The awakening cortisol response and blood glucose levels

The hypothalamic-pituitary-adrenal axis is characterized by a marked circad ian cycle with heightened activity in the morning. This is synchronized to awakening such that free cortisol increases two to three fold in the first thirty to forty five minutes following awakening - the awakening cortisol r esponse. It has been suggested that this activity, by mobilizing energy res erves prepares the body for the metabolic demands of the day. Similar argum ents are applied to the cortisol response to psychological challenge. Parad oxically the cortisol response to a psychosocial stressor is abrogated in f asted individuals with low blood glucose. Also cortisol response to a psych osocial stressor is positively correlated to blood glucose levels after glu cose load. We examined if the same relationship applies to the awakening co rtisol response. There was no correlation between the cortisol response and awakening blood glucose levels. Moreover a group with mean blood glucose a t the bottom of the euglycemic range, identified by split at the median for glucose level upon awakening, showed no deficit in cortisol response. Henc e the physiology of the awakening response differs to that of a psychologic al stress response. These data challenge the view that an oxidisable substr ate for energy metabolism is permissive for cortisol responses. In addition the present findings do not support a predominantly gluconeogenic role for morning cortisol activation.