A Prospective Study of Diurnal Cortisol and Incident Dementia in Community-Dwelling Older Adults.

Diurnal salivary cortisol was measured in 334 older adults without dementia, at four times on two separate days, under quiet and stressful conditions. In multivariate Cox proportional hazard models, higher global diurnal cortisol secretion was associated with incident dementia (HR = 1.09 [1.02-1.15] per one-unit increase in cortisol measure, p = 0.007) and Alzheimer's disease (HR = 1.12 [1.04-1.21], p = 0.003) over a mean (SD) of 8.1 (4.0) years, independent of potential confounders and stressful conditions. Individuals with incident dementia had a slower rate of cortisol elimination under non-stressful conditions, reflected by higher cortisol levels in the evening, and an abnormal response to stress (blunted evening stress response).