Wrist temperature as a sleep marker in actigraphy

Sleep is closely associated with reductions in core body temperature (CBT), leading to heat loss through the skin. This effect manifests as an increase in distal skin temperature, a hallmark of sleep onset. Actigraphy, a wearable technology for monitoring sleep and circadian rhythms, now includes models with integrated temperature sensors. The present study aimed to determine whether a skin temperature sensor embedded in an actigraph could yield data to more accurately define sleep onset and offset. We collected activity and distal skin temperature data from participants residing in different Brazilian cities with diverse climates, as well as from night-shift workers. The relationship between temperature changes and sleep transitions was analyzed. Wrist temperature consistently rose slightly before and significantly after sleep onset, and decreased slightly before and markedly after sleep offset, regardless of environmental temperature or time of day. These patterns were consistent across latitudes and seasons, robust, and directionally opposite between onset and offset. Overall, the findings support wrist temperature as a physiological marker for contextualizing sleep-wake transitions in actigraphy. Incorporating temperature sensors into actigraphy devices may enhance large-scale, non-invasive sleep monitoring and improve the assessment of sleep in individuals exposed to varied environmental conditions.