Black thoughts. Don't want to think anymore. Can't stop this vortex in my mind. Thoughts of death, unwanted, uninvited, force their way into my consciousness. Go away . . . go away...leave me be, I cry.

Biological Causes

Biological factors contribute to or cause a large percentage of depression. Emotional stability is closely related to the normal formation and function of a number of vital chemicals that exist in the brain. These chemicals are called neurotransmitters and are a very important part of the system that transmits information from one brain cell to another. When brain cells lose the ability to make the proper amount of neurotransmitters or cannot store them properly, chronic depression can result. 

       
There are three physiological conditions that can affect the production and functions of neurotransmitters. 

Specific Diseases
Hormonal Imbalances
Genetic Factors

 

Diseases That Affect Neurotransmitter Production
 
As many diseases progress, they can slowly change the chemistry of your body. The delicate balance of brain chemistry can be altered enough to generate a mood shift, even before physical symptoms are apparent. 
 
Diseases of the central nervous system, such as Alzheimer's and Multiple Sclerosis can affect brain chemistry since these diseases are actually located in the brain. 

Many infectious diseases can generate psychiatric symptoms, such as mononucleosis and infectious hepatitis. 

Diseases of the immune system can also be the source of a wide array of psychiatric symptoms. Lupus, allergies, and AIDS are just three examples of immune system diseases that can cause depression. 

  Hormonal Imbalances
Hormones are released into the bloodstream by the endocrine glands. Hormones keep the body in a state of balance by regulating metabolic processes such as growth, sexual development, reproduction, sexual activity, heart rate, and blood pressure. The entire endocrine system is intimately linked to the nervous system. For example, norepinephrine, a neurotransmitter that is very important for mood stability can also double as a hormone secreted by the adrenal gland. 

The thyroid gland, which secretes two crucial hormones, is probably the most common biological cause for depression. It is estimated that between 10 and 15 percent of depressed persons have some form of thyroid disorder. 


Diseases of the adrenal glands are not as common as those of the thyroid, but can still cause depression. The entire endocrine system can be affected by malfunctions of the pituitary gland, and psychiatric symptoms are present in three-quarters of all cases. Since this gland is directly linked to the hypothalamus and the limbic system, anything that alters it's function is likely to affect one's emotional state. 

Sex hormones, particularly the female hormones, estrogen and progesterone, are often implicated in depression. Depressive symptoms are common among women who are pre-menstrual, pregnant, postpartum, or pre-menopausal. 

 

       

Genetic Factors 

  

Depression tends to run in families, so genetics may be a factor; however, the role genetics plays is not clearly defined. Not all children of depressed parents suffer from depression.
       

Psychological Causes
About 25 percent of people suffering from depression report experiencing severe stress. Studies show that people who have had a loved one die when they were young are at least twice as likely to suffer from an episode of major depression when they are adults as someone who has not experienced the same type of loss. There seems to be a clear link of some kind between stress and depression, although such it has not been clinically proven that stress causes major depression. 

Post-traumatic stress disorder also seems to have a link to depression. Fifty percent of persons suffering from post-traumatic stress disorder also suffer from depression.