010), and stress management (AOR (95% CI)=2.09 (1.32–3.29), p=0.002).
Reading et al, 2019³⁷	n=12 159, 21+ years Age median was 72.7 and 70.1 years for adherent and nonadherent patients, respectively Ethnically diverse patients with atrial fibrillation from Northern California, USA	BHLS three questions	CARDIA (three questions)	n=9349 (76,9%) patients had adequate HL. n=771 (6.3%) patients were nonadherent to medication. Significant differences in MA between age subgroups (p<0.001).	Patients with inadequate HL were more likely to be nonadherent to medication compared with those with adequate HL (AOR (95% CI)=1.32 (1.09–1.60), p<0.01) in multivariate logistic regression model. Patients were more likely to be nonadherent to medication if physically inactive (AOR (95% CI)=1.57 (1.16–2.13), p<0.01), drinking alcohol (AOR (95% CI)=1.91 (1.51–2.43), p<0.001), having diagnosis of diabetes mellitus (AOR (95% CI)=1.22 (1.01–1.48), p<0.05), having 1–7 days of self-reported poor physical health (AOR (95% CI)=1.43 (1.17–1.75), p<0.001). Patients were less likely to be nonadherent to medication if having diagnosis of hypertension (AOR (95% CI)=0.72 (0.60–0.87), p<0.05), age between 65–74 (AOR (95% CI)=0.68 (0.55–0.83), p<0.001) and age between 75–84 (AOR (95% CI)=0.67 (0.53–0.84), p<0.001).
Saqlain et al, 2019⁴⁴	n=262, 65+years M=NA Outpatients with hypertension from tertiary healthcare centres in Islamabad, Pakistan	SILS	MMAS-4	n=98 (37.4%) patients had adequate HL. n=102 (38.9%) patients were adherent to medication.	Positive and statistically significant associations between HL and MA (χ²=24.356, p<0.001). Patients with adequate HL were more likely to be adherent to medication compared with those with inadequate HL (OR (95% CI)=3.37 (1.91–5.96), p<0.001). Other significant predictors of MA were self-reported good (OR (95% CI)=4.25 (1.45–12.44), p<0.008) and moderate (OR (95% CI)=3.54 (1.37–9.16), p<0.009) subjective health and independence in activities of daily living (OR (95% CI)=2.97 (1.15–5.85), p<0.002).
Seong et al, 2019³⁸	n=277, 65+years M=74.2 (7.2) Outpatients with atrial fibrillation undergoing antithrombotic therapy in tertiary general hospital in South Korea	BHLS three questions	Single item	HL levels (M=7.9 (3.5)) were inadequate, marginal, and adequate for 28.1%, 45.5%, and 26.4% of patients, respectively. n=139 (50.2%) patients were nonadherent to medication. Significant differences in MA between age subgroups (p<0.001).	Positive and statistically significant associations between HL and MA (χ²=22.00, p<0.001). Significant predictive relationship between marginal/ inadequate HL and medication nonadherence in univariate logistic regression analysis (OR (95% CI)=2.55 (1.29–3.90), p=0.004) but not in multivariate logistic regression analysis (OR (95% CI)=1.45 (0.79–2.64), p=0.232), where only cognitive impairment was significant predictor for medication nonadherence (OR (95% CI)=2.63 (1.42–4.85), p=0.002).
Shehadeh-Sheeny et al, 2013⁴⁵	n=303, 60+years M=71 (6.04) Female Arab patients with osteoporosis from three clinics in Israel	FCCHL	MPR	n=75 (24.8%) patients had high HL compared with n=164 (54.1%) and n=64 (21.1%) with medium and low HL, respectively. n=125 (41.3%) patients had high MA.	No significant associations between MA and HL (p=0.44). 46.7% of patients with high HL were more adherent to medication compared with 35.9% of patients with low HL. In multivariate logistic regression only self-reported income was a significant predictor of MA (OR (95% CI)=1.26 (1.01–1.58), p=0.037).
Song and Park, 2020³⁹	n=116, 65+years M=72.7 (6.1) Community-dwelling older adults in healthcare centre, South Korea	BHLS 15 questions	MMAS-8	Mean HL was 42.4 (6.6). Mean MA was at a medium level (M=4.3 (2.2)).	HL positively correlated with MA (r=0.42, p<0.001). In multiple regression analysis HL was significant predictor of MA (β=0.23, p<0.001). Other significant predictors of MA were income (β=0.35, p<0.001), number of chronic diseases (β=−0.33, p<0.001), and vision problems (β=−0.32, p<0.001).
Wannasirikul et al, 2016⁴⁶	n=600, 60–70 years M=65.3 Patients with hypertension from primary healthcare centre in Sa Kaeo Province, Thailand	FCCHL	ARMS	Mean HL was 40.0 (10.4). HL levels were inadequate, marginal, and adequate for 48.7%, 43.8%, and 7.5% of patients, respectively. MA was good for 98.3% of patients.	SEM supports causal relationship between HL, MA, and blood pressure. HL had a significantly positive direct effect on MA in SEM (β=0.08, p<0.05). Cognitive ability ((β=0.22, p<0.05) and literacy (β=0.46, p<0.05) had biggest and significantly positive direct effect on MA. Literacy (β=0.15, p<0.05) and cognitive ability (β=0.52, p<0.05) had biggest and significantly positive direct effect on HL. HL had biggest significantly negative direct effect on blood pressure level (β=-0.14, p<0.05). MA had a significantly negative direct effect on blood pressure level (β=-0.02, p<0.05). Results suggest mediator effect of HL on MA.

AOR, adjusted OR; ARMS, Adherence to Refills and Medications Scale; BHLS, Brief Health Literacy Screen; CARDIA, Coronary Artery Risk Development in Young Adults; FCCHL, Functional, Communicative, and Critical Health Literacy Questionnaire; HL, health literacy; HLS-EU-Q, European HL Survey Questionnaire; MA, medication adherence; MMAS, Morisky Medication Adherence Scale; MOS-SAS, Medical Outcomes Study Specific Adherence Scale; MPR, medication possession ratio; NA, not available/ not reported; SILS, Single Item Literacy Screener; SVM, support vector machine.