Study of Circadian functions in humans (daily eating, sleep and temperature patterns).

 Study of Circadian functions in humans (daily eating, sleep and temperature patterns).

 

The study of circadian rhythms examines the endogenous (internal) biological clocks that coordinate physiological processes over a 24-hour cycle. In humans, these rhythms are primarily governed by the Suprachiasmatic Nucleus (SCN) in the hypothalamus.

Understanding the interplay between core body temperature (CBT), sleep-wake cycles, and nutritional intake is vital, as chronic disruption (circadian misalignment) is linked to metabolic disorders, cardiovascular disease, and cognitive decline. This study aims to map these three variables over 30 days to observe their phase relationships and stability.

Procedure

The study follows a longitudinal observational design over 30 consecutive days. Participants are required to maintain their "free-living" conditions while adhering to strict data logging protocols.

1. Temperature Monitoring

• Device: Use a continuous wearable thermometer or a tympanic thermometer for manual checks.

• Frequency: Measurements are taken every 2 hours during wakefulness and once immediately upon waking and before sleep.

• Goal: To identify the nadir (lowest point) and peak of the body's thermal rhythm.

2. Sleep Tracking

• Method: A combination of actigraphy (wrist-worn motion sensors) and a daily sleep diary.

• Metrics: Record "Lights Out" time, "Sleep Onset" latency, total sleep duration, and subjective sleep quality on a scale of 1–10.

3. Dietary Mapping

• Method: Real-time logging of all caloric intake using a mobile application.

• Metrics: Record the exact timestamp of the first and last meal (the feeding window).

• Restriction: Participants are asked to note any caffeine or alcohol consumption, as these act as chemical "zeitgebers" that can shift the internal clock.

4. Data Correlation

• Analysis: At the end of 30 days, the data is plotted to see if the temperature nadir consistently occurs ~2 hours before waking and how meal timing influences the onset of evening sleepiness.

Data Sheet:

https://drive.google.com/file/d/1S07rrWUzTnAGmkGZTLdSsnoxMXFST-wj/view?usp=drive_link

Conclusion:

• Average Body Temperature: 37.0 +/- 0.5 degree C
• Sleep/Wake Cycle: Regular 8-hour sleep windows from 11:00 PM to 7:00 AM.
• Metabolic Cues: Three distinct eating events per day at 8:00 AM, 1:00 PM, and 7:00 PM.

·     The 30-day data reveals a highly synchronized circadian system. The core body temperature follows a robust sinusoidal pattern, peaking in the late afternoon and reaching its nadir at approximately 4:00 AM. This thermal dip aligns perfectly with the mid-sleep phase, facilitating deep restorative rest.

·    The feeding window (08:30–19:30) acts as a stable metabolic anchor. By concluding meals three hours before sleep, the subject avoids digestive thermogenesis, allowing the body temperature to drop efficiently for sleep onset. Overall, the minimal phase drift suggests strong entrainment to light and lifestyle cues, indicating optimal physiological health and rhythmic stability.