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Main article: Clinical depression

In this section we will concentrate on the evidence for the causes of depression. For a broader treatment of the theoretical approaches to the condition see

Main article: Theoretical_approaches to depression:

[edit] Causes of depression

No single specific cause for depression has been identified, but a number of factors are believed to be involved. In any individual it is likely that a number of causes will have combined in the development of a clinical level of depression

[edit] Psychological factors

• Cognitive factors – Low self-esteem and self-defeating or distorted thinking are connected with depression. Although it is not clear which is the cause and which is the effect, it is known that depressed persons who are able to make corrections in their thinking patterns can show improved mood and self-esteem. Psychological factors related to depression include the complex development of one's personality and how one has learned to cope with external environmental factors such as stress.

Main article: Cognition and depression

• Early experiences - Events such as the death of a parent, abandonment or rejection, neglect, chronic illness, and physical, psychological, or sexual abuse can also increase the likelihood of depression later in life. Post-traumatic stress disorder (PTSD) includes depression as one of its major symptoms.

Main article: Early life experience and depression

• Recent life event - Job loss, financial difficulties, long periods of unemployment, the loss of a spouse or other family member, divorce or the end of a committed relationship, or other traumatic events may trigger depression. Long-term stress at home, work, or school can also be involved.

Main article: Clinical depression and life events

• Personality variablesLong standing patterns of thinking, feeling and behaviour that are related or contribute to personality have been linked as causes of depression

Main article: Personality and depression

[edit] Environmental factors

• Family relationships - Those living with someone suffering from depression experience increased anxiety and life disruption, increasing the possibility of also becoming depressed.

Main article: Family relationships and depression

• Seasonal affective disorder (SAD) is a type of depressive disorder that occurs in the winter when daylight hours are short. It is believed that the body's production of melatonin, which is produced at higher levels in the dark, plays a major part in the onset of SAD and that many sufferers respond well to bright light therapy, also known as phototherapy.

• Social environment - Factors such as poverty, unemployment, chronic stress at work have been suggested as causes of depression

Main article: The social context of depression

[edit] Biological causes

• Heredity - The tendency to develop depression may be inherited; there is some evidence that this disorder may run in families. A 2004 press release from the National Institute of Mental Health declares "major depression is thought to be 40-70 percent heritable, but likely involves an interaction of several genes with environmental events." [1]

Main article: Genetic factors in depression

Brain chemicals called neurotransmitters allow electrical signals to move from the axon of one nerve cell to the neuron of another. A shortage of neurotransmitters impairs brain communication.

• Neurochemical There may be changes or imbalances in chemicals that transmit information in the brain, called neurotransmitters. Many modern antidepressant drugs attempt to increase levels of certain neurotransmitters, such as serotonin and norepinephrine. Although the causal relationship is unclear, it is known that antidepressant medications can relieve certain symptoms of depression, although critics point out that the relationship between serotonin, SSRIs, and depression usually is typically greatly oversimplified when presented to the public (see here).

Main article: Neurochemistry of depression

• Neuroanatomy Recent research has suggested that there may be a link between depression and neurogenesis of the hippocampus.

Main article: Neuroanatomy of depression

• Hormonal factorsThe levels of hormones, the chemical messengers in the body that help regulate metabolism, have been linked to depression

Main article: Endocrinology of depression

• Postpartum depression (also known as postnatal depression) – Dr. Ruta M Nonacs writes that while many women experience some mood changes after giving birth, "10-15% of women experience a more disabling and persistent form of mood disturbance (eg, postpartum depression, postpartum psychosis)." [2] When it occurs, the onset typically is within three months after delivery, and it may last for several months. About two new mothers out of a thousand experience the more serious depressive disorder Postnatal Psychosis which includes hallucinations and/or delusions.

• Medical conditions – Certain illnesses, including cardiovascular disease^[1], hepatitis, mononucleosis, hypothyroidism, and organic brain damage caused by degenerative conditions such as Parkinson disease or by traumatic blunt force injury may contribute to depression, as may certain prescription drugs such as birth control pills and steroids. Gender dysphoria can also cause depression.

Main article: Depression and physical illness

• Nutrition – The increase in depression in industrialised societies has been linked to diet, particularly to reduced levels of omega-3 fatty acids in intensively farmed food and processed foods^[2]. This link has been at least partly validated by studies using dietary supplements in schools^[3] and by a double-blind test in a prison. An excess of omega-6 fatty acids in the diet was shown to cause depression in rats^[4].

Main article: Nutrition and depression

• Alcohol and other drugs – Alcohol can have a negative effect on mood, and misuse of alcohol, benzodiazepine-based tranquilizers, and sleeping medications can all play a major role in the length and severity of depression. The link between frequent cannabis use and depression is also widely documented, although the direction of causality remains in question; Dr. Salynn Boyles writes, "...research has linked pot smoking with depression and schizophrenia ... daily use [of marijuana] was associated with a five-fold increase in later depression and anxiety among young women. But depression and anxiety were not predictive of later marijuana use." [3]

Drug abuse and depression

[edit] Evolutionary theories

Evolutionary theory suggests that depression is a protective mechanism: If an individual is involved in a lengthy fight for dominance of a social group and is clearly losing, depression causes the individual to back down and accept the submissive role.  In doing so, the individual is protected from unnecessary harm.  In this way, depression helps maintain a social hierarchy.

• Other evolutionary theories – Another evolutionary theory is that the cognitive response that produces modern-day depression evolved as a mechanism that allows people to assess whether they are in pursuit of an unreachable goal. Still others claim that depression can be linked to perfectionism. People who accept satisfactory outcomes in lieu of "the best" outcome tend to lead happier lives. ^{[citation needed]}

• Recently some evolutionary biologists have begun to subscribe to the theory of "honest signalling". It has been pointed out that the incidence of major depression is much higher in persons born after 1945 which would seem to cast doubt on a possible disease model and that such suffering is notable in persons of greater than average intellect and emotional complexity. This contradicts the submission thesis.

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