The Global Decline of Human Body Temperature: Evidence for a Metabolic and Immunological Crisis

Average human body temperature has declined significantly since the mid-20th century in the populations where it has been longitudinally measured, shifting from the historical norm of 98.6°F to between 97.7°F and 97.9°F. This review explores potential mechanistic connections between this downward trend to parallel increases in chronic illness, immune dysregulation, metabolic disease, and susceptibility to persistent infections. A significant body of research suggests that body temperature both reflects and modulates immune function and basal metabolic rate, and it is documented that declines in temperature are associated with suppressed innate immunity, impaired cellular defense, and metabolic dysfunction. Multiple environmental factors, including heavy metal toxin exposures, antibiotic-induced microbiome disruption, and chronic opportunistic infections may be contributing to thermoregulatory impairment. Integrating these findings, this review proposes that declining human body temperatures may represent an underrecognized biomarker of population-level metabolic collapse and immunosuppression. Understanding the drivers of this trend is essential to addressing the rising burden of chronic illness.

Keywords: Human body temperature, 98.6°F, thermoregulation, metabolic rate, chronic disease, innate immunity, heavy metals, antibiotics, microbiome, immune suppression, chronic inflammation