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 aim was to 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.