Depression has been part of the human condition since antiquity. Hippocrates, the ancient Greek "Father of Medicine," is generally credited with the first description of an emotional disorder and is thought to have coined the term "melancholia," literally translated as "black bile."(1)

Although life is filled with unexpected events such as the death of a loved one, loss of a job, major illness, or other catastrophic events, not everybody becomes depressed. Most individuals suffer only temporary feelings of depression and find ways to adjust to life's challenges. However, there are certain individuals who experience a major depressive episode when faced by stressful situations.

Depression has been classified as a mood disorder or "affective" disorder. Mood is defined as a powerful, sustained emotion that, in the extreme, markedly affects a person's perception of the world and ability to adequately function in society.(2) Mood disorders are among the most common health problems doctors see every day. Mood disorders are divided into two major categories: depressive disorders and bipolar disorders.

Depression affects approximately 5 percent of the population at any given time, and about 30 percent of adults will suffer from depression over a lifetime.(3) Commonly thought of as a disorder of young to middle adulthood, with an average age of onset in the late 20's, depression is also a common psychiatric illness in the elderly.(4) Women are two to three times more likely to experience depression than men.(3)

Mood disorders, depression, and anxiety are common illnesses in our society. Lost work time, family conflicts, personal strife, and other consequences of the disease can eventually lead to complete disruption of one's life. Depression and mood disorders have become increasingly recognized as widespread health problems. In spite of this they are often under-diagnosed and under-treated.(5)

The causes of depression are too complex to be totally explained by a single social, biological, or developmental theory. Several factors seem to work together to trigger depressive disorders. Heredity does seem to have a role, as studies have shown. Depressive disorders and suicide tend to run in families, and first-degree relatives of patients with depression are one and one half to three times more likely to develop depression than people with no depression in the immediate family.(6)

Depression is not simply "all in the head." Depression has physical causes, linked to abnormalities in brain chemistry. The symptoms of major depression consistently reflect changes in "neurotransmitters," substances that regulate function of the brain and nervous system. The neurotransmitters closely related to depression are norepinephrine, serotonin, and dopamine.(7)

Serotonin is a key neurotransmitter for maintaining mental and emotional health. Low serotonin plays a big role in depression. Prolonged stress—physical, mental, or emotional can deplete the body's serotonin supply. A host of other health problems can contribute to depression by robbing serotonin, including adrenal exhaustion, hypothyroidism, heavy metal toxicity, and "leaky gut" syndrome with subsequent food intolerance. Deficiencies in nutrients such as vitamin B12, folic acid, and certain amino acids can also be involved.