Positive emotional well-being, health Behaviors, and inflammation measured by C-Reactive protein
Introduction
Researchers have long been interested in how psychological factors affect physical health. While most studies have focused on the relationship between negative psychological states (e.g., depression, anxiety, and anger) and deleterious health outcomes (Das, 2016, Ironson and Fitch, 2016, Pratt et al., 2015), recent literature reflects a growing interest in positive psychological states and their potential impact on health (Seligman, 2008). These states, such as joy, happiness, and contentment, reflect a state of full concentration and pleasurable engagement with the environment and have been associated with favorable health outcomes (Chida and Steptoe, 2008, Pressman and Cohen, 2005).
There are several possible mechanisms by which positive emotional well-being (PEWB) may be associated with health, including better engagement in healthy behaviors (Kassel et al., 2003, Peterson et al., 2013, Steptoe et al., 2005), strengthening of social ties and coping resources (Fredrickson, 2001), and regulation of emotion-responsive biological pathways such as the sympathetic nervous system (Steptoe et al., 2009), the hypothalamic-pituitary-adrenal-cortical axis (Steptoe et al., 2005), immune function (Marsland et al., 2007), and gene expression (Fredrickson et al., 2013). Importantly, each of these pathways has been shown to impact the body's inflammatory processes including proinflammatory cytokine and C-Reactive Protein production (Acabchuk et al., 2017, Albert et al., 2003, Fröhlich et al., 2003, Kiecolt-Glaser et al., 2010, Schneiderman et al., 2005, Visser et al., 1999, Woods et al., 2009). Therefore, in order to better understand the health benefits associated with PEWB, linkages between positive psychological factors and inflammation should be investigated.
C-Reactive Protein (CRP), a highly sensitive marker of systemic inflammation, has received much attention due to its association with coronary heart disease, metabolic syndrome, cancers, and mortality in the general population (Aggarwal and Gehlot, 2009, Casas et al., 2008, Park et al., 2009, Stork et al., 2006). CRP typically shows mild chronic elevations in conditions associated with mild chronic inflammation such as obesity, Type II diabetes, depression, and post-traumatic stress disorder (Segman and Stein, 2015). Release of CRP is mainly determined by Interleukin-6 (IL-6), a proinflammatory cytokine produced by the body's immune system in response to chronic inflammation (Steptoe et al., 2007). While much research has examined the association of CRP with negative affect (Howren et al., 2009, Valkanova et al., 2013), emerging literature suggests that CRP may also be inversely associated with positive affect states.
Positive emotional well-being is defined as the presence of high positive affect and life satisfaction, together with an absence of depression (Snyder et al., 2010). A meta-analysis of 70 prospective observational cohort studies indicated that PEWB is associated with enhanced longevity in healthy and chronic disease populations (Chida and Steptoe, 2008). Recent evidence also suggests that positive affect and life satisfaction may both be inversely related to lower levels of systemic inflammation measured by circulating inflammatory markers such as IL-6 (Stellar et al., 2015), TNF- α (Brouwers et al., 2013), and CRP (Steptoe et al., 2008). For example, Steptoe et al. (2008) showed that higher ecological momentary assessment ratings of positive affect throughout the day were associated with lower plasma levels of both IL-6 and CRP in women but not in men in a large population-based study (i.e., the Whitehall II study). Similarly, Friedman and Ryff (2012) found that positive affect was marginally inversely related to plasma levels of IL-6 and CRP in a national sample of middle-aged men and women. More recently, Brouwers et al. (2013) reported that positive affect measured by the PANAS was inversely related to IL-6 and TNF-α serum levels (but not to CRP) in a sample of patients with chronic heart-failure.
Fewer studies have examined life satisfaction as a correlate of CRP, and those have yielded mixed results. Hamer and Chida (2011) found a significant relationship between life satisfaction and lower CRP when controlling for demographic variables and health behaviors, which reduced to a trend after controlling for negative affect. In contrast, neither Carpenter et al. (2012) nor Friedman and Ryff (2012) found a significant relationship between life satisfaction and CRP after controlling for only demographic factors. These findings reflect uncertainty as to whether life satisfaction relates to CRP, and whether the relationship exists independent of health behaviors and/or depressed mood.
Several lines of evidence indicate that PEWB is related to healthier behaviors, and that health behaviors are in turn related to inflammation. For example, higher PEWB has been associated with better adherence to medication (Gonzalez et al., 2004), greater likelihood of achieving exercise recommendations (Peterson et al., 2013), moderate alcohol consumption (Dear et al., 2002), reduced smoking (Kassel et al., 2003), and lower BMI (Steptoe et al., 2005). In addition, there is evidence that some health behaviors, such as exercise (Woods et al., 2009) and moderate alcohol consumption (Albert et al., 2003), are linked to lower inflammation. Conversely, smoking (Fröhlich et al., 2003) and being overweight (Visser et al., 1999) are associated with higher inflammation. Thus, health behaviors may in part help to explain the association of PEWB with inflammation.
However, there is also evidence suggesting that certain health behaviors may influence PEWB. Exercise programs have been associated with improvements in emotional well-being (Penedo and Dahn, 2005), while obesity has been associated with less frequent positive affect (Carr et al., 2007). Similarly, smoking cessation has been shown to predict improvements in PEWB (Piper et al., 2012), and heavy alcohol use is associated with lower psychological well-being (Dear et al., 2002).
While the handful of studies addressing the PEWB and CRP relationship are suggestive, they have yielded mixed findings. Specifically, the strength of the associations between positive affect and life satisfaction with CRP above depression and health behaviors remains unclear. The first aim of this study was to evaluate, in a large national sample, whether two primary components of PEWB, positive affect and life satisfaction, were associated with lower CRP levels controlling for demographics followed by depression. The second aim was to determine whether these effects would persist after controlling for health behaviors collectively. Third, if we found support for the second aim, we would then examine the extent to which each specific health behavior (i.e., BMI, smoking, alcohol, and exercise) mediated the relationship between positive affect or life satisfaction and CRP. Fourth, this study aimed to examine these relationships in a subgroup of individuals with chronic illnesses.
Section snippets
Method
The present study was conducted as part of the Landmark Spirituality and Health Survey (LSHS) conducted in 2014 among a sample of 3010 adults, representative of the adult U.S population. Data collection for this nationwide, face-to-face survey, was conducted by the National Opinion Research Center (NORC) using clustered random household sampling from 44 national frame areas representing the continental US. The response rate was 50%. The IRB at NORC approved this study. Additional information
Results
Table 1 provides demographic information as well as means and standard deviations for CRP levels, psychological variables, and health behavior variables for both groups. A significantly greater number of individuals in the chronic illness group had clinically elevated CRP (≥3 mg/L) than in the non-chronic illness group (χ2(1) = 34.773, p < 0.001). The chronically ill group was older, less likely to be Asian or Hispanic, and exhibited lower life satisfaction, lower positive affect, and higher
Discussion
This study found that two components of positive emotional well-being, positive affect and life satisfaction, each related to lower CRP levels in a large national sample as well as in a chronic illness subgroup. Furthermore, they do so even after controlling for both demographics and depression, suggesting that this association is not fully attributable to the absence of depression. This finding is especially important because a large literature shows that depression is both a predictor of
Conclusion
Our results add to a growing literature reporting an association between aspects of PEWB, especially life satisfaction, and a health-related biomarker of inflammation. In fact, those with low positive affect or life satisfaction faced increased risk of having clinically elevated CRP. Health behaviors, especially BMI and moderate exercise, accounted for some but not all of this relationship. Future studies should determine whether increasing life satisfaction and positive affect might contribute
Acknowledgements
We thank the John Templeton Foundation (40077) for funding the Landmark Spirituality and Health Survey (Neal Krause, P.I.). The funding source was not involved in the design of the study, preparation of the manuscript, collection, analysis, and interpretation of the data, or decision to submit the article for publication.
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