Gender, race/ethnicity, personality, and interleukin-6 in urban primary care patients
Introduction
Gender, race/ethnicity, and individual differences in personality are powerful sources of variation in both psychosocial and biological attributes. Yet the extent to which each is associated with underlying inflammation remains unclear. In this paper, we focus specifically on gender, racial ethnic, and personality variation in the inflammatory cytokine interleukin (IL)-6, because it is an important indicator of allostatic load (De Martinis et al., 2005, Franceschi et al., 2000), included in allostatic load composites (Glei et al., 2007), and hence theoretically linked to stress-related factors which may differ by gender, race/ethnicity, and personality. We note that IL-6 was not originally included in allostatic load composites. It has, however, been show to be highly predictive of mortality (Grunewald et al., 2006, Harris et al., 1999), with mortality risk reportedly doubling at levels of 3.19 picograms per milliliter (pg/ml) (Harris et al., 1999). We also focus on a middle aged and older sample, given the cumulative nature of chronic stress adaptation and systemic inflammation (De Martinis et al., 2005), and on the urban primary care population, given the large minority representation often served by these clinics (Fiscella and Williams, 2004).
Prior reports on gender differences in IL-6 have been mixed. O’Connor et al. (2007) reported higher levels of IL-6 in lipopolysaccharide (LPS)-stimulated monocytes from women compared to men (mean age of 36.2 years). In contrast, others have observed a small but significant increase in LPS-stimulated production of IL-6 in young adult males compared to females (Von Aulock et al., 2006), and another study conducted in young adults found no significant gender differences in levels of serum IL-6 (Yang et al., 2007). Others report higher levels of IL-6 among women in older samples (Grunewald et al., 2006). Suarez (2008) also recently found that sleep may account to some degree for gender differences in inflammation.
Differences in serum IL-6 have also been observed in racially-diverse women over the age of 65, with higher levels of IL-6 observed in African American women compared to Caucasians (Allison et al., 2006, Walston et al., 2005). In contrast, no significant differences in serum IL-6 were observed in African Americans versus Caucasians in a mixed gender sample aged 70–79 (Yaffe et al, 2003). If such differences in inflammation do exist however, they may constitute one conceivable explanation for general susceptibility, or the notion that individuals of disadvantaged socioeconomic status (SES) or disenfranchised groups show increased susceptibility to illness (Berkman and Kawachi, 2000). Furthermore, immune function is strongly influenced by psychosocial factors related to stress and coping (Coe and Laudenslager, 2007), and increased stressors such as perceived discrimination frequently encountered by historically disenfranchised groups (Williams et al, 1997) have been hypothesized to increase allostatic load and resulting inflammation (Carlson and Chamberlain, 2005).
Race/ethnicity and gender represent general demographic group markers. However, considerable individual variation in inflammation may exist within genders and racial/ethnic groups. Five Factor Model (FFM) personality dimensions (McCrae and Costa, 2003), representing the primary axes of individual differences in psychological and behavioral dispositions, index variation in stress, coping, and genetic parameters potentially relevant to immune function and inflammation (Coe and Laudenslager, 2007, Segerstrom, 2000, Segerstrom, 2003). Neuroticism has been linked to exaggerated HPA axis responses to stressors (Eysenck and Eysenck, 1985), and appears associated with higher resting cortisol (Miller et al., 1999), lower antibody response to vaccination for hepatitis B (Marsland et al., 2001) and influenza (Phillips et al., 2005), and lower resistance to a common cold virus after infection (Cohen et al., 2003b). Extraversion is thought to be associated with a lower threshold for sympathetic arousal (Eysenck and Eysenck, 1985, Geen, 1997), and greater natural-killer cell cytotoxity (Miller et al., 1999). Specific Extraversion components of sociability (Cohen et al., 2003a) and positive emotions (Cohen et al., 2003b) are also associated with resistance to common cold, while the latter is also associated with higher antibody titers in response to hepatitis B vaccination (Marsland et al., 2001). One study in an older, partly depressed sample found positive associations between Neuroticism, but not Extraversion and IL-6 (Bouhuys et al., 2004). Other studies have variously reported associations between IL-6 and positive affect (Prather et al., 2007), IL-6 and specific aspects of negative affect such as depression and cynicism that may be a function of poor health behaviors (Sjögren et al., 2006), and no associations between trait negative affect and IL-6 (Marsland et al., 2007).
We examined whether IL-6 varied between gender and/or racial/ethnic groups in a diverse urban primary care patient population. Although prior results have been mixed, we hypothesized that women and minority patients would show higher circulating levels of IL-6, as such differences have appeared at least as often as not in prior studies. We also hypothesized that higher Neuroticism and lower Extraversion would be associated with higher IL-6. In other words, we suspected that while gender and/or race/ethnicity would mark general group differences in inflammation, personality would index individual variability in inflammation within gender and racial/ethmic groups, corresponding to independent effects for each factor. We also explored all 2 and 3 way interactions between these factors.
Section snippets
Participants and procedure
Patients aged 40 and older, recruited in person at the time of clinical visits and through flyers at the Family Medicine Center (FMC) of the University of Rochester Medical Center (URMC), attended a research appointment at the FMC or the URMC General Clinical Research Center (GCRC). At the appointment, participants completed an interview assessing demographics and psychosocial characteristics, the NEO-Five Factor Inventory (NEO-FFI) measure of personality, the Center for Epidemiologic Studies
Unadjusted results
Unadjusted associations between IL-6 and gender, race/ethnicity, and personality traits (Models 1–4, respectively) are shown in the first four columns of Table 2. Higher Extraversion was related to lower, while female gender was related to higher levels of IL-6. A trend suggested that minority race/ethnicity was also associated with higher levels of IL-6.
Adjusted results
Model 5, mutually adjusting gender, race/ethnicity, and personality for one another and for education and age (Table 2) revealed that
Discussion
Our findings indicate that in a racially diverse urban primary care sample, women, minorities, and patients lower in Extraversion—specifically, dispositional activity, but not positive affect or sociability—possessed higher circulating levels of IL-6. Gender and race/ethnicity thus appear to be important dimensions of group differences in IL-6 levels, but after these group differences are accounted for, dispositional activity poses an important source of individual variability in IL-6. We
Acknowledgments
This work was supported by R21AG023956 (JM), 1R24AG031089-01 (JM), T32MH073452 (PD & JL), & K08AG031328 (BC). The study was also supported in part by General Clinical Research Center (GCRC) Grant 5 MO1 RR00044 from the National Center for Research Resources, NIH. We wish to thank the patients and staff of Highland Family Medicine, and the staff of the URMC General Clinical Research Center for their help in conducting this research. We also thank three anonymous reviewers for comments on earlier
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2021, Brain, Behavior, and Immunity - HealthCitation Excerpt :Indeed, it may be the case that some inconsistencies in linking broader personality traits to inflammatory markers may be due to differences in measures that emphasize some facets more than others. Chapman et al. (2009), for instance, established that extraversion was not associated with inflammation at the higher-order level. Yet, they found that activity level (a facet of extraversion) was negatively linked with inflammation.