Hair Cortisol Analysis: A Promising Biomarker of HPA Activation in Older Adults.

Prolonged stress is a potentially harmful and often undetected risk factor for chronic illness in older adults. Cortisol, one indicator of the body's hormonal responses to stress, is regulated by the hypothalamic-pituitary-adrenal (HPA) axis and is commonly measured in saliva, urine, or blood samples. Cortisol possesses a diurnal pattern and thus collection timing is critical. Hair cortisol is a proxy measure to the total retrospective activity of the HPA axis over the preceding months, much like hemoglobin A1c is a proxy measure of glucose control over the past 3 months. The aim of this review is to examine a novel biomarker, hair cortisol, as a practical measure of long-term retrospective cortisol activity associated with chronic stress in older adults. Hair cortisol analysis advances the science of aging by better characterizing chronic stress as a risk factor for chronic illness progression and as a biomarker of the effectiveness of stress reduction interventions.