The impact of health literacy interventions on glycemic control and self‐management outcomes among type 2 diabetes mellitus: A systematic review

Abstract Diabetes imposes an increasing health and economic burden on individuals living with it and their societies worldwide. Glycemic control is necessary to reduce morbidity and mortality of type 2 diabetes mellitus (T2DM). Self‐management is the primary tool for managing diabetes. Health literacy (HL) is the primary driver of self‐management activities. The aim of this review is to evaluate the impact of HL interventions on glycemic control and self‐management outcomes among T2DM. MEDLINE, CINAHL, PubMed, Cochrane, Scopus, and Web of Science were searched for eligible papers. Fifteen randomized controlled trials published in English between 1997 and 2021, used HL‐driven intervention, and measured the level of glycohemoglobin A1c (HbA1c) and self‐management of T2DM patients were included in this review. The findings showed that HL‐driven intervention had a positive impact on glycemic control and improved self‐management behaviors. The level of glycemic control and self‐management skills were improved through individual and telephone‐based intervention respectively. Community worker‐led interventions were effective in improvements in diabetes knowledge and self‐care behaviors; however, nurse‐led interventions were effective in glycemic control. Better glycemic control is achieved in hospital settings compared to outpatient settings. HL interventions yielded better improvement in self‐management among people with longer diabetes duration (more than 7 years). It was possible to achieve a large reduction in HbA1c level after a 3‐month intervention in hospital settings. HL‐driven interventions are effective in glycemic and diabetes self‐management outcomes.

• The level of glycemic control and self-management skills were improved better through individual and telephone-based intervention, respectively, in comparing group intervention.
• Community worker led interventions were effective in improvements in diabetes knowledge and self-care behaviors; however, nurse-led interventions were more effective in glycemic control.
• Better glycemic control was achieved in hospital settings compared with outpatient settings.
• HL interventions yielded better improvement in self-management among people with a longer diabetes duration (more than 7 years) than those with short duration of diabetes.
• It was possible to achieve a significant reduction in HbA1c level after a 3-month intervention in hospital settings.

| INTRODUCTION
Diabetes imposes an increasing health and economic burden on individuals living with it and for their societies worldwide.There were 537 million people living with all types of diabetes in 2021 and this number is predicted to increase to 643 million and 783 million by 2030 and 2045 respectively. 1Type 2 diabetes mellitus (T2DM), which accounts for 98.3% of diabetes cases, 2 is a complex metabolic disorder characterized by insulin resistance and pancreatic beta-cell dysfunction. 3Hyperglycemia caused by T2DM often leads to various microvascular (eg, retinopathy, neuropathy, nephropathy) and macrovascular (coronary artery disease, cerebrovascular disease) complications. 4 Diabetes is a global health concern that has a significant impact on society and the economy.It results in increased medical expenses, premature death, decreased productivity, and lower quality of life. 5According to the American Diabetes Association, the overall expenses associated with diabetes have risen from $245 billion in 2012 to $327 billion in 2017, representing a 26% increase over a five-year period.Individuals with diabetes have medical expenditures that are roughly twice as high as those without diabetes. 6In 2021, diabetes resulted in health expenditures of at least US$966 billion globally, reflecting a 316% increase over the last 15 years. 1 Complications related to diabetes in the lower extremities are a significant and expanding source of disability across the globe. 7n addition to the morbidity of diabetes it is one of the leading causes of mortality worldwide; for instance, globally, there was a 5% increase in premature mortality due to diabetes between 2000 and 2016. 8The number of deaths worldwide related to diabetes has risen sharply from 1.5 million in 2012 9 to 6.7 million in 2021. 1 Glycemic control is necessary to reduce morbidity and mortality of T2DM.According to a diabetes control and complications trial, normalization glycohemoglobin A1c (HbA1c < 7%) is associated with prevention of diabetes complications such as neuropathy, retinopathy, and nephropathy. 10Each 1% reduction in HbA1c decreases the risk of microvascular complications by 37%, deaths related to diabetes by 21% and myocardial infarction by 14%. 11Reducing the HbA1c level by 1% is associated with a 13% decrease in diabetes-related total health care costs. 12Glycemic control is also the most important behavioral and therapeutic goal in diabetes care. 13Selfmanagement is the primary tool for managing diabetes 14 and the aim of diabetes self-management is to control blood glucose and reduce the risk of diabetes-related complications. 15diabetes self-management involves a collaborative effort by health care providers and patients in which individuals with diabetes acquire the necessary knowledge and abilities to make behavioral adjustments that help them manage the disease. 16Diabetes self-management focuses on healthy eating, physical activity, monitoring blood sugar, medication adherence, problem-solving, and healthy coping mechanisms. 17Self-management interventions are associated with improving glycemic control, quality of life, and diabetic complications. 18ealth literacy (HL) is the primary driver of selfmanagement activities.HL is the capacity to read, understand, make decisions, and take actions that affect health status. 19Low HL has been linked to several negative health outcomes, such as poorer overall health, higher hospitalization and mortality rates, reduced ability to manage chronic illnesses, and increased patient expenses.Individuals with appropriate HL levels are more likely to use available health services and make well-versed health decisions. 20Low HL is a major barrier to the development of self-management skills. 21Further, HL is associated with confidence in self-managing diabetes. 22The low level of HL about the importance of controlling blood glucose is the key barrier to diabetes self-management. 23here is increasing evidence demonstrating a strong association of HL with diabetes knowledge; however, little is known about the effectiveness of HL-driven interventions specific to T2DM self-management and glycemic control.This systematic review aims to address this gap by assessing the effectiveness of HL intervention on glycemic control (HbA1c) and T2DM self-management using randomized controlled trials (RCTs).

| Search strategy
To identify HL-driven T2DM self-management interventions focusing on glycemic control, we searched six databases including MEDLINE, CINAHL, PubMed, Cochrane, Scopus, and Web of Science.Search terms included "health literacy," "diabetes mellitus type 2," "self-management," "glucose control," and "clinical trials" (see Box 1).
The protocol of this systematic review is registered in PROSPERO (International Prospective Register of Systematic Reviews) (CRD42022348050).The systematic review was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines (see Figure 1).Initial search identified 817 studies through the six databases searched.After excluding the duplications of 564 articles and title and abstract screening, 40 articles were eligible for full-text screening.The 40 papers were assessed against the inclusion criteria (criteria listed further in the next section) and 15 articles were included in the review.
The quality of each study was assessed independently by two authors (Jamila Butayeva, Zubair Ahmed Ratan) using the critical appraisal checklist tool developed by Joanna Briggs Institute (JBI) This tool is the most coherent and sensitive tool for validity, with its focus on congruity. 24The JBI critical appraisal tool is a widely accepted method for evaluating the methodological quality of studies. 25All the disagreements were resolved by discussion with the senior researcher (Hassan Hosseinzadeh).The JBI score was calculated for each study.A JBI score of 70%-100% was considered as high quality, a score of 69%-50% was considered moderate quality, and <49% was considered low quality.Overall mean score for quality was 80.9% (see Figure 2).

| Inclusion and exclusion criteria
Only HL-driven RCTs published in English and conducted among T2DM patients aged over 18 years were included in this review.Eligible studies had to report both glycemic control and self-management outcomes and use a HL-driven intervention.Trials with a minimum sample size of 100 and an intervention duration of >3 months were included.This is because RCTs using smaller samples and shorter intervention delivery time were seen as a threat to the validity and generalizability of research results. 26X 1 Example of search strategy for review.

| General study description
All of the 15 selected articles were published in English between 1997 and 2021.Five of them were conducted in developed countries including 2 in the United States, 27,28 2 in England, 29,30 1 in Sweden, 31 and 10 in developing countries including 4 in Brazil, [32][33][34][35] 3 in China, [36][37][38] 1 in Ethiopia, 39 1 in Nigeria, 40 and 1 in Vietnam 41 (see Figure 3).Three studies were conducted in hospital settings 36,37,41 and the rest were conducted in outpatient clinics, diabetes clinics, primary health care, or community health centers (see Table 1).From selected articles three were three-arm RCTs 28,33,34 and the rest were twoarm RCTs.

| Patients' characteristics
Overall, 3556 participants were included in the selected studies.The proportion of men and women varied across trials but most of the participants (55%) were female.The sample size ranged from 101 to 623 participants.The participants' age ranged between 18 and 85 years old (see Table 1).

| Description of interventions
Included studies were heterogeneous in terms of type of intervention, diabetes population, and outcomes assessed.
Interventions varied in terms of the type of intervention programs, duration of program, follow-up period, and intervention providers.4][35] The long follow-up period of 12 months was performed in four studies, 31,33,34,38 and 6-month follow-up was performed in five studies. 29,30,32,36,37In eight studies, interventions were delivered by a nurse, 28,31,32,[34][35][36]39,40 in two studies interventions were delivered by a diabetes educator, 37,38 in two studies interventions were delivered by a community worker, 29,30 in one study the intervention was delivered by a support professional, 33 in one study the intervention was delivered a peer educator, 27 and in one study the intervention was delivered by a medical doctor. 41 Th most common method of intervention delivery was group education.27,[29][30][31][37][38][39][40][41] In three studies, a combination of group and individual education, 28,32,36 group education and telephone calls, 34 and group education and home visits 33 were used.In one study, a combination of group education, home visit, and telephone calls was used.35 F I G U R E 2 Evaluation of the quality of articles using Joanna Briggs Institute (JBI) tool.

| Main findings
The selected studies focused on several outcomes, but we concentrated only on HbA1c and self-management outcomes (see Table 2).

| Glycemic control (HbA1c)
All studies evaluated the effect of a HL-driven intervention on HbA1c; 14 studies showed that HL had a significant and positive impact on HbA1c control and 1 study did not find any significant changes in HbA1c level after a HL intervention program. 31The largest reduction in HbA1c level (3.4%) was achieved after a 3-month nurseled individual intervention with a 6-month follow-up in a hospital setting. 36Diabetes education intervention delivered by a nurse in an outpatient setting was more effective in reducing HbA1c (1.5% reduction) among more educated participants. 32Female and educated participants as well as those who participated in more educational sessions had better results in glycemic control in outpatient settings. 27,30,38Similarly, educated women and participants who had higher levels of HbA1c at the baseline were more likely to have better improvements in HbA1c in outpatient settings. 28,29,39Participants from urban area and those with low body mass index (BMI) levels demonstrated substantially lower outcomes in HbA1c level in outpatient settings. 27,32,35,39Surprisingly, participants who did not have any occupation were more likely to have a better glycemic control after long intervention periods of 12 months [33][34][35] and 7 months. 37HLdriven interventions were also more effective in HbA1c control among people who had comorbidities and low levels of alcohol consumption. 28,34,37,41

| Diabetes self-management
38,41 Of them, five evaluated diabetes knowledge, [29][30][31][32]41 and all of them found a positive correlation between HL interventions and diabetes knowledge. Intrventions delivered by community workers compared to those delivered other providers were more likely to improve diabetes knowledge among educated women.29 Nurse-led intervention using group education with a 6-month follow-up delivered in outpatient settings resulted in a greater increased diabetes knowledge compared to tailored education interventions.35 Nine articles evaluated the impact of HL on self-management.2 Patients with longer disease duration and those received an intervention through home visits achieved better self-care adherence.28,29,33,38 A telephone intervention with a 12-month diabetes empowerment program delivered by a nurse was more likely to result in a better self-care practice than group education.34 Regardless of the type and setting of the interventions, better HL improved self-care behaviors including being physically active, problem-solving skills, healthy coping strategies, quality of life, satisfaction with daily life, and managing hyperglycemia in the intervention groups compared to control groups.[28][29][30]38 Educated women showed better results in managing hyperglycemia and regular glucose checks after 6-month community worker-delivered intervention in diabetes clinics compared to noneducated women.29,30 Physical activity level and adherence to a healthy diet were more likely to increase in the intervention group compared to

| DISCUSSION
Our systematic review of 15 included articles showed that HL intervention was effective in glycemic control and improving diabetes knowledge and self-management skills among diabetes patients.Fourteen out of 15 included RCTs showed that HL interventions resulted in significant improvements in HbA1c levels.However, HL-driven interventions delivered through individual education at hospital settings were more effective in decreasing uncontrolled levels of HbA1c compared to HL-driven interventions delivered using group education.This might be due to tailored education and physical proximity to health care services at the hospitals, which might facilitate the impact of HL interventions. 42Literature suggests that tailored education based on patient needs motivated them to adhere to life adjustment measures. 43In line with a recent systematic review, 44 our findings showed that HL interventions resulted in more improvements in HbA1c levels among patients with suboptimal glucose levels where the baseline mean of HbA1c was >9%. 28,29,39This finding suggests that T2DM patients with poorly controlled HbA1c levels are more likely to benefit from HL intervention. 45There was a positive relationship between the amount of time participants spent on education sessions during HL education intervention and improvement in glycemic control.In other words, in line with a recent systematic review, 46 participants who engaged more with HL interventions achieved more improvements in glycemic control.Our findings showed that nurse-led interventions were associated with better glycemic control, 28,32,[34][35][36]39,40 which may be explained by the fact that practice nurses are capable of dealing with complicated health problems and can give information and support to patients and their families efficiently, which are essential in empowering patients to adopt new behavior. 47 Ou review highlights that after participating in a 3-month peer-education program, individuals in urban areas are more likely to achieve better glycemic control compared to those in rural areas.39 This might be explained by the literature suggesting that people residing in rural areas tend to perceive ill health and mortality as natural phenomena, whereas individuals living in urban areas are less accepting of ill health and more likely to seek health care advice.48 There was also a positive linear correlation between BMI and HbA1c levels and participants with higher BMI index had higher level of HbA1c.
Participants with low BMI level had lower HbA1c level after interventions in some studies. 27,32This is consistent with previous literature, which showed that BMI is a significant predictor of poor HbA1c control 49 and the increase in BMI levels leads to rising in insulin levels resulting in increasing HbA1c levels. 5031][32]41 HL interventions resulted in a greater impartment in diabetes knowledge when it was delivered by community workers compared other health care providers, which is in line with the findings of a recent systematic review showing that HL interventions were positively correlated with diabetes knowledge and glycemic control. 51This might be explained by the fact that community workers are more likely to share similar cultural, linguistic, and socioeconomic backgrounds with patients, which are essential for providing interventions meeting real-world needs. 52Our findings also showed that more educated women were more likely to achieve greater impartments in diabetes knowledge when HL interventions were delivered by community workers compared to noneducated women.Similarly, a recent study showed that patients with high literacy level were 1.85 times more likely to gain diabetes knowledge required to manage their diabetes compared to their less educated counterparts. 53This might be because highly educated people are most likely to understand the salience of health information and are more capable to put new information in practice. 54even out of nine RCTs that assessed diabetes selfmanagement found that HL interventions were linked to improved self-management outcomes [28][29][30]33,34,37,38 such as physical activity, healthy diet, diabetes knowledge, problem-solving, and quality of life. We found tht that telephone-based HL interventions among patients with a longer diabetes duration were more likely to yield positive improvements in self-management behaviors especially among less educated participants compared to face-to face group education.33,34 This might be because telephone-based interventions may aid less educated people to understand the context of education and give them more chances to ask questions and seek support.Surprisingly, intervention delivered through home visits among patients who had longer diabetes duration were effective in improving self-management outcomes.28,29,33,38 According to literature home visits allow health professionals to see patients' living conditions and involve family members and caregivers in health education, which are critical in gaining better improvements in behavior change interventions.55 The reason for the patients with a longer diabetes duration responding well to HL interventions might be because they are more likely to experience the consequences of uncontrolled diabetes, which might motivate them to engage well in HL interventions.

| LIMITATIONS
This study offers invaluable information about the impacts of HL intervention on glycemic control and diabetes self-management outcomes; however, it has some limitations.Only studies published in English were included in this review, which might lead to the exclusion of high-quality studies published in other languages.Most of the selected studies were conducted in developed countries, which may limit the generalization of the findings of this review to patients living in developing countries.The heterogeneity of study settings, intervention strategies used, and study participants' socioeconomic characteristics make generalization of the findings to similar populations difficult.A lack of information about the professional background of those who delivered the interventions could affect the quality of the information delivered during the interventions.Using different outcome measures and tools made analysis difficult.The study outcomes were presented for less than 1 year so long-term effects could not be examined.Only RCTs were included in this review, which might limit the generalizability of these findings to real-world settings.

2 F I G U R E 1
Flow chart of study search and selection of selected papers.

1 F
I G U R E 3 Global map indicating countries where selected studies were conducted.TA B L E 1 Demographic (age, gender) and intervention (settings, program, length, and follow up time) characteristics.

Findings from our review of 15
articles suggests group and telephone-based HL interventions and interventions delivered by nurses and/or community workers and interventions in hospital settings yield promising outcomes in glycemic control and self-management, even after a short duration.Overall, HL-driven interventions are effective in glycemic and diabetes self-management outcomes.50.Agrawal N, Agrawal MK, Kumari T, Kumar S. Correlation between body mass index and blood glucose levels in Jharkhand population.Int J Contemp Med Res.2017;4(8):1633-1636. 51.Alharbi ER, Sofar SM, Wazqar DY.Effect of health educational guidelines on self-management practices among patients with chronic obstructive pulmonary disease: a scoping review.Evid Based Nurs Res.2022;4(4):55-68.52.Han H-R, Kim K, Murphy J, et al.Community health worker interventions to promote psychosocial outcomes among people living with HIV-A systematic review.PLoS One.2018;13(4): e0194928.53.Tefera YG, Gebresillassie BM, Emiru YK, et al.Diabetic health literacy and its association with glycemic control among adult patients with type 2 diabetes mellitus attending the outpatient clinic of a university hospital in Ethiopia.PLoS One.2020;15(4):e0231291. 54.Shankar J, Ip E, Khalema E, et al.Education as a social determinant of health: issues facing indigenous and visible minority students in postsecondary education in Western Canada.Int J Environ Res Public Health.2013;10(9):3908-3929. 55.Liang Y-H, Wang KH, Huang HM, Shia BC, Chan SY, Ho CW.Reducing medication problems among minority individuals with low socioeconomic status through pharmacist home visits.Int J Environ Res Public Health.2022;19(7):4234.How to cite this article: Butayeva J, Ratan ZA, Downie S, Hosseinzadeh H.The impact of health literacy interventions on glycemic control and selfmanagement outcomes among type 2 diabetes mellitus: A systematic review.Journal of Diabetes.2023;15(9):724-735.doi:10.1111/1753-0407.13436 Main outcomes including HbA1c and self-management behaviors among the selected studies.
T A B L E 1 (Continued) Abbreviations: CM, conversation map; DSME, diabetes self-management education.TA B L E 2