Responding to chronic stress: longitudinal perspectives on metabolism

It has recently been suggested that a "stress response" may increase survivorship of individuals, particularly when individuals are undergoing dramatic shifts in resources. A stress response may increase survival by activating two separate physiological pathways that continuously replenish energy stores: activation of the sympathetic-adrenal system (SAS) when mobilization of energy is required for physical responses, and activation of the hypothalamic-pituitary-adrenal (HPA) axis to decrease energy requirements in times of psychosocial stress when energy balance is positive and physical demand decreased. While some studies attribute laboratory-induced, acute mental stressors that activate SAS with increased metabolic cost, no studies have evaluated the influence of chronic, HPA-inducing stressors (when energy balance is positive) on energy expenditure. The present study tests our hy- pothesis that resting metabolic rate (RMR) decreases with prolonged expo- sure to psychological stress. RMR, blood pressure, saliva samples, a 10-item Perceived Stress Scale questionnaire, and a questionnaire of adherence to protocol and weekly academic work were collected on 17 female students for the duration of a 10-week academic term. Saliva samples were assayed for salivary cortisol (indicative of HPA activity). A significant increase in RMR was observed with increased salivary cortisol concentration (p50.028), indicating that HPA activation may lead to an increase in metabolic cost instead of the hypothesized decrease. We suspect that the observed increase in cost could be resulting from increased maintenance requirements caused by physiological responses to chronic stress, including higher blood pressure, heart rate and wear on organ systems.

This study was funded by the Murdock Charitable Trust, reference number 2006194:JVA:11/16/2006.