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Stress and Depression: how are they linked?Abundant research shows that stress and depression susceptibility ARE linked. As mentioned in the last paragraph on the 'pregnancy hormones' page, CORTISOL is the body's natural stress-coping hormone, in non-pregnant as well as pregnant individuals. This is the final hormone to be produced in the body's cascade of 'stress hormones'. If your body feels stressed, from pain, infection or emotionally threatening stimuli, your brain will help you to cope with this perceived stress by sending chemical messages to the rest of the body. It does this in the following way: The first hormone that the brain produces in response to stress is called CRH. CRH in turn causes the production of a second hormone just outside the brain, called ACTH. ACTH travels in your blood stream to the adrenal glands (above the kidneys) where it causes them to release CORTISOL. Cortisol acts in various ways on tissues in the body to help you deal with stress (the effects are commonly known as the 'fight or flight' response). Cortisol, being a clever hormone, quickly switches off its own production by feeding back to the brain and shutting off the production of CRH and ACTH. This keeps stress in check so that you don't become to overwhelmed by it, but also keeps the hormones in check so that you can keep on responding to new stresses many times a day without exhausting the body's store of stress hormones.
So what IS the link between stress and depression? Well, the theory goes something like this. A perception of stress, be it mental or physical, that goes on for a long time (i.e. it is sustained or chronic), means that the stress hormone axis is activated too much and too consistently and stops keeping itself in check. This is not so difficult to understand. If we overuse our joints we might get arthritis; if we overindulge on sugar and refined carbs we over-tax our pancreas and might get diabetes. Same sort of thing.
Many research studies have looked at the stress hormone cascade in depressed individuals and have found that it is over-reactive. Levels of the stress hormone cortisol have been found to be higher in a significant number of people suffering from depression. Also, when these people are given a special test to see how their regulatory feedback system is working, it seems that the stress hormone cascade is not switching itself off as well as it ought to, which means that their bodies are consistently being bombarded with higher than average levels of the stress hormones. Another interesting research finding is that if a depressed person is treated and gets better emotionally, but blood tests show that their stress hormone system remains over-reactive, they seem to be more likely to relapse sooner into another depression than if their stress system had righted itself. This has led scientists to suggest that depression leaves a sort of 'chemical scar' on the brain and body, by means of the stress hormone system. Find links to the quoted research studies at the bottom of this page. New research has begun to show that one of the ways in which antidepressant medication works is by helping the stress hormone system in the brain to function more optimally and to 'right' itself. Even more interestingly, some scientists are trying to see if genetic susceptibility to depression works through the mechanism of an inherent 'weakness' or inflexibility in the body's stress hormone system. They are measuring stress hormone activity in the never-depressed relatives of people who have had a depression, to see if there is some kind of pre-existing hormonal susceptibility to stress and depression within families. This new research is also important in that stress and depression are being looked at in PREGNANT WOMEN. Soon-to-be-published findings show that women who are depressed in pregnancy have higher than average levels of the stress hormones in their blood. This is over and above the high stress hormone levels that are already present normally in pregnancy. The theory is that high levels of stress and depression cause elevated levels of cortisol in a pregnant mother and, since cortisol crosses the placenta, these high levels of stress hormones act on baby's developing brain, possibly permanently 'setting' baby's stress hormone axis at a vulnerable level. This has yet to be proven directly. Click here to read more about the effects of stress and depression on unborn baby.
Below are the references for the research articles looking at the link between mental stress and depression through the stress hormone system.
1. PW Gold, GP Chrousos - Molecular Psychiatry, 2002 - nature.com 2. Lauer CJ et al, J Psychiatr Res. 1998 Nov-Dec;32(6):393-401 3. Carmine M Pariante, Journal of Neuroendocrinology, Volume 15 Page 811 - August 2003
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