Hormones and the Endocrine System
Another area of research in determining the causes of clinical depression is focused on the endocrine system. This system works with the brain to control numerous activities within the body. The endocrine system is made up of small glands within the body, which create hormones and release them into the blood. The hormones that are released into the body by the glands regulate processes such as reaction to stress and sexual development. It has been found that a great number of people who are depressed have abnormal levels of some hormones in their blood despite having healthy glands. It is believed that such hormonal irregularities may be related to some depressive symptoms such as problems with appetite and sleeping since they play a part in these activities. Further clues to the role of the endocrine system has to do with the fact that those who have particular endocrine disorders sometimes develop depression, and some individuals who are depressed develop endocrine problems despite having healthy glands.
The endocrine system usually keeps the hormonal levels from becoming excessive through an intricate process of feedback, much like a thermostat in a home. Hormonal levels in the body are constantly monitored. When a specific hormone rises to particular level the gland stops producing and releasing the hormone. When an individual is depressed this feedback process may not function as it should.
Problems with hormone levels may be intertwined with the changes in brain chemistry that are seen in clinical depression. The endocrine system is connected with the brain at the hypothalamus which controls many bodily activities such as sleep, appetite, and sexual drive. The hypothalamus also regulates the pituitary gland that, in turn, controls the hormonal secretion of other glands. The hypothalamus uses some of the neurotransmitters that have been associated with depression as it manages the endocrine system. These neurotransmitters, serotonin, norepinephrine, and dopamine all have a role in the management of hormone function.
The development of clinical depression may be a symptom of a disorder present within organs that produce hormones. Such conditions include thyroid disorders, Cushing's syndrome, and Addison's disease.
Cortisol
Of those individuals who are clinically depressed, about one-half will have an excess of a hormone in their blood called cortisol. Cortisol is secreted by the adrenal glands. Located near the kidneys, the adrenal glands assist us in our reactions to stressful events. Cortisol may continue to be secreted even though a person already has high levels in his or her blood. This hormone is believed to be related to clinical depression since the high levels usually reduce to a normal level once the depression disappears.
The hypothalamus may be the culprit when it comes to excessive levels of cortisol in the blood. It is responsible for starting the process that leads to the secretion of cortisol by the adrenal glands. The hypothalamus first manufactures corticotrophic-releasing hormone (CRH). The pituitary gland is then stimulated into releasing adrenocorticotrophic hormone (ACTH). This hormone then makes the adrenal glands secret cortisol in the blood. When the endocrine system is functioning properly, the hypothalamus monitors the level of cortisol that is in the blood. When the level rises, the hypothalamus slows down its influence on the pituitary gland in production of CRH. When cortisol levels become reduced, the hypothalamus causes the pituitary gland to produce more CRH. In a person who is depressed, the hypothalamus may continuously influence the pituitary to produce CRH without regard to the amount of cortisol that is in the blood.
Other research concerning cortisol has shown that the timing of the release of this hormone may be problematic in those who are depressed. People who are not depressed tend to have secretions of cortisol at certain times of the day. Cortisol levels are highest at approximately 8:00 a.m. and 4:00 p.m., and then lowest during the night. This normal cycling of cortisol levels does not occur in some people who are depressed. For instance, they might have a consistent level of cortisol all the time, or highest amounts in the middle of the night.
Cortisol levels can be tested using something called a dexamethasone suppression test (DST). This is not a test for depression since some people who are depressed may not be identified by the results of the test, but it can be used to confirm a diagnosis of depression in some people. This test involves giving a dose of dexamethasone, a synthetic cortisol, to an individual before he or she goes to sleep at night. At 8:00 a.m. the next morning, the person's blood is tested for cortisol. It is tested again at 4:00 p.m. In healthy individuals cortisol levels drop at first, but then return to normal as the hypothalamus compensates for the dexamethasone in the blood. In those who are severely depressed, approximately one-half will have abnormal results. Cortisol secretion may not be reduced by the hypothalamus, or there may be no change at all after receiving the synthetic cortisol.
