Dynamics of core body temperature cycles in long-term measurements under real life conditions in women.
Level 4 - case-series / case-control
Uncontrolled observational longitudinal physiological study in a single cohort of healthy participants.
PubMed 29106303 · doi:10.1080/07420528.2017.1375942
What was done
Core body temperature (CBT) was continuously recorded in 37 healthy women (aged 21 to 44 years, median 29 years) using a newly developed intravaginal temperature sensor for up to 102 days under real-life conditions. Sleep logs were collected for 23 participants. Daily CBT curves were assessed using traditional phase markers (peak and nadir) alongside novel quartile-based phase markers (t25, t50, and t75) to quantify the phase, shape, and alignment of temperature rhythms with sleep-wake timing and social schedules.
What was found
Day-to-day variation was prominent for both the timing of the peak and the nadir. The quartile parameters, especially t75, showed closer locking to external time than the nadir. When a nadir occurred close to wake-up time, the subsequent CBT cycle was considerably shorter than 24 hours; when distant from wake-up time, the following cycle was longer, showing an expand/contract pattern. The t-markers also distinguished early from late chronotypes and captured differences between weekend and workday schedules. The abstract reports no exact numerical values, effect sizes, or confidence intervals.
Why it matters
Demonstrating that real-world core body temperature cycles routinely deviate from rigid 24-hour periods challenges standard assumptions derived from controlled laboratory settings. Segmenting curves via novel quartile markers may provide more stable anchors for tracking ambulatory human circadian rhythms.
Limits
The sample is modest (37 women, with sleep logs for only 23) and limited to adult females using an intravaginal sensor. No specific numerical data or variance metrics are provided in the abstract, and confounding variables such as menstrual cycle phase, physical activity, and ambient light were not quantified in the summary.
Cited by
- context In order to wake up feeling refreshed and energized, core body temperature must increase by approximately 1 to 3 degrees Fahrenheit.