Circadian rhythms monitoring and core body temperature
The scientific study of bioperiodic phenomena dates back to the 18th century. A biological rhythm can be described as the stable and regular oscillation of a variable between high and low values over time. It is often schematically represented as a sinusoidal variation of the variable of interest over a given period.
The most studied and well-documented rhythms, due to their impact on daily life, are circadian rhythms, which have a cycle close to 24 hours. They are characterized by minimum and maximum values that define the amplitude of the rhythm over the period.
These biological rhythms originate primarily from the Suprachiasmatic Nucleus (SCN) of the Hypothalamus, which acts as a “conductor” for multiple independent oscillators, each regulating one or more biological functions.
Circadian rhythms are thus regulated by an internal biological clock that determines the fluctuations of physiological functions over a 24-hour period. The rhythms observed result from a combination of internal mechanisms and external influences.
External factors influencing circadian rhythms mainly include the alternation of day and night, as well as the cycle of activity and rest imposed by societal schedules.
The relative plasticity of bioperiodic phenomena allows individuals to anticipate rhythmic changes in their environment.
Biological processes therefore exhibit temporal variations dictated by internal factors and influenced by external time cues, also known as Zeitgebers. However, differences in acrophase (timing of peak values) or amplitude can be observed among individuals exposed to the same environmental conditions. This variability is referred to as chronotype, which identifies a person’s circadian profile, distinguishing between “morning types” and “evening types” based on their habitual sleep-wake preferences.
The age of the individual is often a determinant of circadian amplitude and the robustness of rhythms.
Finally, the level of physical activity can also influence rhythms.
Disruptions in temperature rhythms can indicate issues such as sleep deprivation, jet lag, or shift work-related disturbances.
Circadian rhythms monitoring and core body temperature
Core temperature follows a structured and reproducible rhythm, making it a reliable marker for assessing a person’s circadian profile due to its strong interactions with various physiological and cognitive functions.
- Typically, core body temperature reaches its lowest value in the early morning (known as the bathyphase of the rhythm).
- It peaks in the late afternoon or evening (acrophase).Regular circadian rhythms monitoring through core body temperature measurement provides valuable information about an individual’s biological clock and its alignment with external time cues.
Disruptions in temperature rhythms can indicate issues such as sleep deprivation, jet lag, or shift work- related disturbances.
Impact of Circadian Misalignment
Under stable living conditions, all biological rhythms of an individual are synchronized with the environment. However, certain life circumstances can temporarily or chronically disrupt circadian rhythms.
- Jet Lag: Traveling across time zones (eastward or westward) causes a transition period where circadian synchronization is disrupted. During this adjustment phase, lasting several days, biological rhythms become misaligned with environmental cues, leading to sleep disturbances, appetite regulation issues, and overall discomfort.
- Shift Work: One of the most significant sources of chronic circadian disruption. The frequent inversion of sleep and wake cycles leads to continuous misalignment of circadian processes.
In this context, circadian rhythm monitoring, particularly through continuous core body temperature tracking, serves as a reliable indicator of an individual’s biological rhythm, revealing potential desynchronization.
When core temperature fails to align with environmental cues, it can lead to:
- Sleep disorders,
- Metabolic disturbances,
- Mood disorders.
For example, people with irregular work schedules often experience disruptions in their circadian rhythm, leading to sleep deprivation and an increased risk of chronic diseases such as obesity, diabetes and cardiovascular conditions.
Interventions can then be adapted to remedy these disturbances.
By monitoring core body temperature patterns, interventions can be tailored to help restore circadian alignment and mitigate the negative effects of circadian rhythm disruptions.