Rapidly declining body temperature in a tropical human population.

Area of Science:

• Physiology
• Anthropology
• Epidemiology

Background:

• The standard human body temperature (BT) has historically been accepted as 37.0°C.
• Recent observations suggest a decline in BT over the past two centuries, particularly in the United States, concurrent with decreased infection rates and increased life expectancy.
• The widespread nature and underlying causes of this BT decline remain under-researched.

Purpose of the Study:

• To investigate the phenomenon of declining human body temperature in a population experiencing socioeconomic and epidemiological changes.
• To determine if the observed decline in body temperature is a generalizable trend and to explore potential contributing factors.

Main Methods:

• Longitudinal study of 5,481 Bolivian adults (age 15+) from a pathogen-rich environment, involving 17,958 body temperature observations over 16 years.
• Analysis of body temperature trends in relation to infections and lifestyle factors.
• Exploration of potential causes including physical activity, body composition, antibiotic use, and thermal environment.

Main Results:

• Bolivian forager-farmers initially exhibited a mean body temperature around 37.0°C in the early 21st century.
• Body temperature declined significantly over the study period, at a rate of approximately 0.05°C per year, reaching ~36.5°C by 2018.
• While infections and lifestyle factors explained some variation in body temperature, they did not account for the observed temporal decline.

Conclusions:

• Human body temperature has shown a significant decline in the studied Bolivian population over a 16-year period.
• The decline in body temperature is not fully explained by changes in infection rates or common lifestyle factors.
• Further research is needed to identify the precise causes of this temporal decline, with potential factors including shifts in physical activity, body composition, antibiotic consumption, and the thermal environment.