Association of Diurnal Patterns in Salivary Cortisol With Type 2 Diabetes in the Whitehall II Study

Context: The hypothalamic pituitary-adrenal axis is thought to play a role in Type 2 Diabetes (T2D). However, the evidence for an association between diurnal cortisol patterns and T2D is equivocal. Objective: The aimwasto examine the association of cortisol patterns throughout the day with T2D status in a community-dwelling population. Design: This was a cross-sectional study of T2D status and salivary cortisol from phase 7 (2002-2004) of the Whitehall II study, United Kingdom. Setting: The occupational cohort was originally recruited in 1985-1988. Participants: Three-thousand, five-hundred eight white men and women including 238 participants with T2D aged 50-74 years with complete information on cortisol secretion participated. Outcome Measures: We measured diurnal cortisol (nmol/L) patterns from six saliva samples obtained over the course of a normal day: at waking, +30 min, +2.5, +8, +12 hours, and bedtime. The cortisol awakening response and slope in diurnal secretion were calculated. Results: T2D status was associated with a flatter slope in cortisol decline across the day (b = 0.004; confidence interval [CI], 0.001-0.007; P = .014) and greater bedtime cortisol (b = 0.063; CI, 0.010-0.117; P = 0.020) independent of a wide range of covariates measured at the time of cortisol assessment. There was no association between morning cortisol, the cortisol awakening response, and T2D (P > .05). Conclusions: In this nonclinical population, T2D was associated with a flatter slope in cortisol levels across the day and raised bedtime cortisol values.