A recent prospective study by Schmitz et al. (1) concluded a dose-response relationship between recurrent (subthreshold) depressive symptoms and impaired functioning and impaired health-related quality of life (HRQoL) in participants (n = 1,064) with type 2 diabetes during five annual follow-up assessments. The results of this study confirm that (subthreshold) depressive symptoms are common and highly recurrent in type 2 diabetes (2). This is of general concern, as depression in type 2 diabetes is strongly associated with not only suboptimal quality of life but also a 1.5-fold increased mortality risk (3). However, we have some concerns about the assessment of HRQoL, one of the primary outcome measures of this study. The World Health Organization (WHO) defines quality of life as an individual’s “perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns” (4). The WHO discriminates six major domains within quality of life, namely physical health, psychological well-being, level of independence, social relationships, environment, and spirituality. HRQoL refers to the perception of one’s health and the impact of health problems on quality-of-life domains (5).
We question whether Schmitz et al. assessed HRQoL in their study as they used two items of the Centers for Disease Control and Prevention HRQoL instrument that measure the number of unhealthy days due to physical health and the number of days that mental health has been not good in the previous 30 days. By using these two questions, the authors assessed self-reported mental and physical health, but not the perceived impact of health problems on the different domains. Moreover, in the study by Schmitz et al. HRQoL was reflected in one dichotomized score (impaired vs. not impaired). However, our concern is that this transformation of a continuous score (based on the two questions) into a dichotomized score has resulted in a considerable further loss of information. Besides concerns about the HRQoL measures, we also noticed that Schmitz et al. particularly focused on subthreshold depression; findings regarding the effects of severe depression on functioning and HRQoL were neglected. For example, having experienced four subthreshold depressive episodes and one or more severe depressive episodes appeared to be associated with poor functioning and impaired HRQoL (with comparable relative risk ratios). This finding should be mentioned in the title and the conclusion of the article, which only focuses on the role of subthreshold depressive symptoms.
Finally, Schmitz et al. (1) concluded: “Early identification, monitoring, and treatment of recurrent subthreshold depressive symptoms might improve functioning and quality of life in people with type 2 diabetes.” We hold the opinion that based on this data set this conclusion is rather far-reaching as authors did not evaluate effects of identification, monitoring, and treatment of recurrent subthreshold depressive symptoms on functioning and HRQoL.
Article Information
Duality of Interest. No potential conflicts of interest relevant to this article were reported.
