HEALTH

Our bodies are getting cooler. The ‘new normal’ is more than one degree less than the standard 98.6 degrees F (37 C), which has been considered our healthy temperature for more than 200 years.

But doctors are finding that the new healthy body temperature is 97.5 degrees F (36.3 C) and this could have a big impact on understanding the severity of an illness or fever.

This cooling was first noticed in a study of 35,000 adults in the UK in 2017, when the average body temperature was measured at 97.9 (36.6 C) degrees F, and a separate study in 2019 saw that lower again, to 97.5.

This cooling has been sudden. The decline in body temperature in the last 20 years has been as great as anything seen in the previous 200 years, say researchers at the University of California at Santa Barbara.

But why? The researchers think that improved hygiene, cleaner water and better sanitation have led to fewer infections—which could explain the decline in the West, but a similar drop has been seen among indigenous people in Bolivia, who are living in the same conditions as their forebears.

Perhaps it’s the availability of drugs or air conditioning, other theories suggest, but, again, the Tsimane people of Bolivia don’t have access to those, either. “Body temperatures have declined even in this tropical environment, where infections still account for much of the morbidity and mortality,” said researcher Michael Gurven.

But perhaps it’s actually down to our fixation on a normal temperature. There’s a range and even one person’s temperature can fluctuate during the day and can vary by as much as a degree from the early morning to late afternoon. It also changes as we age, and as women go through the menstrual cycle. And, as everyone knows, it rises after strenuous activity.

So perhaps we didn’t check enough after Carl Wunderlich, a German physician, set the healthy temperature reading two hundred years ago. There was no standard normal then, and there isn’t one today.

(Source: Sciences Advances, 2020; 6: eabc6599; doi: 10.1126/sciadv.abc6599)