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

Abstract 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.