Background: In 1851, the German physician, Carl Wunderlich, obtained the axillary temperatures of 25,000 patients, thereby establishing the current standard for human body temperature of 98.6¡F. Recent studies of temperature in modern populations, however, have consistently reported a lower temperature range. Using data from three cohorts, we investigated whether mean body temperature has changed over time.
Methods: We compared body temperature measurements of white men from three cohorts: the Union Army Veterans of the Civil War, 1860-1940 (UAVCW, number of measurements N=54,809), the National Health and Nutrition Examination Survey I, 1971-1975 (NHANES, N= 7,541) and the Stanford Translational Research Integrated Database Environment, 2007-2017 (STRIDE, N=271,784).
Results: Consistent with WunderlichÕs findings, the observed temperature in 30 year-old white men from the UAVCW cohort was 98.66¡F (95% CI: 98.62 - 98.69 ). Within the UAVCW itself, we observed a significant birth cohort effect, with temperatures of earlier cohorts consistently higher than those of later cohorts (p<0.001). Mean temperature from NHANES, adjusted for age, was 98.37 ¡F (95% CI: 98.34 - 98.41). The corresponding value from STRIDE was 98.03 ¡F (95% CI: 98.03 - 98.04). Because the last cohort used digital rather than mercury thermometers, based on published estimates, we adjusted the UAVCW and NHANES measurements down 0.2¡F when making cross-cohorts comparisons. Temperature readings from NHANES and STRIDE were consistently lower than those from UACWV (by 0.2 ¡F and 0.4 ¡F respectively) across all ages (Figure 1).
Conclusion: Human body temperature shows a birth cohort effect with mean normal body temperature decreasing since the 19th century by 0.4¡F. Because we observed the birth cohort effect within a cohort where measurements were consistently obtained, we believe this drop reflects physiologic change rather than measurement bias. Although we are still establishing the the modern ÒnormalÓ temperature by age and gender, our observed mean temperature (oral digital) for 30 year-old white men is 98.03 ¡F (95% CI: 98.03 - 98.04).
Figure 1. Body temperature for age in three cohorts
J. Parsonnet, None