The current study investigated if the Big 5 personality traits predicted interleukin-6 (IL-6) levels in a national sample over the course of 5 years. In addition, interactions among the Big 5 were tested to provide a more accurate understanding of how personality traits may influence an inflammatory biomarker. Data included 1054 participants in the Midlife Development in the U.S. (MIDUS) biomarkers subproject. The Big 5 personality traits were assessed in 2005–2006 as part of the main MIDUS survey. Medication use, comorbid conditions, smoking behavior, alcohol use, body mass index, and serum levels of IL-6 were assessed in 2005–2009 as part of the biomarkers subproject. Linear regression analyses examined personality associations with IL-6. A significant Conscientiousness*Neuroticism interaction revealed that those high in both Conscientiousness and Neuroticism had lower circulating IL-6 levels than people with all other configurations of Conscientiousness and Neuroticism. Adjustment for health behaviors diminished the magnitude of this association but did not eliminate it, suggesting that lower comorbid conditions and obesity may partly explain the lower inflammation of those high in both Conscientiousness and Neuroticism. Our findings suggest, consistent with prior speculation, that average to higher levels of Neuroticism can in some cases be associated with health benefits – in this case when it is accompanied by high Conscientiousness. Using personality to identify those at risk may lead to greater personalization in the prevention and remediation of chronic inflammation.
The public health relevance of inflammatory markers is now well-established (Harris et al., 1999), but the psychosocial conditions associated with inflammation are not yet well understood. Early evidence suggested that personality traits are one such factor. Some of the earliest work focused on how relatively specific personality traits (i.e., dispositional depression, anxiety, hostility) had a positive association with interleuken-6 (IL-6) and C-reactive protein (CRP) in both clinically depressed and community based samples (Coccaro, 2006, Graham et al., 2006, Howren et al., 2009, Ladwig et al., 2003 and Marsland et al., 2008).
More recent investigations specifically utilizing the Big 5 taxonomy of broad personality dimensions have extended these earlier findings. For example, in a Sardinian population sample, higher Neuroticism (composed of traits reflecting chronic negative affect such as depression, anxiety, and poor self-esteem) and lower Conscientiousness (composed of traits reflecting self-regulation and goal pursuit) predicted higher levels of both IL-6 and CRP (Sutin et al., 2010). Others have also noted that higher Conscientiousness predicted lower levels of IL-6 over 32 months in older community-dwelling persons (Chapman et al., 2011b), and that higher levels of self-directedness, a trait related to Conscientiousness, were also associated with lower levels of CRP (Henningsson et al., 2008). Other reported Big 5 correlates of higher levels of inflammation include low openness to experience for IL-6 longitudinally (Chapman et al., 2011b), CRP in African Americans cross-sectionally (Jonassaint et al., 2010), and lower levels of extraversion cross-sectionally (Chapman et al., 2009). The Type D personality style, reflecting high Neuroticism and low extraversion, has also been tied to tumor necrosis factor (TNF)-alpha (Dennollet et al., 2008 and Dennollet et al., 2009) in heart disease patients. Importantly, the magnitude of personality–inflammation associations is non-trivial, with a two standard deviation difference in personality linked to odds ratios up to 1.40 (Sutin et al., 2010) for scoring above the high-risk IL-6 cut point of 3.19 pg/ml associated with a doubling of mortality risk (Harris et al., 1999).
There are many reasons why personality may be associated with inflammation, but one pathway which we test in the current study involves health behaviors. According to the health behavior model of personality, levels of certain personality traits (particularly Conscientiousness and Neuroticism) are associated with either engagement in health promoting or health debilitating behaviors (Bogg and Roberts, 2004 and Smith, 2006). In turn, behaviors such as smoking and excessive alcohol use are associated with higher levels of inflammation (Bermudez et al., 2002 and Wannamethee et al., 2005). Many such behaviors also influence adiposity levels, which induces inflammation and engenders chronic diseases with inflammatory components, such as cardiovascular disease (CVD) (Dandona et al., 2004, Guzik et al., 2006 and Yudkin et al., 2000). Prior investigations support the health behavior model, in that adjusting for BMI and other health behaviors does partially attenuate the personality-inflammation link (Chapman et al., 2011b, Howren et al., 2009, Sesso et al., 2007 and Sutin et al., 2010).
