Individual differences in the phase and amplitude of the human circadian temperature rhythm: with an emphasis on morningness-eveningness.
Level 3 - non-randomized controlled study
Observational cross-sectional study comparing physiological circadian parameters across chronotype groups and sexes
PubMed 10849238 · doi:10.1046/j.1365-2869.2000.00196.x
What was done
Ambulatory core body temperature was continuously recorded over 6 days in 172 young adults (101 men, 71 women). Temperature minimum (Tmin) and amplitude were calculated using complex cosine curve fitting. Subjects completed the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ), the Circadian Type Inventory (CTI), and the MMPI-2 (scored for PSY-5 personality variables) to evaluate relationships between circadian phase/amplitude, chronotype, personality, and sex.
What was found
Average Tmin occurred at 03.50 h in morning-types, 05.02 h in neither-types, and 06.01 h in evening-types. Tmin occurred about a half-hour later in men than in women. Overall Tmin occurred approximately in the middle of the 8-h sleep period, but occurred closer to wake time in subjects with later Tmin and increasing eveningness. Delayed temperature phase was associated with larger amplitude, which was driven by lower nocturnal temperatures.
Why it matters
This study provides physiological validation of subjective chronotype questionnaires, demonstrating that morning- and evening-types differ markedly in the timing of core body temperature minima and its phase-relationship to sleep.
Limits
The sample was limited to young adults. Data were collected via ambulatory recording rather than under constant routine conditions, meaning masking effects from activity, posture, and meals were not eliminated in a laboratory setting. Specific numerical results for personality variables (MMPI-2) and variance measures were omitted from the abstract.
Cited by
- context In order to wake up feeling refreshed and energized, human body temperature must increase by approximately 1 to 3 degrees Fahrenheit.
- partial In order to wake up feeling refreshed and energized, human body temperature must increase by approximately 1 to 3 degrees.