Chronic Illness
While any type of physical illness can affect mood, chronic illness is most likely to cause clinical depression. Examples of chronic illness include arthritis, cancer, colitis, kidney disease, diabetes, heart disease, HIV/AIDS, lupus and multiple sclerosis. The illness can aggravate the depression, and the depression can aggravate the illness.
The Endocrine System
The endocrine system is composed of a variety of hormone-secreting glands. Certain illnesses can cause endocrine disorders, which may eventually lead to depression. For example, diabetes, as well as certain cancerous and benign tumors can cause Cushing's Syndrome. This hormonal disorder causes the endocrine system to increase its secretion of cortisol, which is a stress hormone. Depression is one of the side effects of Cushing's syndrome.
Certain brain tumors can also cause hypopituitarism, which can in turn lead to an under-active thyroid. This condition may lead to depression.
Psychological Factors
A number of psychological factors may be associated with depression caused by illness. Excessive weight loss or weight gain may have a significant influence on body image. The inability to work and perform normal daily functions can cause low self-esteem. Gastrointestinal disorders may cause self-disgust. The financial strains associated with chronic illness can make the patient feel guilty about the stress placed on his or her family. Terminal illnesses can contribute to a sense of gloom and doom.
Medication and Depression
The medications used to treat specific illnesses may alter the brain chemistry and cause depression. While the mechanisms of the medication/depression link are unclear, researchers have speculated that these drugs might decrease the availability of serotonin, which is a mood-regulating neurotransmitter. For example, certain anti-anti-tuberculosis medications can interfere with the body's use of B6. B6 plays an important role in the production of serotonin.
Decreased Physical Activity
The effects of aerobic exercise on mood have been well documented. In fact, a study performed at the Department of Psychiatry and Behavioral Sciences at Duke University Medical Center found that exercise may be more effective than the anti-depression drug Zoloft for the treatment of depression.
Certain illnesses can cause a once-active person to decrease her physical activity level. This would have an obvious effect on the brain chemistry. One can speculate that this may lead to depression.
