Determinants of Poor Treatment Adherence among Patients with Type 2 Diabetes and Limited Health Literacy: A Scoping Review

Prevention of complications and successful control of diabetes require preventive and therapeutic measures. Patients' nonadherence to medication and diet regimens and healthcare protocols is associated with significant therapeutic and economic consequences. The present scoping review aims to identify determinants of poor treatment adherence among patients with type 2 diabetes and limited health literacy in 2021. This scoping review was conducted in five stages: designing a research question, searching and extracting related studies, selecting related studies, tabulating information, and reporting results. Data were collected from six foreign electronic databases (Embase, Science Direct, PubMed, Google Scholar, Scopus, and Web of Science) and four Iranian electronic databases (MagIran, SID, IranDoc, and IranMedex) using keywords “Type 2 diabetes”, “barriers”, “treatment”, “medication”, “adherence”, “non-adherence”, “limited adherence”, and “limited health literacy” from January 2010 to November 2021. From an initial 146 articles, 18 articles were eligible for review. Eighteen studies involving 3925 patients with T2DM from eight countries were included. The prevalence of nonadherence ranged from 42% to 74.3%. Barriers to treatment adherence, which were common among the articles, included economic problems, poor communication with healthcare team, lack of family support, lack of knowledge, misconceptions, and limited health literacy. The results of the present study provided modifiable and nonmodifiable factors affecting treatment adherence among patients with type 2 diabetes. Modifiable factors are essential by performing appropriate interventions with the target group and health professionals.


Introduction
According to the World Health Organization (WHO), approximately 422 million people worldwide suffer from diabetes, with the Eastern Mediterranean countries having the highest prevalence (43 million) [1]. The International Diabetes Federation predicts that the prevalence of type 2 diabetes in Iran will increase from 9.6% in 2019 to 10.6% in 2030 and 11.1% in 2045 [2]. Treatment adherence refers to prevention of complications and successful control of diabetes, which are possible only with the active participation of patients in their treatment plans as recommended by their healthcare providers [3]. The definition of adherence in chronic conditions, as given by the WHO, is behaviors such as taking medications, following a diet, living a healthy lifestyle that correspond with recommendations of healthcare providers [4]. Treatment adherence has become a major challenge for medical professionals and social scientists. Efforts by physicians and healthcare professionals to ensure that patients adhere to medication regimens have frequently proven ineffective [5]. While some programs are aimed at increasing treatment adherence have been successful, it appears that approximately half of them have failed [6]. Patients' nonadherence to medication and diet regimens has significant economic and therapeutic consequences. For example, patients who do not adhere to medication are at risk for complications that compromise their health and severely affect their overall quality of life [7]. Treatment nonadherence has a negative influence on patients and results in the disease progressing and becoming more chronic throughout the world, so chronically ill patients need more treatment adherence [8].
Nonadherence to medication regimen is a complex behavioral process and is affected by several factors such as patients' characteristics, physician-patient interaction, and healthcare system [4]. The World Health Organization has divided the various factors affecting medication nonadherence into five categories: social and economic factors, healthcare team-and system-related factors, conditionrelated factors, therapy-related factors, and patient-related factors. Although some of these factors are unchangeable, patient-related factors can be changed by training and increasing their knowledge [9].
Health literacy is one of the variables affecting patients' knowledge of their disease [10]. Health literacy includes reading, listening, analytical, decision-making skills, and the ability to apply them to health situations [11]. The World Health Organization has identified health literacy as one of the biggest determinants of health. It has also recommended the countries around world to establish an association consisting of all affected people to monitor and coordinate strategic activities regarding the health promotion in different communities [12].
Many unpleasant health-related consequences occur because of poor health literacy. Limited health literacy has been associated with poor health outcomes, detrimental health behaviors, lower patient satisfaction, and in some cases, higher mortality [13]. Individuals with limited health literacy have trouble understanding the oral and written information provided by physicians, nurses, and insurers, as well as medication instructions, so they cannot achieve the health services they need in healthcare systems. These individuals have little knowledge about healthcare conditions and use less preventive services [14]. Studies show that health literacy is one of the factors influencing treatment adherence among patients with diabetes [15][16][17]. Limited health literacy is very common among patients with diabetes, which is associated with poor awareness and less understanding of diabetes as well as outcomes such as retinopathy and poor blood sugar control [18]. A practical intervention can improve knowledge, skills, attitudes, values, and behaviors. Education, by increasing knowledge and information, can create the necessary skills to achieve goals [19].
Many studies have examined the barriers to treatment adherence from different dimensions and with different inclusion criteria, so summarizing the findings of these studies can provide appropriate and correct strategies to increase treatment adherence among patients with type 2 diabetes. Therefore, the present study is aimed at reviewing the factors affecting the poor treatment adherence among patients with type 2 diabetes and limited health literacy in 2021. In addition, interventions can be designed, implemented, and evaluated to take an effective step in improving the health and quality of life of these patients.

Materials and Methods
This scoping review includes five stages including designing a research question, searching and extracting related studies, selecting related studies tabulating, and summarizing information and data and reporting results [20].
After the research question was designed (what factors affect the poor treatment adherence among patients with type 2 diabetes and limited health literacy?), a search strategy was developed, inclusion criteria were determined for selected studies, data extraction forms were prepared, and the data analysis program was identified.
2.1. Information Resources and Searches. The researcher searched Iranian (MagIran, SID, IranDoc, and IranMedex) and foreign databases (Embase, Science Direct, PubMed, Google Scholar, Scopus, and Web of Science) from 25 October 2021 to 14 November 2021. The search keywords were "Type 2 diabetes", "barriers", "treatment", "medication", "adherence", "non-adherence", "limited adherence", and "limited health literacy". Persian language databases were also searched. The definition of HL used in this review was developed by Kooshyar et al. [21]. This definition includes concepts such as numeracy, health education, health promotion, patient understanding, and comprehension. Moreover, the definition of treatment adherence developed by Mehrtak et.al was used in this review [22]. This definition includes concepts such as medication, diet, and lifestyle adjustments in accordance with the recommendations accepted by health care personnel.
In this study, the publication bias, source, and geography were investigated. In this study, these biases have not been done.

Inclusion and Exclusion
Criteria. All qualitative, crosssectional, descriptive-analytical, systematic, trial, and review articles addressed at least one of the factors influencing low treatment adherence from the perspective of patients, their families, or healthcare providers; the full texts of articles related to limited health literacy, which were published in valid journals from January 2010 to November 2021, were among inclusion criteria. Articles that did not specifically address the factors affecting treatment adherence among patients with diabetes and studies conducted before January 2010 were excluded.

Selection of Related Studies.
Totally, 146 articles were obtained using the above keywords. Endnote was used to organize the studies. Duplicate studies were excluded. Then, after the titles and abstracts were reviewed, noneligible studies were eliminated. Therefore, the full texts of 63 studies were studied. At this stage, 45 articles were deleted, and finally, 18 articles published from 2013 to 2021 were selected and reviewed.
Data were extracted using a standard form and included the following categories: study IDs (study author and year of publication), location, study population, study type, sample size, main aims, materials and methods, theoretical approaches, results, and conclusions.

Results
Eighteen studies involving 3925 patients with T2DM from eight countries were included.
Measures of treatment adherence in these studies According to the results of the study, four main areas of economic problems, poor communication of healthcare team, socioindividual factors, and limited health literacy were mentioned as barriers to treatment adherence (Table 1).
(1) Economic problems Studies have shown that financial problems are among the barriers to adherence to treatment. Adherence to a proper diet, physical activity, medication, blood sugar measurement, blood glucose meter (glucometer), and proper foot care is costly; and financial problems lead to the waiver of some self-care behaviors. Medical costs are a deterrent to continuing treatment in patients with diabetes, especially for patients with low economic status and patients without health insurance coverage [4,23,24].
(2) Poor communication of healthcare team Poor communication of healthcare team was another factor in the treatment nonadherence among patients with diabetes. The results of the present study showed that the physician did not pay attention to the patient's words and did not behave well with patients. As patients cannot communicate continuously and usefully with their doctors, they stop continuing to see a doctor or reduce the number of their visits. Patients need counselling and interaction with the healthcare team, the necessary recommendations for disease management and motivation to adhere to the treatment [3]. Sometimes, doctors' improper behavior and attitude make patients unmotivated, so they stop their treatment. Therefore, the practice of the healthcare team is one of the most important factors in adhering to treatment among patients with diabetes. According to these results, training of communication techniques, especially effective listening skills, will play an effective role in this regard [25].

(3) Socioindividual factors
According to the findings of studies, some individual and social factors can play a role in adherence to treatment. These factors include patients' negative perceptions about the disease; worries about the side effects of drugs; lack of support from family, peers, and society; cultural and religious beliefs; inability to take drugs on a regular basis; forgetting doses; and experiencing drug side effects and disease [23,24,26]. Age and level of education were also mentioned as factors affecting treatment adherence [4].

(4) Limited health literacy
According to studies, although adherence to treatment is the most appropriate way to control type 2 diabetes, limited health literacy is an important barrier to patients' adherence to treatment instructions. Studies have shown that the level of health literacy in patients with type 2 diabetes is mostly low, and it is necessary to increase the level of health literacy in these patients by using strategies such as simplifying information or using simple and understandable training [21,22]. Table 2 shows the full information of the articles and their results.
The study flowchart is shown in Figure 1.

Discussion
The articles presented in this scoping review show modifiable and nonmodifiable factors affecting poor treatment adherence among patients with diabetes. Disbelief in the physicians' and healthcare providers' prescriptions; misconceptions about medications and diets; lack of support of family, peers, and community; complex treatment regimens; poor healthcare system; poor information and knowledge, concern, fear, discomfort, fatigue, and burnout; prioritization of other family members; poor working conditions; the healthcare team's poor practice, low self-efficacy, depression, multiple drug use, and low health literacy are among the modifiable factors affecting poor treatment adherence     Journal of Diabetes Research among patients with type 2 diabetes. According to the results of studies, the patient's dissatisfaction with working condition as well as reaction, behavior, and support of others and family prevents them from the treatment adherence [23,34]. In addition, not following the diet due to poor working conditions, not having enough time to eat at workplace, having difficulty in treatment compliance due to the type of job, and forgetting to take medication due to high workload and stress are among the factors that prevent treatment adherence among patients [38]. Various studies considered the importance of others' support from such patients. Family members play an important role in patients' treatment adherence without whom adherence to the treatment regimen would be difficult and sometimes impossible [39]. Additionally, fear of judgment, compassionate behavior of others, and blaming the patient for the disease are factors that lead to poor treatment adherence among patients [38]. According to these results, the health care team's poor practice and patients' inability to communicate with health care providers are other barriers to adherence to treatment. Health care providers are unable to facilitate treatment adherence among patients with diabetes. They focus more on patients' clinical care and treatment, less on education and counselling, and do not have enough time to listen to patients' problems and train patients and their families, while patients demand a coordinated care or healthcare interactions, which are accompanied by discussion and understanding. Clinical decisions should be participatory, taking into account the individual preferences of patients and providing alternative treatment options to them. Other studies mentioned lack of training and counselling as one of the major barriers to diabetes management [3,23,27,32]. Healthcare providers should simplify the treatment regimen (for example, reducing the number of times receiving medications on a day), negotiate with the patient about the priorities of the treatment regimen, remind care and appointments with follow-up programs, organize a care plan, design realistic goals in order to increase patients' cooperation and reduce the experience of failure, and encourage and reward the patient and family members to follow the treatment regimen or design appropriate rules in medical centres. In addition, patients should become familiar with diabetes associations or charities for their training [3].
The studies mentioned limited health literacy as an important barrier to treatment adherence. Health literacy is not simply the ability to read, rather it requires a complex group of reading, listening, analytical, and decision-making skills and the ability to apply these skills to health situations [40]. Health literacy helps a patient read, understand, recall, and follow health instructions [24]. High level of health literacy delays the disease complications, which is why health literacy can change behavior and lifestyle and promote health [41]. Ahmad et al. showed that for every one percent decrease in knowledge about the disease, treatment nonadherence had a 3.6-point increase [42]. Although treatment adherence is the most appropriate way to control type 2  (7) financial problems.
All articles obtained from databases = 146 Remained articles after reviewing the titles and abstracts = 63 Eligible articles = 57 Articles excluded after their full texts were studied = 26 Articles eligible for writing a review article = 18   [21,26,29,33]. As a result, inadequate health literacy among these patients is a warning signal to health officials and policy makers and health care providers. Therefore, health promotion programs should pay more attention to health literacy. To increase health literacy, in addition to using simple and understandable educational materials, health education professionals' help is an effective measure to improve health literacy among patients with type 2 diabetes [22].
Some factors affecting treatment adherence among patients with diabetes can be modified by training and empowering patients and their families while some others by training healthcare providers, so the impact of these factors should be considered when designing educational interventions.
Nonmodifiable factors include economic problems, lack of insulin, age, education, cultural and religious beliefs, and the experience of some drug side effects. According to the results of the articles, financial problems have a major contribution to low treatment adherence among patients with diabetes. Following a proper diet and exercise, preparing medication, measuring blood sugar, preparing glucometer, and providing proper foot care are costly, so financial problems lead to the prevention of some self-care behaviors [24]. Healthcare costs are a deterrent to treatment adherence among patients with diabetes, especially patients with low socioeconomic status and patients without health insurance coverage [30]. According to the New Mexico Diabetes Prevention Program, low annual income and lack of health insurance were the main barriers to treatment adherence among patients with diabetes because 64% of the patients without insurance coverage and 6% of the patients with health insurance did not follow up their treatment status. Nam et al. reported that some patients with diabetes split their pills at each meal to reduce their treatment costs [43]. However, introducing and referring patients to charities and NGOs [3] can solve some of their financial problems, but this issue needs more detailed and comprehensive investigation. Lack of insulin is another factor that affects treatment adherence. Habte et al. found that patients unable to prepare their own insulin medication had difficulty adhering to their treatment [28]. Some studies mentioned age and education as factors influencing treatment nonadherence. However, Nelson et al. demonstrated that younger age was an obstacle to treatment adherence [26], while Gholamaliei et al. considered older age as an obstacle to treatment adherence [4]. However, further studies are required to achieve an accurate and logical result.
Cultural and religious beliefs are other factors that may prevent people from adhering to treatment. Mukona et al. demonstrated that sometimes families obliged patients to consult with traditional and religious therapists. Some patients reported seeking help from religious healers because they believed their illness was linked to demons and the curse of generations. On the other hand, consultation with traditional and religious therapists was in some cases cheaper or free, which was attractive to families, especially when the patient had no income. Some participants used herbs to control blood sugar because insulin was expensive and difficult to store. Researchers have found that there may be a correlation between financial problems and cultural and religious beliefs [23]. It should be noted that some cultural and religious beliefs rooted in superstitions and misconceptions may be eliminated by awareness or education, but some other cultural and religious beliefs are too deep to remove. However, there is a need for the relevant authorities to try to change people's misconceptions.
Studies have reported the experience of drug side effects as a barrier to treatment [24]. The side effects of diabetes medications, especially insulin, are unavoidable and may occur in patients who inject insulin [44]. This issue becomes more important when individuals do not adhere to their medication regimen well and changes their doses.
The results of this study can be used to design comprehensive programs to empower patients with type 2 diabetes in treatment adherence by introducing different factors of barriers to treatment adherence among patients with type 2 diabetes.
One of the limitations of this study is that although eligible articles were identified and reviewed, some unpublished studies might have been missed. In addition, as the present study is a scoping review, there was no limitation for selecting articles; therefore, the quality of the articles did not assess. This may affect the study results.
According to the results of this study, it is suggested that educational and counselling services be provided to increase awareness, promote health literacy of patients with diabetes, and motivate and encourage them to follow treatment regimens in order to increase their health and quality of life. Policymakers and planners are also recommended to improve the physical, mental, and social health of patients with type 2 diabetes and their families by designing and implementing educational interventions. Further studies are suggested to examine the effectiveness of educational interventions in promoting treatment adherence and limited health literacy among patients with type 2 diabetes.

Conclusions
The results of the present study provided modifiable and nonmodifiable factors affecting treatment adherence among patients with type 2 diabetes. As most of these factors can be modified, it is possible to take an important step towards empowering patients by implementing targeted educational interventions. Since some of these factors refer to the role of patients' families and health care teams, in addition to empowering and training patients, their families and health care providers also need to be trained to implement treatment adherence among patients with type 2 diabetes.