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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:
Causes of depressionEdit
The etiology of mental disorders is best appreciated through a multidimensional integrative approach that disfavors reductionism and encourages models that consider a wide array of biological, psychological, and social forces. Two such models are the biopsychosocial model and the diathesis-stress model. In the biopsychosocial model, biological, psychological, and social factors all play a role in causing depression. There is overlap, and the precise causes vary depending on individual circumstances. The diathesis–stress model posits that depression results when a preexisting vulnerability, or diathesis, is activated by stressful life events. The predisposition can be either genetic, implying an interaction of nature and nurture, or schematic, involving a lasting influence of mental structures formed in childhood. This approach to understanding the causes of depression has garnered empirical support. For example, a prospective, longitudinal study uncovered a moderating effect of the serotonin transporter (5-HTT) gene on stressful life events in predicting depression. Specifically, depression seems especially likely to follow such events, but even more so in people with one or, worse yet, two short alleles of the 5-HTT gene. A Swedish study estimated the heritability of depression (the degree to which individual differences in occurrence are associated with genetic differences) to be approximately 40% for women and 30% for men.
- 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.
- 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.
- 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.
- Personality variablesLong standing patterns of thinking, feeling and behaviour that are related or contribute to personality have been linked as causes of depression
- Family relationships - Those living with someone suffering from depression experience increased anxiety and life disruption, increasing the possibility of also becoming depressed.
- 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
- 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." 
- 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).
- Neuroanatomy Recent research has suggested that there may be a link between depression and neurogenesis of the hippocampus.
- Hormonal factorsThe levels of hormones, the chemical messengers in the body that help regulate metabolism, have been linked to 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)."  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, 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.
- 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. This link has been at least partly validated by studies using dietary supplements in schools 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.
- 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." 
Up to 60% of people who suffer a [[stroke may experience depression in the first year .
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. 
- 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.
References & BibliographyEdit
- ↑ Barlow 2005, pp. 30-67
- ↑ Department of Health and Human Services (1999). The fundamentals of mental health and mental illness. (PDF) Mental Health: A Report of the Surgeon General. URL accessed on 2008-11-11.
- ↑ 3.0 3.1 Caspi A, Sugden K, Moffitt TE, et al. (2003). Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene. Science 301: 386–89.
- ↑ Haeffel GJ; Getchell M; Koposov RA; Yrigollen CM; DeYoung CG; af Klinteberg B; et al. (2008). Association between polymorphisms in the dopamine transporter gene and depression: Evidence for a gene-environment interaction in a sample of juvenile detainees. (PDF) Psychological Science. URL accessed on 2008-11-11.
- ↑ Slavich GM (2004). Deconstructing depression: A diathesis-stress perspective. APS Observer. URL accessed on 2008-11-11.
- ↑ Kendler KS, Gatz M, Gardner CO, Pedersen NL (January 2006). A Swedish national twin study of lifetime major depression. American Journal of Psychiatry 163 (1): 109–14.
- ↑ Manev, R, Manev H (2004). 5-Lipoxygenase as a putative link between cardiovascular and psychiatric disorders. Critical Reviews in Neurobiology 16 (1�2): 181�6.
- ↑ Lawrence, Felicity (2004). "The Ready Meal" Kate Barker Not on the Label, 214, Penguin. ISBN 0-141-01566-7.
- ↑ Using Fatty Acids for Enhancing Classroom Achievement. URL accessed on January, 2004.
- ↑ Omega-6 Levels in Brain Linked to Depression. URL accessed on May, 2006.