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Depression, a common and debilitating condition that can affect up to 14.8 million Americans, or 7 percent of the population, in any given year, has no single cause. The condition cannot be predicted, and it strikes people in all walks of life. However, depression is more likely to occur in certain people. The causes of depression may be biological, social and environmental.
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Causes of Depression: The Brain
People with depression seem to have certain brain abnormalities, although researchers aren't sure what caused them. Brain scans, such as magnetic resonance imaging (MRI), have shown that the brains of people with depression appear different than those of people without depression. Specifically, the portions of the brain that control mood, thinking, sleep, appetite and behavior seem to function abnormally. Still, no standardized tool for diagnosing or treating depression based on imaging studies exists.
People with depression may also have unbalanced neurotransmitters, chemical messengers in the brain that affect mood and behavior. Neurotransmitters that have been implicated in the prognosis of depression include serotonin, acetylcholine, dopamine, norepinephrine, epinephrine, and corticotropin-releasing factor, a stress hormone.
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Depression tends to run in families, although it may appear in people without a family history of depression. Close relatives of people with depression are two to six times more likely to develop the condition than individuals without a family history, according to Harvey Simon, MD, Associate Professor of Medicine at Harvard Medical School.
A gene called MPK-1 is twice as active in people with depression, according to a 2010 study led by Vanja Duric of Yale University and published in Nature Medicine. It acts as an 'on-off' switch which controls MAPK, a signaling pathway in the brain. The increased expression of the gene may alter the growth and function of neurons in the brain's hippocampus, which are known to lead to symptoms of depression. While genetics may predispose some people to depression, the condition may not occur until it is triggered by certain life events.
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Causes of Depression: Hormones
A disruption in the body's natural hormone balance may trigger depression in some women. For example, premenstrual dysphoric disorder can cause depression symptoms. Hormone changes in expectant mothers can trigger depression during pregnancy or postpartum depression. Women going through menopause may also be at increased risk of depression, especially if they've previously suffered from the condition. Hormonal changes due to thyroid problems can also result in depressive symptoms.
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Traumatic events, such as sexual abuse or assault, divorce or the death of a loved one, may trigger depression in genetically-vulnerable people. Chronic stress, due to poverty, illness, social isolation, relationship dissatisfaction or work/life balance, may also increase risk. Often, different situations combine to create the causes of depression. Societal and cultural expectations can also be damaging to some people. Media images that demonize homosexuality can create feelings of shame and isolation in some people who are homosexual. Cultural expectations of thinness can be damaging to young women with developing bodies.
Certain medications, including those used for acne, high blood pressure, contraception, Parkinson’s disease, inflammation and gastrointestinal relief, can trigger depression in susceptible people. The use of alcohol and drugs can also exacerbate risk.