Sleep disturbances are correlated with decreased morning awakening salivary cortisol

Morning and evening salivary cortisol levels were correlated with sleep parameters in 14 patients with primary insomnia and 15 healthy controls. Salivary cortisol was sampled immediately after awakening (T1), 15 min later (T2), and immediately before going to bed (T3) for 1 week at home. In parallel with this, subjects estimated parameters of sleep in a daily sleep log. Patients and controls were all non-smokers who did not differ regarding morning awakening time or bedtime. Cortisol after awakening was significantly decreased in primary insomnia. Salivary cortisol at the time of awakening correlated negatively with the subjective estimation of sleep quality, i.e. a low salivary cortisol level directly after awakening correlated with a higher frequency of nightly awakenings (r=-0.50), a diminished sleep quality (r=-0.34) and a decreased feeling of recovery after awakening (r=-0.35; all p<0.05). Furthermore, awakening cortisol was negatively correlated with the Pittsburgh Sleep Quality Index (r=-0.43) and with a questionnaire on sleep-related cognitions with the subscales rumination in bed (r=-0.56) and focusing on sleep-related thoughts (r=-0.46; all p<0.05).