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Exploration of basal diurnal salivary cortisol profiles in middle-aged adults: Associations with sleep quality and metabolic parametersThe use of saliva samples is a practical and feasible method to explore basal diurnal cortisol profiles in free-living research. This study explores a number of psychological and physiological characteristics in relation to the observed pattern of salivary cortisol activity over a 12-h period with particular emphasis on sleep. Basal diurnal cortisol profiles were examined in a sample of 147 volunteers (mean age 46.2177.18 years). Profiles were constructed for each volunteer and explored in terms of the area under the curve (AUC) of the cortisol-awakening response with samples obtained immediately upon waking (0, 15, 30 and 45 min post waking) and at 3, 6, 9 and 12 h post waking to assess diurnal decline. Diurnal mean of cortisol was based on the mean of cortisol at time points 3, 6, 9 and 12 h post waking. Psychological measures of perceived stress and sleep were collected with concurrent biological assessment of fasting plasma glucose, insulin, blood lipids and inflammatory markers. Blunted cortisol profiles, characterised by a reduced AUC, were observed in the majority (78%) of a middle-aged sample and were associated with significantly poorer sleep quality and significantly greater waist-hip ratio (WHR). Blunted cortisol profiles were further associated with a tendency to exhibit a less favourable metabolic profile. These findings suggest that reduced cortisol secretion post waking may serve as an additional marker of psychological and biological vulnerability to adverse health outcomes in middle-aged adults.