Biology / Health / Medicine / Science

Falling temperatures

No, the title isn’t a weather prediction, it’s about this study on human body temperatures in the US. It turns out that the truism that the average human body temperature is 37°C is less and less true over time: this study found that even taking into account that body temperatures have always varied around that point on an individual level, overall, the average body temperature is going down. In the UK, the average body temperature (according to the average over 35,000 patients whose temperatures were taken with an oral thermometer) is now 36.6°C.

That’s sort of an interesting fact, of course, but it would be more interesting to know why it’s happening. The authors theorise that it is due to the lower levels of inflammation that a person can expect to have now compared to the historical measurements. If people were always fighting off infections on some level, maybe their body temperatures were higher due to the immune response. They suggest chronic infections of syphilis, tuberculosis, malaria and periodontitis were possibly common enough, along with other infections, to produce an overall rise in the average.

I’m personally not sure that explains the decade-on-decade change they have also observed. Apparently, not only are our body temperatures lower on average, but that’s a trend which is continuing. It’s not clear to me that medicine is changing fast enough now for that to still be the case, and I would expect to have seen a large change at the time antibiotics were introduced. I’m not seeing that trend in their data.

Still, overall changes in inflammation due to changed hygiene habits and lower levels of physical work I could buy — and the observation is interesting in itself.

3 thoughts on “Falling temperatures

    • They discuss some of that and other confounding factors in the study (which is open access — you can read it if you’re interested). The historical samples are pretty big (e.g. one sample set is 83,900). Adjustments were done for BMI and BMI adjusted for height and didn’t change the overall results. Splitting by ethnicity also preserved the effect. Other things like time of the year and time of day are also known for some of the data sets and behaved as expected as well. They also discuss trying to adjust for changes in how temperatures are taken and the accuracy of the equipment; in general, they think the differences would incline towards masking the change (i.e. the change is greater than it appears from the data), not artificially causing or inflating it.

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