There have been studies done to prove that higher levels of cortisol can dull the brain.  See Below.  if a child is well looked after with CAH and the treatment is not overdone, their intelligence levels should not be affected at all in that sense though.  They may have gained an advantage through developement in utero with over exposure to androgens, but I am not sure how that would have affected intelligence levels as such.

 

SHALL WE FLY- OR WALK?! -High cortisol levels dull the brain

High cortisol levels are not only a problem for Addisonians taking too much replacement medication- they are a problem for other mortals too!
Information is accumulating in the biomedical literature from several angles that ’ordinary people’ (non-Addisonians) can have prolonged raised cortisol levels due to psychological stress, or depression, or to jetlag (chronic disruption of circadian rhythms). The excess cortisol causes shrinkage of the part of the brain that is involved in spatial learning and memory.

The diverse studies have been possible because of the precision of modern MRI scanning of the brain (the temporal lobes, or the hippo- campus), easy ways to measure cortisol (saliva being convenient and non interventionist), and appropriate standardised tests of spatial learning and memory impairment.

The study involving air cabin crew was published in the biomedical science journal Nature Neuroscience Volume 4 June 2001 pp567- 568, by Dr Kwangwook Cho from the Umversity of Bristol Medical School (UK). Thanks Jill for sendmg us the article from The Times in the UK, and triggering Jeanette’s exploration of this topic! The Times headline was "This is your stewardess speaking: Er, where are we going?" The research was reported in some NZ newspapers as well.
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To give a bit more detail, it was already known from animal studies that high and sustained cortisol levels cause shrinkage of the hippocampus, a part of the brain involved in memory and spatial leaming. It had already been shown that salivary cortisol levels in cabin crew after repeated exposure to jet lag were significantly higher than after short distance flights. To quote the author, the June 2001 study demonstrates "that significant prolonged cortisol elevations produce reduced temporal lobe volume and deficits in spatial learning and memory. These cognitive deficits became apparent after five years of exposure to high cortisol levels." The study compared air cabin crew in an airline whose policy was less than 5 days between outward flights across at least 7 time zones; with those in an airline whose policy was more than 12 days between such outward flights (and shorter flights between).

I Dr Sheline at the Washington State University School of Medicine reported in 1999 that for medically healthy women with recurrent major depression, shrinkage of the hippocampus was related to the cumulative duration of depression, but not their age.

In the journal Nature Neuroscience in 1998, a US neurophysiologist and assistant professor of psychiatry, Dr Sonia Lupien, reported the relationship between stress, cortisol, and memory impairment, at least in the elderly. About one third of the 51 healthy subjects who took part in the study their average age was 73 suffered from sustained high levels of cortisol over a five-year period. This group displayed poor memory recall when asked to remember images they had been shown 24 hours earlier. These individuals also took longer to find their way through a maze (especially designed to measure spatial memory) and MRI scanning showed their hippocampus was 14% smaller than the groups with low or moderate cortisol.

The good news is that experiments in rats have shown that these brain effects seem to be reversible

The work of Dr Elissa Epel at the University of California (published in the Sept/Oct issue of Psychosomatic Medicine) suggests that being a couch potato prolongs high cortisol levels -and the remedy is exercise!
In a published interview she said: "During severe stress, cortisol increases dramatically. It causes blood sugar to go into the muscles, so you can run from the danger. But these days we don’t need to run, and our stress is psychological. And we tend to be exposed to more cortisol that we’re not using or burning off with physical activity like running from danger. So we sit with it. Too much cortisol makes you vulnerable to infection and major disease, and can also cause the brain’s hippocampus areas to atrophy, impairing memory and the ability to learn. " Same story!

Addisonians are a minority group. There are 99 insulin-dependent diabetics (and more than 300 non-insulin dependent diabetics) in New IZealand for every Addisonian. No wonder it is sometimes hard to get an endocrinology appointment without a long delay! So it is refreshing to see that "mainstream" research is throwing light on issues that also affect us: inappropriate cortisol levels in the blood are linked with woolly thinking and memory problems and the simplest "correction tool" is exercise.

Written by Jeanette Crossley & reprinted with permission from the NZAN July/ August 200 1 newsletter.