Salivary chromogranin a reflects autonomic regulation during “wake to sleep” and “sleep to wake” transitions

Abstract Background This study investigated the association between salivary chromogranin A (CgA) and parasympathetic nervous activity (PSNA) during transitions in and out of sleep (Sleep–Wake transitions). Autonomic regulation across the transitions is critical in daily functioning and stress recovery. Although salivary CgA is recognized as a biomarker of acute stress, its relationship with autonomic changes during Sleep–Wake transitions remains unclear. Therefore, we examined whether salivary CgA levels reflect changes in PSNA across the transitional periods. Methods Eighty-eight healthy university students aged 20–25 years participated in this study. Saliva samples were collected before bedtime and after final waking. Heart rate variability was assessed using a portable monitor, and high-frequency normalized units (HFnu) were used as an index for PSNA. Changes in HFnu were calculated over 60 min before and 60 min after sleep onset and final waking. Results No significant sex differences were found in HFnu or CgA levels after waking, although the men had significantly higher CgA levels before bedtime than the women. Those with a smaller reduction in HFnu from sleep to waking had significantly lower CgA levels after waking ( p = 0.024, d = 0.24) and a smaller ΔCgA (after waking CgA–before bedtime CgA, p = 0.018, d = 0.25) than those with a larger decrease in HFnu. Conclusions Salivary CgA levels after waking and ΔCgA reflect PSNA change during Sleep–Wake transitions. Our results suggest that salivary CgA and HFnu levels provide complementary insights into Sleep–Wake transitions and can be used as indicators of sleep quality.