Distress and type 2 diabetes-treatment adherence: A mediating role for perceived control.

The rising prevalence of type 2 diabetes represents a significant challenge for population health in the US and internationally. Although it is well established that reductions in hemoglobin A1c (A1C), a key index of glycemic control in diabetes, can substantially reduce the risk of diabetes complications (United Kingdom Prospective Diabetes Study, 1998; Nathan et al., 2005), about half of US adults with diabetes are not at goal for A1C (Stark Casagrande et al., 2013) and many report nonadherence to prescribed medications (DiMatteo, 2004; Rubin, 2005). Nonadherence is associated with poor control of A1C, blood pressure and lipids, and increased risk of hospitalization and mortality (e.g., Ho et al., 2006); it is also linked to less effective care – providers are less likely to intensify treatment when indicated for nonadherent patients (Grant et al., 2007). Thus, identification of factors associated with diabetes treatment nonadherence is important and could guide interventions to improve health outcomes. Among patient-level factors, depressive symptoms have been consistently related to treatment nonadherence across a variety of chronic illnesses (DiMatteo, Lepper, Croghan, 2000). A meta-analysis of 47 independent samples showed that higher levels of depressive symptom severity are consistently associated with problematic diabetes self-management across various behavioral domains, including medication adherence (Gonzalez et al., 2008a). Beyond their consistent association with poorer diabetes self-management, depressive symptoms are also related to important diabetes health outcomes over time, such as development of complications (Lin et al., 2010; Black, Markides & Ray, 2003) and mortality (Park, Katon & Wolf, 2013). However, it is important to note that these relationships do not appear to be limited to cases of clinical depression, such as major depressive disorder (MDD). Indeed, depressive symptoms that fall well below MDD diagnostic thresholds are associated with worse self-management both cross-sectionally (Gonzalez et al., 2007) and longitudinally (Gonzalez et al. 2008b); they also predict complications and mortality (Black et al., 2003). Evidence suggests that these ‘subclinical’ depressive symptoms may often represent emotional distress specific to the burdens of living with diabetes rather than a co-morbid depressive mood disorder (Fisher et al., 2007). The need to differentiate diabetes-related emotional distress from depression has led to the development of widely used measures of ‘diabetes distress’ (Polonsky et al., 1995; Polonsky et al., 2005) and of behavioral interventions to directly target diabetes distress (Fisher et al., 2013). Greater precision in distinguishing between depression and diabetes distress could guide the selection of appropriate interventions for patients (Gonzalez, Fisher & Polonsky, 2011). Both diabetes distress and depressive symptoms have been independently associated with medication nonadherence, cross-sectionally and longitudinally, in adults treated for type 2 diabetes (Fisher et al., 2010; Gonzalez et al., 2007; Gonzalez et al., 2008b; Gonzalez, Delahanty, Safren, Meigs & Grant, 2008c; Aikens, 2012). However, the conceptual and measurement overlap between these constructs contributes to inconsistencies in the literature (Gonzalez, Fisher & Polonsky, 2011; Fisher, Gonzalez, & Polonsky, 2014). For example, although early studies showed consistent associations between depressive symptoms and glycemic control (Lustman et al., 2000), more recent studies examining change over time have failed to demonstrate this relationship (e.g., Georgiades et al., 2007; Fisher et al., 2010; Aikens, Perkins, Lipton & Piette, 2009; Aikens, 2012) and suggest that diabetes distress is more closely associated with glycemic control (Aikens, 2012; Fisher et al., 2010). Thus, although emotional distress is clearly implicated in sub-optimal diabetes treatment adherence and outcomes, there is inconsistency in these relationships. Some of this inconsistency may result from an over-reliance on self-report measures of depressive symptoms, which are often more reflective of general distress than clinical depression (Coyne, 1994) and may be particularly vulnerable to overlap with diabetes distress (Gonzalez et al., 2011). Despite the size of the literature on the relationship between emotional distress and diabetes self-management, little research is available to shed light on how distress is linked to diabetes self-management. Social-cognitive variables may play an important role. Negative mood states are known to have a direct influence on self-efficacy, generally reducing perceived ability to carry out activities across various domains (e.g., Kavanagh & Bower, 1985; Salovey & Birnbaum, 1989). Thus, one mechanism linking emotional distress with poor diabetes treatment adherence and health outcomes may involve self-efficacy. Several studies have reported evidence to support self-efficacy as a mediator of the relationship between depressive symptoms and type 2 diabetes self-management (Chao, Nau, Aikens, Taylor, 2005;Wagner, Tennen, Osborn, 2010). Evidence has also been reported for self-efficacy for diabetes management as a mediator of the relationship between depressive symptoms and glycemic control among males with type 2 diabetes (Cherrington, Wallston, Rothman, 2010). Although there is a rich literature that links perceptions of self-efficacy for specific activities to the amount of effort and persistence expended on these activities (Bandura, 1982), these perceptions should be distinguished from one’s perceived ability to meaningfully affect an outcome of interest, or perceived control (Bandura & Wood, 1989; Skinner, 1996). Bandura viewed self-efficacy and perceived control as linked through reciprocal causation (Bandura & Wood, 1989) and described perceived control as a precondition to the optimal execution of efficacious behaviors – “if people approach situations as largely uncontrollable, they are likely to exercise their efficacy weakly and abortively,” whereas, “when people believe the environment is controllable…they are motivated to exercise fully their personal efficacy” (Bandura & Wood, 1989, p.806). Individuals with type 2 diabetes and elevated depressive symptoms report less perceived control over diabetes (Egede & Ellis, 2008; Macrodimitris & Endler, 2001) and greater perceived control is consistently associated with lower A1C (Egede & Ellis, 2008; Macrodimitris & Endler, 2001; Sharry, Moss-Morris, Kendrick, 2011). This relationship may be mediated through improved adherence, as perceived control has also been consistently associated with better diabetes self-management (e.g., Hampson Glasgow, & Toobert, 1990; Skinner & Hampson, 2001). Thus, although evidence supports self-efficacy and perceived control as potential mediators of the distress – diabetes self-management relationship, prior studies have not examined their independent effects. We sought to advance our understanding of the relationships among emotional distress, diabetes treatment adherence, and glycemic control in adults with treated type 2 diabetes by examining direct and indirect pathways linking these variables. We used measures of depressive symptoms and diabetes distress as indicators of emotional distress and evaluated perceived control and self-efficacy as sequential mediators of the relationships between emotional distress, medication adherence and glycemic control.