# Temperature and Longevity

The other day I was talking to a friend whose PhD work (many years ago) involved experiments to determine whether it was safe to expose humans to ultrasound, for example in sonography. The hypothesis was that heating effects are the primary way that ultrasound causes tissue damage. One of the experiments involved determining the length of time required to create lesions in soft tissue when it is heated to various temperatures. As expected, a nice curve emerged. One of the students in the lab had the bright idea of extrapolating this curve to see how long it took for tissue damage to occur at body temperature; the result was not far from the average human lifespan. The implication is that at 98.6 degrees, we are slowly cooking ourselves to death.

## 9 Replies to “Temperature and Longevity”

1. Johannes says:

Just out of curiosity: Are such measurements in scientific circles really done in imperial units? (Coming from one of the few countries where SI is standard I’m often a little confused when people talk habitually in degrees Fahrenheit, despite coming from an academic world)

(Of course, 98.6 °C would be close to the boiling point of water and therefore fitting for the metaphor of cooking oneself to death.)

(And 98.6 degrees would be an obtuse angle, of course ;-).)

2. Ax says:

I was going to say “correlation, not causation”, then I realized there isn’t even correlation. Pure coincidence on this one.

How do you define “the average human lifespan”?

Some rough figures (using wikipedia numbers attributed to UN studies) give global average human lifespan at 67.2 years, with upper end (for Japan) at 82.6 and lower (for Swaziland) at 39.6. And those’re only contemporary values, not considering historical changes in life expectancy.
I doubt that normal human body temperature has undergone corresponding changes.

3. Hi Johannes– As far as I know, nearly all science and engineering in the US is done in SI. However, informal communication (my blog is informal, of course) usually uses Imperial units.

4. Michael Norrish says:

So, I can assure I will live longer by half-starving myself to death (attested elsewhere), and being cold. Pah! Live large and burn out young!

5. Vaibhav Garg says:

If water at 100 °C cooks a potato in 15 minutes, would water at 20 °C cook it in 75 minutes? Ever?

6. Hi Vaibhav- I don’t know much about this but I do remember from chemistry class that all possible reactions are happening all the time, but at hugely varying rates. So yes, the chemical reactions that cook a potato are still happening at 20 degrees. Of course, in practice other reactions (like rotting) will affect the potato much faster.

7. Better to burn out than fade away, Michael!

8. Anonymous Cowherd says:

@7: Based on *my* high school chemistry knowledge, the key concept here is “equilibrium”. Basically, yes, the “cooking” reaction is happening at 20 degrees, but the reverse reaction, the “uncooking” reaction, is happening at the same rate, so the potato will never become fully cooked. By raising the temperature, we speed up the “cooking” reaction and slow down the “uncooking” reaction, so that the potato’s equilibrium state is much closer to “fully cooked”.