The hypothalamic-pituitary-adrenal (HPA) axis is a key neuroendocrine stress pathway and its principal end product, cortisol, is influenced by genetic, metabolic, and psychological processes (Susman, 1998). Basal cortisol secretion has a typical diurnal cycle with peak levels soon after awakening, and a steep decrease over the remaining day, with this basal dynamic supplemented by episodic cortisol reactivity to unpredictable, uncertain, and novel psychological challenges (Bosch et al, 2009). Such reactivity has widely been considered an endocrine index of the stress response (Miller, Chen, & Cole, 2009). However, in a number of studies, substantial inter- and intraindividual variability to similar challenges has been revealed (Chida & Steptoe, 2009; Kudielka, Hellhammer, & Wüst, 2009; Thorn, Hucklebridge, Evans, & Clow, 2009) and it has been suggested that personality traits may play a significant role in their explanation (LeBlanc, Ducharme, & Thompson, 2004; Oswald et al., 2006; Pruessner et al., 1997).

Two approaches to personality research are well-known: Eysenck’s biosocial approach (Eysenck & Eysenck, 1985a) and the psycholexical approach of the five-factor model (Costa & McCrae, 1985). In both approaches two basic personality dimensions of neuroticism and extraversion are acknowledged. Eysenck proposed a third dimension of psychoticism, reflecting impulsive, antisocial, aggressive, cold, egocentric, unempathic, creative, and tough-minded behaviors (Eysenck, 1992a, 1992b). In the Big Five model, Costa and McCrae (1992), suggest three more fundamental traits: openness, agreeableness, and conscientiousness. Openness involves active imagination, aesthetic sensitivity, attentiveness to inner feelings, preference for variety, and intellectual curiosity (Costa, McCrae, & Dye, 1991). Traits such as trust, straightforwardness, altruism, compliance, modesty, and tender-mindedness are components of agreeableness (Costa et al., 1991). Qualities of order, dutifulness, achievement striving, self- discipline, and deliberation are characteristics of conscientiousness (Costa et al., 1991). Psychoticism is negatively related to agreeableness and conscientiousness (Draycott & Kline, 1995; Eysenck, 1992b; McCrae & Costa, 1985) but may be positively related to some aspects of openness (Eysenck, 1991, 1992b).

The general picture for associations between personality measures and cortisol response to challenge is one of inconsistency. Associations between neuroticism and elevated cortisol responses have been documented in relation to public speaking (Houtman & Bakker, 1991) and mental arithmetic tasks (Habra, Linden, Anderson, & Weinberg, 2003). But neuroticism has also been linked to blunted HPA responses to public speaking and mental arithmetic tasks (Garcia de la Banda, Martinez-Abascal, Pastor et al., 2004; LeBlanc & Ducharme, 2005; Phillips, Carroll, Burns, & Drayson, 2005). A diminished cortisol response to stress (Garcia de la Banda, Martínez-Abascal, Riesco, & Pérez, 2004; Kirschbaum et al., 1995) has also been linked to extraversion, but directionally opposite results have been reported by LeBlanc and Ducharme. Openness has been linked to higher levels on the Trier Social Stress Test (Kirschbaum, Pirke, & Hellhammer, 1993), while participants low in agreeableness (who tend to be mistrusting and hostile) secreted more cortisol during daily life compared to their nonhostile peers (Suarez, Kuhn, Schanberg, Williams, & Zimmerman, 1998). Conscientiousness has been considered a buffer for stress (Korotkov, 2008), and a predictor of good health and longevity (Friedman, 2008). However, associations between conscientiousness and cortisol have not been found (Nater, Hoppmann, & Klumb, 2010; Oswald et al., 2006; Schoofs, Hartmann, & Wolf, 2008). Finally, generally no association has been observed in previous studies between psychoticism and cortisol (Hauner et al., 2008; Kirschbaum, Bartussek, & Strasburger, 1992; Kirschbaum et al., 1995; Schommer, Kudielka, Hellhammer, & Kirschbaum, 1999).

This generally inconsistent picture in regard to personality and cortisol might partly reflect methodological differences. For example, early researchers used the Eysenck Personality Questionnaire-Revised (EPQ-R; Eysenck & Eysenck, 1985b) to assess personality measures (Schommer et al., 1999) while later researchers relied on the NEO Personality Inventory (Costa & McCrae, 1985) or selected other personality questionnaires such as the Freiburg Personality Inventory (Fahrenberg, Hampel, & Selg, 1989) used by Brandtstädter, Baltes-Götz, Kirschbaum, and Hellhammer (1991). In order to increase the validity of our assessment, in this study we assessed relevant personality traits using both the EPQ-R and NEO-FFI (Costa & McCrae, 1992).

Another problem is that in some studies laboratory stressors have been used that lack independent validation of their stress-eliciting properties. In the present study we used a 10-minute-long class presentation to a class as a real life stressor. Speaking in front of an audience is a proven social stressor and has become widely used in stress research (Schoofs et al., 2008). This task involves the potential for negative evaluation by peers (Andrews et al., 2007), which enhances stressor potency for eliciting a cortisol response (Dickerson, Mycek, & Zaldivar, 2008).

Rigorous assessment of cortisol is critical in a study such as this. When cortisol reactivity is assessed, a pretest and posttest measure has typically been used. Many of the authors of those studies used the first saliva sample before the stressful situation as a pretest condition, without taking into consideration that this assessment may be influenced by anticipation. For this reason, we sought to enhance methodological rigor through the use of additional baseline measures taken at the same time of day but on a different day from the stressor manipulation (Klimes-Dougan, Hastings, Granger, Usher, & Zahn-Waxler, 2001). Additionally, many researchers exploring personality and cortisol activity have relied on samples either of adults or of very young children (Bouma, Riese, Ormel, Verhulst, & Oldehinkel, 2009). Late adolescence represents the period before personality and cortisol patterns have been further affected by a long history of major life events or psychopathology, thus permitting relatively “clean” observation of the intercorrelation pattern of cortisol and personality (Hauner et al., 2008).

In summary, in the present study we compared salivary cortisol secreted by a group of students during public speaking to cortisol secreted by the same group of individuals in a nonstressful condition. Differences in cortisol reactivity to the stressor will be correlated with personality traits. Our hypothesis was that the common stressor of public speaking will increase cortisol secretion compared with the control condition. Also, we expected that extraversion, neuroticism, and psychoticism would be related to low cortisol reactivity, and that openness, agreeableness, and conscientiousness would be related to high cortisol reactivity.

Method

Sample

Participants were 75 students at the Universitat de les Illes Balears (UIB) in Spain, of whom 56 were women and 19 were men, with a mean age of 20.9 years. All were volunteers enrolled in a Psychology of Personality class at the UIB across three academic intakes with no exclusion criteria except the provision of both a complete questionnaire and complete cortisol data. No incentives were given for participation.

Instruments

Participants completed the Spanish version of the Eysenck Personality Questionnaire-Revised (EPQ-R; Eysenck, Ortet i Fabregat, & Eysenck, 1997), the 83 items of which yield scores for the key dimensions of extraversion (E), neuroticism (N), and psychoticism (P). Participants also completed the revised short-form version of the Spanish NEO Five-Factor Inventory (NEO-FFI; Costa & McCrae, 1999), the 60 items of which measure the five personality dimensions of neuroticism (N), extraversion (E), openness (O), agreeableness (A), and conscientiousness (C). Both questionnaires have proven reliability and validity and are very widely and routinely used in personality research.

Procedure

At the start of the semester, students completed the EPQ-R and the NEO-FFI scales, and after providing written informed consent, four salivary samples were taken to assess cortisol levels during the late afternoon (between 4 and 6 pm). Two baseline samples were taken on a day during a class period on a day when the student had no paper, examination, or class participation but at approximately the same time of day that stress samples were to be taken. Two stress samples for each participant were taken during a class period in which the student providing the sample had to give a presentation lasting for 10 minutes to the class and answer classmates’ questions after the presentation. The first sample was taken just prior to the presentation and the second 30 minutes after.

Saliva was collected with a cotton swab that the participant had chewed for 1 minute. The sample was then stored in a capped plastic vial (“Salivette” Sarstdet Inc.), centrifuged at 3000g for 3 minutes, and frozen at -80°C until analysis. For the analysis process samples were thawed, mixed, centrifuged, and analyzed without pretreatment. Cortisol was determined by a modification of the Bayer ADVIA Centaur assay, a competitive direct chemiluminiscence immunoassay using rabbit polyclonal antibody. Endogenous cortisol contained in the samples competes with a cortisol labeled with acridinium-ester for the binding sites of the anticortisol rabbit polyclonal antibody-coated paramagnetic particles. The intra- and interassay coefficients of variation were less than 10% for 0.30 µg/dL of cortisol.

Statistical Analysis

A two-way repeated measures analysis of variance (ANOVA) was used to test the effects of stress/baseline and first/second sample on cortisol, and Pearson product moment correlations were carried out to examine associations between cortisol and personality measures.

Results

Descriptive statistics for personality dimensions and cortisol levels assessed in the study are presented in Table 1. Distributions of cortisol data were substantially positively skewed, so values were analyzed as logarithmically transformed with one extreme outlier removed.

A two-way repeated-measures ANOVA was performed with the first and second cortical assessments on the same day and no stress vs. stress as factors (see Figure 1). A significant main effect was obtained for the no stress/stress factor (F(1, 73) = 34.99, p = .000, partial η²= .32. nontransformed M_{no stress} = .50; M_stress = .77) and also for first versus second sample (F(1, 73) = 21.20, p = .000, partial η² = .22. nontransformed M_first = .69; M_second = .58); there was no interaction effect (F(1, 73) = 1.15, p = .29, partial η² = .02).

Next we examined correlations between personality and cortisol measures. All personality measure distributions were plausibly normal except for conscientiousness which was negatively skewed, and psychoticism which was positively skewed. Both, therefore, underwent a square root transformation (with prior reflexion for negative skew). Pearson correlation coefficients were run between cortisol scores and the personality variables. The two cortisol measures taken at the beginning and at the end of both the baseline (CortBL) and stress (CortPS) conditions were averaged and examined to reflect mean cortisol on each day; both had significant positive skewness and were normalized with logarithmic transformation. The difference score, reflecting the cortisol response to the stressor, was calculated by subtracting the baseline average from the stress day average. The distribution of this variable was plausibly normal without transformation. The correlations between personality variables and the three cortisol scores appear in Table 2. Neuroticism scores on the EPQ-R and NEO-FFI questionnaires were positive and highly correlated (.73), as was extraversion (.61). Psychoticism (EPQ-R) and conscientiousness (NEO-FFI) were negative correlated (-.48). Cortisol response to stress was related to conscientiousness (.31) and inversely to psychoticism (-.31). No significant correlations were found between personality and the averaged scores at baseline and on day of stressor, except a small negative relationship between baseline cortisol and the personality trait of conscientiousness (-.23).

Finally, although the sample was primarily female, so that there were not enough males for us to make a powerful analysis, it is possible that being male or female may have some influence on the cortisol response. However multiple regression analyses controlling for gender and also for year of recruitment into the study did not significantly alter the univariate effect sizes reported above.

Discussion

As expected, we found that public speaking was associated with elevated cortisol levels compared to baseline levels taken at equivalent times on a nonstress day, thus validating our use of the public speaking task as an effective stressor. Results were in line with those of Andrews et al. (2007) and Schoofs et al. (2008), with similar stressor conditions. It appears that socially evaluative tasks such as public speaking, which potentially threaten the social self, do elicit robust and reliable cortisol responses (Dickerson et al., 2008). The significant effect for first versus second sample, regardless of day, doubtless reflects the normal background diurnal downward drift of cortisol levels.

Some aspects of personality did correlate with cortisol secretion levels, but overall not to the extent we had anticipated. Conscientiousness was linked to heightened cortisol in the stressed condition. Het and Wolf (2007) showed that female participants with higher cortisol levels coped better with the emotional load of public speaking than did participants with regular or even blunted cortisol secretion, and they conclude that cortisol increases prior to acute stress may be adaptive in reducing negative effects of stress on mood. Conscientiousness is one of the personality dimensions more strongly related to health status perhaps partly because such individuals display good self-control, responsibility, and prosocial attitude towards others (Friedman, 2008). Our results offer a glimpse of one biological mechanism that potentially may explain why conscientious people enjoy better health and live longer: their basal cortisol is lower during nonstressful situations and their greater cortisol reactivity would reflect a better adaptation to stressful situations because this reactivity helps individuals to anticipate, cope, and respond to salient contexts (McEwen, 1998).

By contrast, we found relatively smaller cortisol responses in those higher in psychoticism, a dimension that correlates highly with psychopathy and impairment in stress reactivity (O’Leary, Loney, & Eckel, 2007). In the literature there is a fairly consistent account of antisocial traits, antisocial, impulsive, defiant, and aggressive behavior, relative to low cortisol reactivity in children and adolescents (for a review see Shirtcliff et al., 2009). Our results are consistent with a view that cortisol reactivity blunted under stress may sometimes form part of what is likely to be a wider biological profile associated with antisocial behavior.

Several shortcomings of the present study need to be acknowledged. Psychology students may not be representative even of the general student community, so generalization should be approached cautiously, especially to those with very different demographic or psychobiological characteristics. Replication with a more heterogeneous sample is currently being undertaken by the authors of this article and should help clarify effects of any sampling restrictions. Second, gender interactions should also be addressed in future since an understanding of these interactions can contribute to knowledge of cortisol response to psychosocial exposure (Rydstedt, Cropley, Devereux, & Michalianou, 2009). Finally, our range of questionnaire scores was somewhat restricted and, again, a more heterogeneous sample would be desirable in future work.

In conclusion, in our study the aim was to examine associations between cortisol reactivity to a laboratory stressor and personality. Conscientiousness, a trait associated with resiliency to psychological disorders and better health, was associated with an enhanced cortisol response to stress, while psychoticism, a trait linked to more pronounced psychopathology, was associated with blunted cortisol response. To our knowledge, this is the first study in which the results show that prosocial (and antisocial) personality traits may be predictors of cortisol responses to a stressor.

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This work was supported by research grants from the Ministerio de Educació

n y Ciencia (SEJ2005-05331 and SEJ2007-63837) and by the DGR del Govern de les Illes Balears (8917/2006). The funding agencies had no further role in the study design

in the collection

analysis

and interpretation of data

in the writing of the report

or in the decision to submit the paper for publication. The authors thank Dr. Linda Fidell for helpful methodological consultation and valuable comments and Dr. Clemens Kirschbaum

Phil Evans

and Lucia Dettendorn-Betz for insightful suggestions and careful review of this manuscript.

Appreciation is also due to reviewers including

Moira Mikolajczak

Université

Catholique de Louvain

Louvain

Belgium

Email

[email protected]

Derek Roger

Canterbury University

Christchurch

New Zealand

[email protected]

Gloria Garcia-Banda, Cra. Valldemossa, km 7.5. Edificio Guillem Cifre (B-208), Universitat de les Illes Balears. Email: [email protected]