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Wednesday, September 26, 2012

Cortisol, Stress and Sayinguncle

Incredible but true, this is today's comment on a Kevin Drum post.

I have a problem with the argument that cortisol levels show that low social status is correlated with high stress,  with the argument not the conclusion.  How did levels of cortisol become the best measure of stress ?  In the first place, there has to be some independent measurement of stress which lead to the conclusion that stress causes high cortisol levels.  So we know cortisol levels are correlated with stress.  

But then cortisol levels are treated as an objective measure of stress.   How did that happen ?  Correlated with is not the same as the same as.   An indicator does not become the one right indicator just due to the passage of time.

I happen to know of one very early experiment related to how it was decided (correctly I'm sure) that cortisol levels have a lot to do with something rather like stress.  Some people were being trained to be paratroopers.  Levels of various molecules (including nerve growth factor (NGF) a signal upstream from cortisol) were measured resting, after their first jump and after they were told they would jump for the first time the following day but before the jump.  

Clearly being told that you are going to jump out of a plane whether you want to or not is stressful.  But note what else is going on -- the people were being ordered around.  A decision was made over which they had no control.

It happens to be a fact that every article on how low status people suffer more stress which I hav ever encountered mentions cortisol levels.  I ask does cortisol measure stress or the experience of having to bite one's tongue because one is in the present of a more powerful mammal (submission saying_uncle or something) ?  Or both ? How would we know ?  

I note that the source of high quantities of NGF (which triggers release of cortisol) was the salivary glands of adult male mice.  Not female not juvenile (not there).  Exactly the mice who struggle for dominance and exactly in the fluid which enters a rival mouse following a bite.  OK so if I were to bite (I don't really I don't bite) I would want to inflict pain, stress, fear and makemsayuncleness.

Letting a concrete objective indicator take the place of the abstract subjective phenomenon we wish we could measure is tempting but it doesn't constitute proof of anything.


Anonymous said...

politely, I think you are showing that you didn't bother to do your homework on the rather large body of info on cortisol and stress;

your problem is that you are not reading the right stuff; I think it is pretty well established in humans, which we know from people with addison's that cortisol is secreted in response to stress;

or go to a good academic or medical library and consult a text on endocrinology

Anonymous said...

here are some links to full text articles from pubmed that talk about the role of cortisol and stress
J Endocrinol. 2002 Oct;175(1):99-112.
Plasma binding proteins as mediators of corticosteroid action in vertebrates.
Breuner CW, Orchinik M.

Integrative Biology, Patterson Laboratories, Room 141, University of Texas at Austin, Austin, Texas 78712, USA.

Stressors elicit a complex but variable suite of endocrine events. Comparative studies of the stress response have focused primarily on the adrenocortical response to stress, in particular the measurement of plasma levels of glucocorticoids. However, a number of other factors contribute to and modify cellular and organismal responses to glucocorticoids. Notably, plasma corticosteroid binding globulins (CBGs) can regulate the general availability of steroid to tissues, and/or direct the delivery of hormones to specific sites. In this paper, we discuss possible functions of CBG and mechanisms of CBG action, review CBG characteristics among vertebrates, and discuss our recent studies indicating that CBG may indeed modulate responses to stressors. For example, in house sparrows, we found that basal and stress-induced concentrations of total corticosteroid (cortisol or corticosterone) (CORT) vary seasonally, but CBG concentrations change proportionally, so that free CORT concentrations appear static year-round. In contrast, in white-crowned sparrows and tree lizards, CBG concentrations change under conditions when total CORT levels do not, resulting in significant changes in circulating free CORT. These differences in free CORT are masked if CBG is not accounted for. We have also found that the binding properties of CBG vary considerably between species and need to be determined empirically. Such studies led to the observation that CBG in several species may also serve as a functional androgen binding protein; this is especially important for birds, because previous studies had concluded that birds lack androgen binding globulins. We propose that consideration of CBG is paramount to understanding the role of glucocorticoids in mediating behavioral and physiological responses to stress.

Robert said...

I certainly didn't do my homework. But I still think I have a non-trivial thought.

First for cortisol to be a good indicator of stress it has to be released in response to stress and not in response to anything else. This is a claim which is very hard to demonstrate (impossible to flat out prove) because one can't prove a negative.

But the other thought is that the word "stress" as used in the Cortisol literature (which again I haven't read) does not necessarily have the exact same meaning as the word "stress" used on ordinary converstaion.

Not totally another thought. But what if cortisol is released in particular in response to being pushed around or dominated. It isn't easy to design an experiment in which people are subjected to stress but don't feel put upon by the experimenter.

Imagine that stress as usually defined is high when one is in control and has great responsibility. How could the effect on Cortisol levels be measured ? It is hard to study people who are in control -- they not the scientist must decide what happens.

So I don't see how my concerns could be based on ignorance. I don't see how they could be addressed in an experimental setting.

The only information we have is that noted by Drum plus the Whitehall study -- suggesting either that great power is not stressful *or* that it causes a kind of stress which doesn't cause high Cortisol.

This is almost a linguistic (or maybe metaphysical) argument. We can't have a useful operational definition of "stress" which corresponds exactly the the ordinary English meaning (which is too vague to be useful for science). So we can't possibly know how scientific results relate to our vague semi defined concepts.