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Introduction
Depression affects 322 million people (4.4%) worldwide, although the prevalence is highest among middle-aged to older adults (55–74 years), particularly women (World Health Organization, 2017). Between 2009 and 2012, 7.6% of US individuals ƒ12 years were categorized with depression, and women, middle-aged to older adults (40–59 years), and persons living below the poverty line experienced higher prevalence (Pratt & Brody, 2014). Consequently, depression is the leading contributor to disability globally (World Health Organization, 2017), and a significant factor affecting chronic disease management (Chapman, Perry, & Strine, 2005). Non-Hispanic black and Hispanic older adults have higher prevalence of subthreshold and major depression compared to non-Hispanic white older adults (Xiang, Leggett, Himle, & Kales, 2018). Furthermore, racial and ethnic minorities have poor access to mental health care, leading to undiagnosed depression and inadequate treatment (Kim, 2014) that can exacerbate chronic disease and its management.
Depression has been viewed both as an independent determinant (Poole & Steptoe, 2018) as well as a comorbidity of chronic diseases (O'Connor et al., 2015), as persons with chronic medical conditions also have a high prevalence of depressive disorders (Benton, Staab, & Evans, 2007). Individuals with chronic diseases are at an increased risk of depression or depressive symptoms (Chang-Quan, Bi-Rong, Zhen-Chan, Ji-Rong, & Qing-Xiu, 2010a; Chang-Quan et al., 2010b), likely triggered by the financial, emotional, and physical strain of managing chronic disease, although physiological mechanisms have also been proposed (Aziz & Steffens, 2013; Katon, 2011). Alternatively, depression and depressive disorders have been considered as contributors to chronic disease etiology, including cardiovascular disease, diabetes, and obesity (Chapman et al., 2005; Mezuk, Eaton, Albrecht, & Golden, 2008). However, limited evidence exists for pathways in which depression, or depressive symptoms, may facilitate disease development. Studies assessing relationships of depression and disease status have shown associations in both directions for some conditions (i.e. cancer, metabolic syndrome, obesity, cardiovascular disease) (Gothe et al., 2012; Luppino et al., 2010; Nemeroff & Goldschmidt-Clermont, 2012; Pan et al., 2012; Spiegel & Giese-Davis, 2003), while others are less clearly defined (e.g. type 2 diabetes) (Renn, Feliciano, & Segal, 2011; Tabák, Akbaraly, Batty, & Kivimäki, 2014).
One understudied pathway in the depression-chronic disease connection is the role of depression in disturbing the body's allostasis, or process of attaining homeostasis after responding to...