A PERSON-CENTERED APPROACH TO MODELING DIURNAL CORTISOL: THE IMPORTANCE OF DIFFERENCES IN AGE AND STRESSOR EXPOSURE

Open Access
Author:
Dmitrieva, Natalia O.
Graduate Program:
Human Development and Family Studies
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 10, 2011
Committee Members:
  • David M. Almeida, Committee Chair
  • Laura Klein, Committee Member
  • Eric Loken, Committee Member
  • Douglas Teti, Committee Member
Keywords:
  • aging
  • stress
  • cortisol
  • hypothalamic-pituitary-adrenal axis
Abstract:
Cortisol is a marker of HPA-axis activation that may be one of the biological mechanisms linking chronic stressors and heterogeneity in age-related health declines (e.g., Epel, 2009; Miller, Chen, & Cole, 2009). The aims of current dissertation were three-fold: 1) to identify person-centered profiles of diurnal cortisol among a national sample of U.S. adults, 2) to examine age-associated differences in diurnal cortisol profiles, and 3) to explore whether and how three different forms of stressful experiences differentially predict the relation between age and diurnal cortisol profiles. Growth Mixture Models with latent time basis were used to estimate daily profiles of diurnal cortisol among participants taking part in up to four consecutive days of saliva collection (N=1,622; age ranged between 34 and 87 years old). The 3-class solution provided the best model fit across all four days of saliva collection, with results further indicating a striking stability within estimated parameters of each profile across the entire study period. The majority of respondents exhibited a “typical” profile, characterized by relatively low awakening and bedtime levels, coupled with robust slopes following awakening and prior to bedtime. Approximately one-quarter of participants experienced an “elevated” profile, distinguished by a high morning level and blunted cortisol awakening response and diurnal slope. One-tenth of respondents exhibited a waking level that was similar to that of participants in the typical class, but remained remarkably “flat” throughout the rest of the day, showing weak cortisol awakening response and diurnal slope. In contrast to elevated and flat profiles, the typical profile was positively associated with younger age, higher self-rated health, and a greater likelihood of being employed, and negatively associated with minority status, cigarette smoking, and being male (p’s<.05). After accounting for relevant control variables, the typical profile was associated with younger age (p<.001). Additional analyses demonstrated that report of greater chronic stress in early midlife is associated with a lower probability of exhibiting a typical profile, and an increased risk of exhibiting a flat profile (p<.001). The current dissertation demonstrates the utility of the Growth Mixture Modeling approach to the study of diurnal cortisol, and supports previous work showing that older age, minority status, and poorer physical health and health behaviors are associated with a deviation from the robust waveform of diurnal cortisol. Furthermore, results show that chronic stress in early midlife may increase the likelihood of a flatter rhythm of diurnal cortisol–a profile that is typically associated with older adulthood.