Cortisol is a stress-related hormone with a robust circadian rhythm where levels typically peak in the morning hours and decline across the day. Although acute cortisol increases resulting from stressors are adaptive, chronic elevated cortisol levels are associated with poor functioning. Studies have shown age-related changes in cortisol levels. The present study investigated the relationship between salivary diurnal cortisol and functional outcomes among older adults undergoing inpatient post-acute rehabilitation.Thirty-two older adults (mean age 78 years; 84% men) in a Veterans Administration inpatient post-acute rehabilitation unit were studied. Functional outcomes were assessed with the motor component of the Functional Independence Measure (mFIM; where mFIM change = discharge - admission score). Saliva samples were collected on 1 day at wake time, 45 minutes later, 11:30 AM, 2 PM, 4:30 PM, and bedtime. We analyzed the relationship between cortisol measures and functional outcomes, demographics, and health measures.The analyses consistently showed that greater functional improvement (mFIM change) from admission to discharge was associated with lower comorbidity scores and higher cortisol levels at 2 PM, 4:30 PM, and bedtime. A morning cortisol rise was also associated with greater mFIM change.Measurement of cortisol in saliva may be a useful biological marker for identification of patients who are "at risk" of lower benefits from inpatient rehabilitation services and who may require additional assistance or intervention during their post-acute care stay.
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