In this study, 31.3% of the participants with type 2 diabetes had a Type D personality. This rate was consistent with the ranges reported previously among Dutch (22.8–55.8%) [11, 39] and Chinese (27.9–41.4%) [10, 40] adults with type 2 diabetes.
In this study, the mean HbA1c level of people with Type D personality was the same as that of people without Type D personality. Nefs et al. [11] similarly reported no difference after subdividing people without Type D personality into three groups based on scores higher or lower than the cutoff of 10 for the NA and SI sum scores (NA+SI−, NA−SI+, and NA−SI−). In contrast, another study that analyzed the continuous scores of the NA and SI sums found a significant relationship between Type D personality (NA) and HbA1c [9]. Li et al. [41] suggested that the association between Type D personality and HbA1c might differ with the analysis method, including whether Type D was operationalized as a categorical or continuous variable.
Type D personality has mostly been included as a categorical variable (e.g., Type D vs. not Type D) using a cutoff point of 10, while the personality was included as a continuous variable using scores from 0 to 28 for both the NA and SI constructs. Regarding the categorical approach, the cutoff point of 10 was criticized based on the value of the median split [42]. However, the cutoff point of 10 was demonstrated as accurate in classifying Type D vs. not Type D using item response theory analysis among people with cardiovascular diseases [43]. Those against the categorical approach insisted that Type D personality was more accurately represented by the continuous constructs of NA and SI [42] or was analyzed more effectively using a continuous interaction method including quadratic NA and SI effects [44]. This controversy means that further exploration is needed into how to deal with the Type D personality variable.
In this study, those with Type D personality had poor HRQOL. This finding was consistent with that of the sole study conducted on people with type 2 diabetes [9]. That previous study measured HRQOL using a generic instrument (the World Health Organization QOL-BREF: WHOQOL-BREF) that measured physical health, psychological variables (e.g., self-esteem), social relationships (e.g., social support), and environment (e.g., physical safety) [45]. The generic type is applicable when measuring HRQOL across healthy and disease populations [7]. In clinical situations, using a disease-specific type of HRQOL instrument designed to focus on specific problems induced by an illness and its treatment, such as diabetes, is more effective [37]. We recommend conducting more studies on the relationship between Type D personality and HRQOL, with a particular focus on using a diabetes-specific HRQOL instrument.
The present study was the first that we know of to test the association between Type D personality and diabetes outcomes (HbA1c and HRQOL) through multiple mediators among people with type 2 diabetes. In this study, the two hypotheses for the indirect effects through both diabetes distress and social isolation were supported. This mediation-based research provided new information on how people with Type D personality easily experience negative emotions in response to the burden of living with and managing diabetes, and might have fewer interpersonal contacts with others (e.g., with family, friends, or health professionals) and be more socially withdrawn, which will negatively impact blood glycemic control and HRQOL. This new information may contribute to furthering comprehensive theory development regarding Type D personality and its effects on people with type 2 diabetes.
Implications for practice
In this study, the findings for the indirect effects suggest directions for furthering practice for people with type 2 diabetes. First, we recommend that health professionals monitor clients with type 2 diabetes to determine the presence of Type D personality, which is a risk factor for adverse blood glycemic control and HRQOL. The health professionals must then plan and provide interventions toward reducing diabetes distress and social isolation, particularly for those with Type D personality. For example, we suggest that applying diabetes-specific psychological interventions had supporting evidence from a meta-analysis of randomized controlled trial studies toward reducing diabetes distress [46]. Others have indicated that using active listening and talking about the emotional experiences of patient also exert similar effects on reducing diabetes distress when compared with a psychological intervention [47]. Chen and Schulz [48] asserted that social interventions based around information and communications technology (ICT) such as using the internet or web-based apps would promote social contact and alleviate social isolation by providing connections with the outside world, improving social support, increasing engagement with activities of interest, and boosting self-confidence. ICT interventions using digital devices may be particularly useful during the current coronavirus disease-19 pandemic, which requires non-face-to-face contact, social distancing, and restricted gatherings [49].
Strengths and limitation
The first strength of this study was the use of a bootstrapping method for the statistical mediation analysis. The traditional method for a mediation test by Baron and Kenney [50] has previously being the most common. However, this method has been criticized for its lack of statistical power and its failure in testing indirect effects, and no longer seems to be recommended [31, 51]. The normal theory approach, called the Sobel test, has been used as a type of mediation analysis, but is criticized due to its inability to cope with indirect effects that have an asymmetric distribution [51]. To overcome the normality assumption, it is recommended to use the bootstrapping method, which provides more power in detecting indirect effects and reduces the risk of type I errors [52]. Structural equation modeling (SEM) is also frequently used for mediation analysis, and has the advantage of accounting for random measurement errors; however, results from a sufficient sample are substantially identical when applying the SEM and PROCESS-bootstrapping methods [53]. The second strength of the present study was the consideration of potential covariates among general participant characteristics, which might have threatened with the findings of the mediation model.
The main limitation of this study was its cross-sectional design, which induced difficult temporal interpretations of the mediation effects between Type D personality and adverse diabetes outcomes. Further research is recommended to use a longitudinal design.