A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich.
Level 4 - case-series / case-control
Descriptive baseline observational study in a single prospective cohort
What was done
Researchers conducted a descriptive analysis of baseline oral temperature measurements in 148 healthy adult men and women aged 18 to 40 years admitted to an inpatient clinical research unit for vaccine trials. Oral temperatures were recorded one to four times daily over 3 consecutive days using an electronic digital thermometer to evaluate historical standards established by Carl Wunderlich.
What was found
The mean baseline oral temperature was 36.8°C (98.2°F), lower than Wunderlich's classic 37.0°C (98.6°F). The upper limit of the normal oral temperature range was 37.7°C (99.9°F) overall and 37.2°C (98.9°F) in the early morning, compared to the historical threshold of 38.0°C (100.4°F). Temperature exhibited diurnal variation with a nadir at 6:00 AM, a zenith between 4:00 PM and 6:00 PM, and a mean amplitude of 0.5°C (0.9°F). Women had slightly higher baseline temperatures than men, and black participants showed a trend toward higher temperatures than white participants.
Why it matters
This study demonstrates that the canonical normal body temperature of 98.6°F (37.0°C) is an overestimation and provides modern, time-dependent thresholds for defining fever and normothermia.
Limits
The study evaluated a modest sample of 148 participants restricted to healthy individuals aged 18 to 40 years in an inpatient unit, precluding generalization to older adults, young children, or outpatient ambulatory settings. Data were limited to oral thermometry over a short duration of 3 days.
Cited by
- context Human core body temperature is maintained around 98.7 degrees Fahrenheit, which is the optimal temperature for human enzymes to function.