Poor night's sleep predicts following day's salivary alpha-amylase under high but not low stress

Although sleep is linked to physiological stress systems like the autonomic nervous system (ANS), research is still limited regarding night-and-day interactions between nocturnal sleep characteristics, stress, and diurnal parameters of salivary alpha-amylase (sAA) as a surrogate marker of ANS activity. Fifty healthy university students rated their chronic stress burden and completed two five-day periods of ecological momentary assessment - under everyday conditions of both low stress (beginning of semester) and high stress (final examination preparation). Participants collected saliva six times daily and reported on the previous night's sleep (quality, latency, duration, disturbances) immediately after awakening. Additionally, a sub-sample wore actigraphs recording 'time in bed'. In contrast to previous assumptions, poor sleep predicted lower sAA awakening values, more decreased awakening responses, and steeper diurnal slopes the following day only under high stress, but not under low stress. Diurnal sAA parameters did not predict the following night's sleep characteristics. The sAA profile does not seem to be sensitive to everyday occurring sleep variations, but rather seems to be an indicator of more prolonged stress induced ANS dysregulation.