nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
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Friday, December 31, 2010

Why Is 98.6 F Normal?

Humans, like most mammals, hover around this temperature.  Given that we keep a constant temperature, why this one?

I ran across this study online (mBio, the journal of the American Society for Microbiology, Nov 9).  It's not an experimental work, but a mathematical model for what temperature would best serve mammals ( of which we are one) in terms of protection from infection, balanced by the cost of maintaining that temperature.
"Assuming that a relationship exists between endothermy and reduced susceptibility to certain classes of microbes, we hypothesized a tradeoff relationship whereby the high costs of endothermy were mitigated by protection against infectious diseases."
As with all models, the results depend on the assumptions.  As an aside, this explains why so many people argue about global warming; the predictions are based on models.

In this case, the researchers set up the model to say that, as body temperature increases, microbial diseases will find it harder to infect the host...the higher temperature making it inhospitable for the germs to grow and spread.  Countering that, the organism must work harder and harder to maintain a higher temperature, driven by caloric intake.  At some point the mammal can't eat enough to fuel the higher temperature.

So, they hypothesize there must be an optimum temperature where you get the best "fitness" to survive.  Putting it all together, their model spit out the following curve:

And found that the maximum fitness (on the y-scale) occurs at about 37 degrees C...or 98.6 F.

Nice correlation, but there are probably about a hundred other variables that play a part.

Which brings me to body temperature as a clinical indicator.  Over the years, I have seen many patients with normal body temperatures that are above or below 98.6.  It's normal...for them; and it's usually not more than a degree either way.  The figure of 98.6 was arrived at by averaging a bunch of "normal" people.  This means there will be "normals"  above and below.

Some patients get it, others don't.  Those that don't sometimes medicate a temperature that doesn't need medicating.  And doctors facilitate this by suggesting anti-pyretics (fever reducing drugs) "just in case."

As a patient, myself, I don't take anything for a low-grade fever.  (Not that I believe in "natural" healing; if it's strep, I'm taking antibiotics.)  I discuss fever with my patients, the pro's and con's of treating it, and when...and let them decide.

Doc D

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