Quirks & Quarks

You're cooler than your ancestors — by about a degree

Improvements in lifestyle and health care seem to be the cause of a decline in average normal body temperature

A study of a rapidly modernizing group in the Amazon suggests why

Average normal body temperature has declined in the US by about 0.6 degrees C over 150 years, likely due to improved living conditions and better healthcare (Shutterstock / George Rudy)

For reasons that have not been clear, average body temperature has dropped by more than half a degree in people in the United States over about the past 150 years. An explanation for that might come from observations of a similar drop over just two decades in a group of people living in the Bolivian Amazon. 

Michael Gurven, a professor in the Department of Anthropology at the University of California, Santa Barbara looked at long term health data from a group of indigenous people known as Tsimane.

The Tsimane people, like this family, have also experienced a decline in average normal body temperature due to improved healthcare (Michael Gurven)

The data was collected from 2002 to 2018 and looked at health indicators for 5000 people in over 100 villages. The Tsimane are forager-farmers who traditionally live a subsistence lifestyle without access to running water or sanitation. Historically they have experienced a very high exposure to a variety of illnesses in what Gurven described as a pathogen rich environment.

But in more recent years, including the years of the study, more and better healthcare became available to them, including hospital care, modern pharmaceuticals and a government sponsored vaccination program. 

The Tsimane still live in bamboo huts, but have the benefit of a more modern lifestyle and access to better healthcare (Michael Gurven)

Paper in Science Advances

The Tsimane study showed a body temperature decline of roughly 0.05 percent per year over the 16 years - from around 37 in 2002 to around 36.5 in 2018. Gurven suggests that this argues strongly that the longer term body temperature reduction seen in wealthy western populations is likely also a result of improved health and reduced levels of chronic and acute infection and inflammation.

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