Causes of depression

    * Physiology – There may be changes or imbalances in chemicals that transmit information in the brain, called neurotransmitters. Many modern antidepressant drugs increase levels of certain neurotransmitters, such as serotonin and norepinephrine(noradrenaline). 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). Recent research has suggested that there may be a link between depression and neurogenesis of the hippocampus.[citation needed] This horseshoe-shaped structure is a center for both mood and memory. Loss of neurons in the hippocampus is found in depression and correlates with impaired memory and dysthemic mood. The hippocampus regains mass when exposed to treatments that increase brain serotonin, and when regrown, mood and memory tend to be restored.

    * 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.

    * Psychological 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.[citation needed] 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.[citation needed]

    * 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.

    * Life experiences – Job loss, poverty, financial difficulties, gambling addiction, long periods of unemployment, the loss of a spouse or other family member, divorce or the end of a committed relationship, involuntary celibacy, or other traumatic events may trigger depression. Long-term stress at home, work, or school can also be involved. Bullying in late adolescence is also thought to be a contributing factor.

    * Medical conditions – Certain illnesses, including cardiovascular disease,[11] hepatitis, mononucleosis, hypothyroidism, and organic brain damage caused by degenerative conditions such as Parkinson disease, Multiple Sclerosis or by traumatic blunt force injury may contribute to depression, as may certain prescription drugs such as hormonal contraception methods and steroids. Gender dysphoria can also cause depression.

    * Diet – 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.[12] This link has been at least partly validated by studies using dietary supplements in schools[13] 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.[14]

    * 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.

    * 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 (e.g., 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.

    * Living with a depressed person – Those living with someone suffering from depression experience increased anxiety and life disruption, increasing the possibility of also becoming depressed.[citation needed]

    * Evolutionary biological hypotheses of depression – Evolutionary analyses usually consider possible functions for depressed mood as well as clinical depression.

        * The psychic pain hypothesis: psychic pain, such as depression, is analogous to physical pain. The function of physical pain is to inform the organism that it is suffering damage, to motivate it to withdraw from the source of damage, and to learn to avoid such damage-causing circumstances in the future. Analogously, depression informs the sufferer that current circumstances, such as the loss of a mate, are imposing a threat to biological fitness, it motivates the sufferer to cease activities that led to the costly situation, if possible, and it causes him or her to learn to avoid similar circumstances in the future. Proponents of this view tend to focus on low mood, and regard clinical depression as a dysfunctional extreme of low mood. See, e.g., Nesse 2000 and Keller and Nesse 2005; see also Hagen and Barrett n.d..

        * Rank theory: If an individual is involved in a lengthy fight for dominance in 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. This theory is a special case of a more general theory derived from the psychic pain hypothesis: 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, and if they are, to motivate them to desist. See, e.g., Nesse 2000.

        * Honest signaling theory: When social partners have conflicts of interest, 'cheap' signals of need, such as crying, might not be believed. Biologists and economists have proposed that signals with inherent costs can credibly signal information when there are conflicts of interest. The symptoms of major depression, such as loss of interest in virtually all activities and suicidality, are inherently costly, but, as costly signaling theory requires, the costs differ for individuals in different states. For individuals who are not genuinely in need, the fitness cost of major depression is very high because it threatens the flow of fitness benefits. For individuals who are in genuine need, however, the fitness cost of major depression is low because the individual is not generating many fitness benefits. Thus, only an individual in genuine need can afford to suffer major depression. Major depression therefore serves as an honest, or credible, signal of need. See, e.g., Hagen 2003, Watson and Andrews 2002.

        * Social navigation or niche change theory: The social navigation, bargaining, or niche change hypothesis [3] suggests that depression, operationally defined as a combination of prolonged anhedonia and psychomotor retardation or agitation, provides a focused sober perspective on socially imposed constraints hindering a person’s pursuit of major fitness enhancing projects. Simultaneously, publicly displayed symptoms, which reduce the depressive's ability to conduct basic life activities, serve as a social signal of need; the signal's costliness for the depressive certifies its honesty. Finally, for social partners who find it uneconomical to respond helpfully to an honest signal of need, the same depressive symptoms also have the potential to extort relevant concessions and compromises. Depression’s extortionary power comes from the fact that it retards the flow of just those goods and services such partners have come to expect from the depressive under status quo socioeconomic arrangements.

          Thus depression may be a social adaptation especially useful in motivating a variety of social partners, all at once, to help the depressive initiate major fitness-enhancing changes in their socioeconomic life. There are extraordinarily diverse circumstances under which this may become necessary in human social life, ranging from loss of rank or a key social ally which makes the current social niche uneconomic to having a set of creative new ideas about how to make a livelihood which begs for a new niche. The social navigation hypothesis emphasizes that an individual can become tightly ensnared in an overly restrictive matrix of social exchange contracts, and that this situation sometimes necessitates a radical contractual upheaval that is beyond conventional methods of negotiation. Regarding the treatment of depression, this hypothesis calls into question any assumptions by the clinician that the typical cause of depression is related to maladaptive perverted thinking processes or other purely endogenous sources. The social navigation hypothesis calls instead for a penetrating analysis of the depressive’s talents and dreams, identification of relevant social constraints (especially those with a relatively diffuse non-point source within the social network of the depressive), and practical social problem-solving therapy designed to relax those constraints enough to allow the depressive to move forward with their life under an improved set of social contracts.