In the US, the normal, oral temperature of adults is, on average, lower than the canonical 37°C established in the 19th
century. We postulated that body temperature has decreased over time.
Using measurements from three cohorts--the Union Army Veterans of the
Civil War (N = 23,710; measurement years 1860–1940), the National Health
and Nutrition Examination Survey I (N = 15,301; 1971–1975), and the
Stanford Translational Research Integrated Database Environment (N =
150,280; 2007–2017)--we determined that mean body temperature in men and
women, after adjusting for age, height, weight and, in some models date
and time of day, has decreased monotonically by 0.03°C per birth
decade. A similar decline within the Union Army cohort as between
cohorts, makes measurement error an unlikely explanation. This
substantive and continuing shift in body temperature—a marker for
metabolic rate—provides a framework for understanding changes in human
health and longevity over 157 years.
