Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behavior, feelings and sense of well-being. People with depressed mood can feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, ashamed or restless. They may lose interest in activities that were once pleasurable, experience loss of appetite or overeating, have problems concentrating, remembering details or making decisions, and may contemplate, attempt or commit suicide. Insomnia, excessive sleeping, fatigue, aches, pains, digestive problems or reduced energy may also be present.
Depressed mood is a feature of some psychiatric syndromes such as major depressive disorder, but it may also be a normal reaction to life events such as bereavement, a symptom of some bodily ailments or a side effect of some drugs and medical treatments.
Adversity in childhood, such as bereavement, neglect, unequal parental treatment of siblings, physical abuse or sexual abuse, significantly increases the likelihood of experiencing depression over the life course.
Life events and changes that may precipitate depressed mood include childbirth, menopause, financial difficulties, job problems, a medical diagnosis (cancer, HIV, etc.), bullying, loss of a loved one, natural disasters, social isolation, relationship troubles, jealousy, separation, and catastrophic injury.
Adolescents may be especially prone to experiencing depressed mood following social rejection.
Depressed mood can be the result of a number of infectious diseases, nutritional deficiencies, neurological conditions  and physiological problems, including hypoandrogenism (in men), Addison's disease, Lyme disease, multiple sclerosis, chronic pain, stroke, diabetes, cancer, sleep apnea, and disturbed circadian rhythm. It is often one of the early symptoms of hypothyroidism (reduced activity of the thyroid gland).
A number of psychiatric syndromes feature depressed mood as a main symptom. The mood disorders are a group of disorders considered to be primary disturbances of mood. These include major depressive disorder (MDD; commonly called major depression or clinical depression) where a person has at least two weeks of depressed mood or a loss of interest or pleasure in nearly all activities; and dysthymia, a state of chronic depressed mood, the symptoms of which do not meet the severity of a major depressive episode. Another mood disorder, bipolar disorder, features one or more episodes of abnormally elevated mood, cognition and energy levels, but may also involve one or more episodes of depression. When the course of depressive episodes follows a seasonal pattern, the disorder (major depressive disorder, bipolar disorder, etc.) may be described as a seasonal affective disorder.
Outside the mood disorders: borderline personality disorder often features an extremely intense depressive mood; adjustment disorder with depressed mood is a mood disturbance appearing as a psychological response to an identifiable event or stressor, in which the resulting emotional or behavioral symptoms are significant but do not meet the criteria for a major depressive episode;:355 and posttraumatic stress disorder, an anxiety disorder that sometimes follows trauma, is commonly accompanied by depressed mood.
Substance use disorder
Depressed mood may not require any professional treatment, and may be a normal reaction to certain life events, a symptom of some medical conditions, or a side effect of some drugs or medical treatments. A prolonged depressed mood, especially in combination with other symptoms, may lead to a diagnosis of a psychiatric or medical condition, e.g. of a mood disorder, which may benefit from treatment. Different sub-divisions of depression have different treatment approaches. In the United States, it has been estimated that two thirds of people with depression do not actively try to receive treatment.
The UK National Institute for Health and Care Excellence (NICE) 2009 guidelines indicate that antidepressants should not be routinely used for the initial treatment of mild depression, because the risk-benefit ratio is poor.
Deep brain stimulation (DBS) is a neurosurgical treatment which entails the application of a device into certain parts of the brain. This treatment is still undergoing controlled trials, but it is showing very promising results in regard to treatment for resistant depression.
Gender Differences in Depression
Within Depression there are a number of different symptoms that are used to help diagnose depression. If you look at all instances of Depression that can be confirmed (I.e. psychological help is obtained or a suicide occurs from depression related circumstances) women have a higher rate of depression, but if you break it down to individual symptoms the gender divide intensifies in some areas, disappears in some, and reverses in others. One place where the gender divide increases is in somatic symptoms, as defined as appetite and sleep disturbances and fatigue accompanied by pain and anxiety. However the gender difference was much smaller in other types of depression. The difference was female respondents reported twice the prevalence of somatic depression as male (2.8% vs. 1.4%) versus pure depression (2.3% vs. 1.7%) and somatic depression was highly likely to also have an anxiety disorder (31.4% vs. 22.9%), to have pain (60% vs. 48%), and to have chronic depression (49.2% vs. 36.8%). Men with somatic depression were more likely than those with depression to have pain (48.9% vs. 28.6%) but were not more likely to have an anxiety disorder (39.3% vs. 31.9%) or chronic dysphoria (37.8% vs. 33.3%). However, instances of Suicide in men is much greater than in women. In a report done by Stanford and Sweden, it was shown that men commit suicide almost three times that of women in Sweden, and the Centers for Disease Control and Prevention and National Center for Injury Prevention and Control reported that the rate in the US is almost four times as many males as females. However, it was found that women attempt suicide and have higher rates of suicide ideations. The difference between the two statistics is attributed to men choosing more permanent methods resulting in a higher rate of suicide completion
The most prevalent problem in analyzing the results of mental health research and mental health statistics is the prevalence of reporting bias. This is caused because the only way to currently collect data is to survey people and look at hospitalization rates. Because of this there are a lot of potential problems with people mis-reporting their feelings, frequency of depressive and anxious thoughts, and other pieces of information that subjects might want to suppress or might not realize are significant. This is exacerbated by cultural norms that encourage males not to express their feelings, and “tough it out” or deal with all emotion internally. It is also exacerbated by cultural norms that encourage women to express all of their emotions and share everything.
People also have a tendency to view mental illness as "all in your mind," with the preconception that if the person just tries hard enough they will be able to fix it. As a result of this, subjects tend to under report the prevalence of depressive or anxious episodes, men more so than women for the above reason. Subjects also tend to resist the idea that they might have a mental illness because "then something would be wrong about them" so they attempt to suppress any idea to the contrary on a survey. This is further complicated by societal stigmas against mental illnesses, and refusal to recognize them as "legitimate" illnesses. While, women are diagnosed with depression and anxiety statistically more than men, there is a lot of societal pressures on all genders to not report mental illnesses because they are afraid of being viewed as "crazy" or afraid of being judged as weak and powerless to control themselves. This leads to significant potential errors in the statistical analysis that has been done on the prevalence of internalized mental disorders, and potential errors in the differences experienced by genders. Finally, because of the nature of societal pressures, people suffering from mental disorders or suffered emotional trauma such as sexual assault or abuse often feel like nobody will support them even if they do report it resulting in learned helplessness. This happens to all genders, but it is hypothesized that different genders and gender identities are affected disproportionately depending on the specific situation.
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