Background
Diabetes is a chronic disease, and it could cause many serious short-term and long-term consequences [
1] that affect both health and quality of life (QOL) [
2]. The total number of diabetes patients worldwide may rise to about 370 million in 2030 from about 170 million in 2000 [
3]. According to the World Health Organization (WHO), Type 2 diabetes patients accounts for 90% of all diabetes worldwide [
4]. The morbidity of Type 2 diabetes mellitus also have been increasing over past decades [
5].
QOL refers to a person’s individual perception of physical, emotional, and social status [
6,
7]. Type 2 diabetes patients have great pressure to treat themselves, and they have lower QOL than those healthy persons [
8,
9]. For chronic diabetes patients, a complete cure cannot be achieved [
10]. Clinical measures can provide a good estimate of disease control, but the ultimate aim of diabetes care is preventing the patient’s QOL to get worse [
10]. Understanding the predictors and identifying risk factors of QOL is important and these factors may then be targeted for prevention [
6].
There are many different scales that could measure the QOL, such as EuroQol 5D (EQ-5D), Audit of Diabetes Depentent Quality of Life (ADDQoL), Diabetes-Specific Quality of Life (DSQL), Short Form-Series (SF-36, SF-8, SF-12, and so on), and so on. EQ-5D has five dimensions (Modility, Self-Care, Usual Activities, Pain/Discomfort and Anxiety/Depression) and each dimension has three levels [
1]. The ADDQoL scale is composed of two overview items and 18 life domains [
11]. The DSQL scale is a specific instrument for diabetes patients and is used to measure the QOL of Chinese diabetes patients. It includes 27 items and four domains: Physical Function, Psychology/Mind, Social Relation, and Influence of Treatment [
12]. SF-36 consists of 36 questions that stand for 8 fields of life. Four fields stand for the Physical Health (PH): Physical Functioning (PF); Role limitations due to Physical health problems (RP); Bodily Pain (BP); General Health perceptions (GH). Another four fields stand for the Mental Health (MH): Vitality (VT); Social Functioning (SF); Role limitations due to Emotional problems (RE); and Emotional State (ES) [
13].
Recently, many studies [
1,
2,
5,
11‐
24] have reported some related factors of QOL of type 2 diabetes patients. While authors of these studies used different scales which were mentioned above. Take the factor “complication” for an example, Liu et al. [
19] and Xie et al. [
20] used the DSQL scale, while Aldona et al. [
13] and Zu et al. [
20] used the SF series scales to evaluate the QOL of type 2 diabetes patients. Meanwhile, for a same factor measured by a same scale, they even had different opinions about whether it was QOL’s related factor or not. Take the factor “Diet control” for an example, Zu et al. [
20] showed the results that patients who controlled their diet would have a worse QOL than those who did not control diet. While Aldona et al. [
13] showed that the factor “Diet control” was not associated with the QOL of type 2 diabetes patients.
For the reasons mentioned above (preventing the patient’s QOL to get worse is the ultimate aim of diabetes care while the opinions about related factors of QOL were not unitive by the previous researches), and considering the fact that many demographic characteristics could not be modified. The aim of our study was that after searching for studies which reported the related factors (including characteristics related to the disease, life styles and mental health factors) of QOL of type 2 diabetes patients across the internet databases, we pooled their results together via the systematic review and meta-analysis method, to understand the related factors of QOL of type 2 diabetes patients.
Discussion
Type 2 diabetes patients were expected to improve their QOL via self-management and life-time metabolic control [
10]. The QOL was gaining importance as the physiological or clinical outcome parameter [
10]. Therefore, one of the objectives in the management of diabetes was to minimize the deterioration in the QOL [
2]. The aim of our study was to find out the related factors of QOL of type 2 diabetes patients (including characteristics related to the disease, life styles and mental health factors).
After our search, 18 articles were entered into our systematic review and meta-analysis. The 18 studies contained 11 countries and 57,109 research objects, using 5 kinds of scales. Opinions in these studies were not totally same to each other.
After the analysis, we found that complications could affect the QOL of type 2 diabetes patients at almost all aspects. Tang et al. [
33], Shiu et al. [
34], and Wexler et al. [
35] also showed the result that the QOL of T2DM was lower if the patients showed complications. Complications could affect the QOL of type 2 diabetes patients in many ways, such as increasing physical discomfort, decreasing their activity, and reducing their physical state. In addition, these various complications could extend treatment time and add therapy methods [
12]. For instance, the treatment of type 2 diabetes with end-stage nephropathy required not only medical therapy, but also dialysis and even renal transplant [
36]. Meanwhile, complications could increase the cost of type 2 diabetes [
36‐
38]. Therefore, complications may increase the material and mental burden of type 2 diabetes patients. Besides, depression also could cause more complications [
38]. So depression may cause worse QOL of type 2 diabetes patients. It was similar to the result of our study, depression was associated with lower QOL score. The results of studies of Wexler et al. [
35] and Verma et al. [
39] also showed depression was an associated characteristic of QOL of T2DM. Overall, complications and depression could affect the QOL of type 2 diabetes patients together. It was of interest that whether depression should be considered as complication of diabetes rather than comorbidity [
16]. Similarly, for type 2 diabetes patients, knowing adequate information about the natural history of the disease was helpful to develop a positive attitude toward type 2 diabetes [
11]. Fear of hypoglycemia could influence the patients to maintain a high blood glucose level [
40‐
42]. So worry about the disease could be seen as one of the factors that may cause worse QOL.
The relationship between duration of diabetes and the QOL was still controversial [
17]. According to our study, the longer duration could cause the worse QOL. Some studies also reported that increased duration of diabetes was associated with poor QOL in T2DM patients [
43]. It may be caused by that glycaemia control tended to be worse with longer duration due to a decline in beta cell function, and a decline in patients’ attitude and adherence to treatment regimen [
11]. Some previous studies [
44‐
46] reported that glycaemia control was an important determinant of QOL. While checking glucose frequently could be helpful for glycaemia control, so glucose check frequently might be a preventive factor for QOL [
11], similar to our study.
According to our study, physical exercise was preventive to the QOL on most dimensions of SF-36 scale. Physical exercise is beneficial for health in any domain (recreation, transportation and so on) and is recommended by the WHO [
47]. It could help to reduce the risk of diabetes [
48], and is correlated with blood glucose and blood pressure control [
12,
49]. Sung et al. [
50] found that a regular walking was effective for lowering blood glucose and HbA1c in elderly people with type 2 diabetes.
According to our study, diet control had no significant association with the QOL of type 2 diabetes patients. While diet with more red meat was a negative factor of the QOL. A previous study reported that people in the top quintile of red meat intake had a greater chance of having a metabolic syndrome [
51]. The mechanism of the relationship between eating more red meat and QOL was not clearly understood. It was possible a surrogate of some other influenced factors [
12]. For example, the meat-eater could had higher BMI than other people [
12], and women with high intake of red meat tended to have less likely to exercise [
52].
The strongest strength of our study was that it was the first meta-analysis about related factors of the QOL of type 2 diabetes patients. We calculated as many factors as possible, and we classified these factors into 3 groups to make it much clear to understand. Some variables had wide range confidence intervals [such as complications measured by SF-36-Role limitations due to Emotional problems (0.656, 10.387), Depression measured by SF-36-Physical Health (3.184, 10.086) and Mental Health (4.195, 31.383)]. It was because the number of the included researches for each factor was too small. And in meta-analysis, the results with wide confidence interval were always treated as moderate-quality evidences [
53,
54]. So it need more related studies to find out the real association between these factors and QOL of type 2 diabetes patients.
Meanwhile, our study had several limitations. First, due to the language restriction, we included the publications in English and Chinese only. So articles written in other languages were ignored. Second, the included studies have used many different QOL scales and the objective factors of each study was not exactly identical, so many results in our study were pooled by only 2 included articles. Third, in many our included studies, the authors have not showed the negative results. They only reported the factors associated with the QOL significantly. So much information was missing. Fourth, heterogeneity among these included studies may affect the accuracy of our results. Sensitivity analysis and meta-regression could help to find the source of heterogeneity. However, limited to the dispersion and the number of studies, we could not calculate it exactly.