Homeostatic Regulation of Thirst

Stephen Black sblack at HERA.UBISHOPS.CA
Wed Aug 21 14:47:16 EST 1996

On Wed, 21 Aug 1996, lindsab wrote:

> I began to wonder about the homeostatic regulation of thirst when I 
> saw a post-it note an PhD had tacked up in the lab reminding herself 
> to "Drink water".  
> 				This made me wonder about why the appetite for liquid often seems 
> to lag behind the physiological need for fluids. I have often read 
> that a significant section of the population is chronically 
> dehydrated. 

Sez who? Actually, I think the more usual case is that we ordinarily 
drink considerably in excess of need (e.g. see N. Carlson, Physiology of 
Behavior, 5th ed. 1994, p. 382, where he says "most drinking occurs _in 
anticipation_ of actual need"). Think of the enormous consumption of soft 
drinks, bottled water, tea and coffee and (need I mention it), beer. Our 
kidneys are efficient at saving water, and I would guess that unless one 
is impaired in some way or engaging in extensive exercise in the 
heat, that dehydration is rarely a problem.

 After all, many of us really drink the 8-12 glasses of 
> water per day that nutritionists recommend? 

Do they? And is there any factual basis for such a recommendation?

 I have yet to see anyone 
> write notes reminding themselves to eat or put on a sweater when it 
> gets cold.  Why should the physiological drive to drink be so much 
> easier to ignore?  Humans evolved in a very dry climate indeed and a 
> strong impulse toward adaquete hydration would have been very adaptive 
> indeed.

On the contrary, when true thirst is evoked, it is exceedingly difficult
to ignore. You should read McGee's accounts of people dying of thirst in
the desert (note the "stage of living death", for example) or other
accounts of people in extreme circumstances of water lack reprinted in
A.V. Wolf's old but classic book (titled, I believe "Thirst and Problems
of Water Lack"). There are also accounts of people threatened with 
dehydration due to a lack of anti-diuretic hormone (diabetes insipidus: 
their kidneys can't save water) who show an astonishing drive to seek out 
and drink water. It's a powerful drive, all right.

Stephen Black, Ph.D.                      tel: (819) 822-9600 ext 470
Department of Psychology                  fax: (819) 822-9661
Bishop's University                    e-mail: sblack at hera.ubishops.ca
Lennoxville, Quebec               
J1M 1Z7

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