The Biology of Depression.

Depression is a common and potentially devastating illness. As reported in "Archives of
General Psychiatry" in 2005, depression affects approximately 14.8 million or 6.7% of
American adults. In 1996 the US Department of Health and Human Services noted that 1
out of 33 children and 1 out of 8 adolescents have clinical depression. According to the
World Health Organization, untreated depression is the leading cause of disability in
people aged 15­44 and is the cause of 2/3 of the suicides in the United States.

Despite its prevalence in our society, depression is still not well accepted or understood
by many people as a true medical illness. The purpose of this article is to give an
overview of the biological basis for depression and help explain why depression is a
medical illness that requires treatment.

The human body likes to be in “homeostasis”. That term roughly means balance.
Medical illness is often caused by an imbalance; for example in diabetes insulin levels are
low which causes an imbalance in the affected person’s blood sugar. When the
imbalance is severe enough, that person begins to suffer from the effects of it. In
diabetes, high blood sugar due to low insulin can cause weakness, increased hunger or
thirst and increased urination among other things. With depression, an imbalance in
certain neuro­chemicals in the brain cause, among other problems, a depressed and sad
feeling, loss of enjoyment, loss of interest, guilty and hopeless feelings, low energy,
irritability, low motivation, poor concentration, decreased appetite, and suicidal
thoughts. Everybody presents differently when they are depressed, with a different
severity and array of symptoms. This is because, like with any illness, the severity is
based on factors like genetic risk, health of the person, and stressors. The wide variety of
symptoms of depression is due to the fact that many different areas of the brain rely on
neuro-­chemicals for normal function; they are affected in different ways in each person.

The main neuro­-chemicals in the brain implicated in depression include Serotonin,
Norepinephrine and Dopamine. Together, these are referred to as the “Monoamines”.
Monoamine levels are low in people with depression and this imbalance has led to the
primary hypothesis for the cause of depression; the “Monoamine Hypothesis”. It is not
entirely clear why the imbalance causes depression, but there are two reasons this
remains to be the leading theory behind depression. First, studies that compare
monoamine levels in depressed subjects versus non­depressed subjects consistently
demonstrate lower levels of monoamines in the depressed subjects. Second, when a
clinically depressed person takes a medication that raises the levels of the monoamines
that person often feels better and the symptoms are mitigated or resolved; a balance in the
monoamines is restored.

Low levels of monoamines or low sensitivity to monoamines can be caused by many
different insults or stressors. A list of common stressors includes genetic risk, certain
medical illnesses, drug use, relational problems, history of abuse and/or neglect, and
work/financial problems. As each person is unique, however, the list of possible stressors
is infinite.

As you can see, depression does have a strong physiologic basis. This is why, like in any
medical illness, treatment for depression is important for recovery. Because of the nature
of depression, the treatment is best when it involves therapy and support to address
stressors as well as medications to restore balance.