The effects of neuroticism on diurnal salivary cortisol and TNF-alpha in Mexican-Americans
Studies have associated chronic stress with psychological and physiological pathology (Wadee et al., 2001). Certain individuals, with high levels of neuroticism, appear to be especially vulnerable to the effects of cumulative stress (Zobel et al., 2004). Neuroticism is associated with dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis (Oswald et al., 2006) and this dysregulation is associated with impaired immune system activity (Maes et al., 1998). The theory of Allostatic Load (McEwen, 1998) provides a framework to examine the relationships between neuroticism, HPA dysregulations, and immune activity in Mexican-Americans.
Forty-nine Mexican-Americans between the ages of 18-38 completed self-report assessments of neuroticism factor/facets and subjective health, provided salivary cortisol for seven time points, and a serum sample for measurement of circulating TNF-alpha.
Results of this study indicate that the factor of neuroticism and the facets of anxiety, depression, and self-consciousness are significant predictors of peak diurnal cortisol. General health also significantly predicted peak diurnal cortisol. However, neuroticism and self reported general health did not predict proinflammatory cytokine levels and although peak diurnal cortisol significantly predicted TNF-alpha level, a positive correlation was found between cortisol and TNF-alpha.
Implications for the findings suggest that healthy Mexican-American individuals with higher levels of neuroticism may experience a dysregulation in HPA axis morning cortisol response and subjective health measured by self-report may be a predictor of morning peak cortisol response. The positive relationship between cortisol and TNF-alpha was significant but interpretation may require further investigation of the immune-neuro-endocrine interactions in Mexican-Americans.