Pain, depression, and fatigue: loneliness as a longitudinal risk factor.

Pain, Depression, and Fatigue: Loneliness as a Longitudinal Risk Factor Close and caring relationships clearly influence physical health and longevity (Burman & Margolin, 1992; Holt-Lunstad, Smith, & Layton, 2010). For example, loneliness, the experience of perceived social isolation, enhances risk for a wide range of health problems; people who were lonelier reported worse physical health, experienced more chronic diseases, and were more likely to develop coronary heart disease than those who felt more socially connected (Sugisawa, Liang, & Liu, 1994; Thurston & Kubzansky, 2009). Indeed, the odds of survival are 45% lower among lonely compared with non-lonely people, an effect that is on par with the negative health effects of obesity and inactivity (Holt-Lunstad et al., 2010). Importantly, the link between loneliness and mortality remains after accounting for health-relevant risk factors (Luo, Hawkley, Waite, & Cacioppo, 2012; Perissinotto, Stijacic Cenzer, & Covinsky, 2012). Much less is known about the links between loneliness and somatic symptoms like pain, depression, and fatigue. Mounting evidence suggests that pain, depression, and fatigue function as a symptom cluster within a variety of populations, including multiple sclerosis patients, fibromyalgia patients, cancer survivors, and community dwelling adults (Bower et al., 2000; Forbes, While, Mathes, & Griffiths, 2006; Jaremka, Fagundes, Glaser, et al., in press; Nicassio, Moxham, Schuman, & Gevirtz, 2002; Ohayon & Schatzberg, 2003; Thornton, Andersen, & Blakely, 2010; Walker, Katon, & Jemelka, 1993). For example, cancer survivors were 2 - 4 times more likely to simultaneously experience pain, depression, and fatigue than what would be expected by chance alone (Laird et al., 2011). The pain, depression, and fatigue symptom cluster was also more common among cancer survivors and community dwelling adults than the combination of any two of these symptoms on their own (Reyes-Gibby, Aday, Anderson, Mendoza, & Cleeland, 2006). Researchers have also used cluster analyses to demonstrate the co-occurrence of pain, depression, and fatigue (Motl & McAuley, 2009, 2010). The pain, depression, and fatigue symptom cluster also affects peoples’ quality of life and may share an underlying biological mechanism. Pain, depression, and fatigue often accompany serious illness and place people at risk for poor health and mortality (Becker et al., 1997; Hardy & Studenski, 2008; Schulz et al., 2000). Furthermore, pain, depression, and fatigue are a collective source of distress within a variety of populations, perhaps because they cluster together and mutually reinforce each other (Lenz, Pugh, Milligan, Gift, & Suppe, 1997). For example, lung cancer survivors and multiple sclerosis patients with higher symptom cluster levels had poorer quality of life than those with lower symptom cluster levels (Fox & Lyon, 2006; Motl & McAuley, 2010). The administration of proinflammatory cytokines induces “sickness behaviors,” behavioral changes that resemble depression and fatigue, like anhedonia and lethargy (Dantzer, O’Connor, Freund, Johnson, & Kelley, 2008), and the experience of pain is partially mediated by elevated inflammation (Marchand, Perretti, & McMahon, 2005). Because pain, depression, and fatigue cluster together, are a collective form of distress, and share a common biological mechanism, it is useful to investigate them as a cluster. The identification of a common risk factor can promote interventions that simultaneously alleviate all three symptoms. Interpersonal relationships clearly affect health, and thus loneliness may be one common risk factor for the development of the symptom cluster. Initial research supports this possibility. For example, lonelier people reported more concurrent physical pain than those who felt more socially connected (Jaremka, Fagundes, Glaser, et al., in press). Compared to their less lonely counterparts, lonelier people also experienced more concurrent depression and fatigue and became more depressed from one year to the next and more fatigued from one day to the next (Cacioppo, Hawkley, & Thisted, 2010; Cacioppo, Hughes, Waite, Hawkley, & Thisted, 2006; Hawkley, Preacher, & Cacioppo, 2010; Jaremka, Fagundes, Glaser, et al., in press). Taken together, this research suggests that lonely people may develop pain, depression, and fatigue over time. Longitudinal studies that simultaneously examine all three symptoms are needed to help identify risk factors for the development of the symptom cluster over time. The current research consisted of two longitudinal samples: 1) cancer survivors and benign (non-cancer) controls and 2) older adults caring for a spouse with Alzheimer’s disease or a related dementia (caregivers) and non-caregiver controls. We chose these two samples because cancer survivors and people caring for a loved one with a serious medical condition are more distressed than community dwelling adults (Kiecolt-Glaser et al., 2003; Reyes-Gibby et al., 2006). In addition, older adults are highly vulnerable to the health problems resulting from pain, depression, and fatigue, including mortality (Hardy & Studenski, 2008; Moreh, Jacobs, & Stessman, 2010; Schulz et al., 2000). Thus, it is particularly important to understand the factors that promote pain, depression, and fatigue among these and other distressed and vulnerable groups. We hypothesized that loneliness would be related to concurrent symptom cluster levels and increases in the pain, depression, and fatigue symptom cluster over time. Although prior evidence suggests that cancer survivors and caregivers are more distressed than community dwelling adults (Kiecolt-Glaser et al., 2003; Reyes-Gibby et al., 2006), we expected the relationship between loneliness and the symptom cluster to be the same across these populations. We also explored sleep quality and aerobic exercise as two potential mechanisms linking loneliness and the symptom cluster, based on prior research connecting both to loneliness and/or somatic symptoms (Brown et al., 2012; Cacioppo et al., 2002; Landmark, Romundstad, Borchgrevink, Kaasa, & Dale, 2011; McMillan & Newhouse, 2011; Stepanski et al., 2009). Identification of common mediating pathways provided a second way to identify potential interventions that could simultaneously alleviate all three symptoms.