Effects of nocturnal decline in core body temperature and heart rate on sleep: a comparative study of two age groups

Background: Nocturnal core body temperature (CBT) decline is reflected in decreasing heart rate (HR) and is linked to sleep stage distribution, a relationship which is influenced by age and subject to temperature manipulation. Objective: The present study investigates the relationship between CBT, HR, and sleep stage distribution by comparing two studies with healthy males: young and middle-aged men. The aim is to examine how these physiological systems might be interrelated. Materials and methods: Data from two independent studies were compared to examine nocturnal sleep stages, CBT, and HR time courses. Results: The findings revealed that younger men exhibited improved sleep consolidation, characterized by longer total sleep time and more slow-wave (SWS) and REM sleep, along with a sustained nocturnal decline in CBT and HR. In contrast, middle-aged men exhibited poorer sleep continuity and a less-pronounced decline in CBT, followed by an earlier rise. The CBT changes were reflected in HR. Conclusion: These results suggest that the nocturnal profile of CBT may be linked to variations in HR and fluctuations in sleep stage distribution. Interventions that facilitate nocturnal heat loss and a reduction in CBT and HR could potentially support sleep quality across age groups, particularly regarding SWS.