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Depression is a state of low mood and aversion to activity. Some consider it a dysfunction, while others see it as an adaptive defense mechanism. The Diagnostic and Statistical Manual of Mental Disorders defines a depressed person as experiencing feelings of sadness, helplessness and hopelessness. In traditional colloquy, feeling "depressed" is often synonymous with feeling "sad", but both clinical depression and non-clinical depression can also refer to a conglomeration of more than one feeling.

The precise number of individuals who have severe depression are not known but estimates indicate that about 12 million adults in the US have depression. Depression cuts across all barriers and affects all races, cultures and social classes. The disorder generally begins in early adulthood but can occur at any age. While hospital data reveal that more women have depression, it is hypothesized that this is because men are less likely to seek treatment. Depression occurs in various grades and symptoms are likely to vary in intensity.

Slight depression is of minor consequence. One may become slightly depressed over a loss of a job; break up of a romantic relationship or divorce. Other causes of slight depressions include loss of a parent, sibling, marital stress, job anxiety, moving or not having a great job. Slight depression may present with feelings of sadness, sleeping problems, irritability, being easily annoyed and feeling tired. Slight depression is reversible and short term. Most people get over slight depression with time and supportive therapy.

There are some individuals whom may develop mild depression, which may start gradually for no reason. The individual may start to feel tired, restlessness, loneliness and have difficulty sleeping. In many cases, the individual loses interest in sex and wants to be left alone. One may be able to go to work but not have any enjoyment. Mild depression may last a lot longer than slight depression, but can be overcome with changes in lifestyle, psychotherapy and social support. [1]

However, some individuals develop severe depression, which may induce feelings of suicidal ideation as it is common in severe depression. In severe depression, one may feel sad constantly, cry for no apparent reason, have trouble sleeping and focusing , become fatigued, feel worthless, have headaches or even backache . [2] While slight depression has a cause, both mild and severe depression generally are complex disorders, which are not well understood. Mild depression may be related to the environment, such as being unable to cope with a certain job, unemployment, financial problems or loss of a loved one. No one understands why severe depression occurs. Even though many brain imaging studies have been done, the exact neurotransmitters in the brain which play a role in depression are still in question. Some studies do show that severe depression may be more common in families. [3] Although the exact causes of depression are unknown, there are several risk factors that can trigger or increase the risk of depression. [4]



There are many symptoms that signify depression. The frequency, duration, and severity of these symptoms will vary depending on the individual. [5] Some signs and symptoms that can occur include:[6][7]

  • Anger and/or irritability.
  • Persistent sadness, the feeling of being "empty", and anxious.
  • Changes in sleep patterns (insomnia, in particular during the early hours of the morning, or oversleeping which is also known as hypersomnia).
  • Loss of interest in everyday activities.
  • Appetite or weight changes (a significant weight gain or loss, by more than 5% of body weight).
  • Irritability or restlessness.
  • Loss of energy.
  • Concentration problems.
  • Fear of failure.
  • Repetition in speech.
  • Unexplained aches and pains.
  • Frequent thoughts of suicide or death.
  • Compulsive-obsessive disorders (such as chewing fingernails).
  • Inability to control spending or eating.
  • Feeling worthless or ignored.


It is estimated that about 1 out of 6 adults suffer from depression.[8] Although depression does not have a single cause, many things contribute to the feeling of depression, such as family history, pessimistic personality, trauma and stress, physical conditions, and other psychological disorders. [9] Gender may additionally be a contributing factor. Women and men may experience depression in different ways. [10]

Risk factors

  • Having a family member or relative with depression.
  • Having a family member who has committed suicide.
  • Stressful events like losing a job, death of a loved one, financial difficulties.
  • Having depression as a child or teenager.
  • Having a chronic illness like heart disease, Alzheimer's disease, AIDS, or cancer.
  • Having a personality where one has low self-esteem, no confidence, being dependent on others or being criticized all the time.
  • Having just delivered a baby (postpartum depression).
  • Having little or no money and being of a low socioeconomic status.

Slight and mild depression may not cause any complications. But severe depression can have an agonizing toll on the individual and the family. When severe depression is untreated it can quickly lead to disability and suicidal thinking. Severe depression can also cause deep emotional turmoil, changes in behavior, and legal and monetary problems. [11]

Biological influences of depression are varied, but may relate to malnutrition, heredity, hormones, seasons, stress, illness, drug or alcohol use, neurotransmitter malfunction, long-term exposure to dampness and mold,[12] back injury, and to aerosol exposure.[13][14] There are also correlations between long term sleep difficulties and depression. Up to 90% of patients with depression are found to have sleep difficulties.[15]


When depression is neglected or severe, it can lead to:

  • Suicide.
  • Substance abuse.
  • Alcoholism.
  • Anxiety.
  • Heart problems.
  • Weight problems.
  • Work-related problems.
  • Family conflicts.
  • Interpersonal difficulties.
  • Social isolation and loneliness.


There exists a number of different treatments for depression: Antidepressants include clinical drugs like Prozac and herbal remedies like St John's Wort. Physical activity has been linked to the increase in blood serotonin after exercise, similar to the effects of selective serotonin reuptake inhibitors (SSRI).[16] Research published by the American Medical Association concludes: Findings are consistent with a beneficial effect of physical activity on feelings of sadness and suicidal behaviors in Hispanic and non-Hispanic white boys and girls.[17] Various initiatives promote dialogue and non-drug therapy, arguing that drugs should be only used as last resort in cases of depression. R U OK Day, an Australian initiative promoting depression awareness and dialogue, received nationwide media coverage at its inauguration on 29th November 2009[18]

As a defense mechanism

A number of authors have suggested that depression is an evolutionary adaptation. A low or depressed mood can increase an individual's ability to cope with situations in which the effort to pursue a major goal could result in danger, loss, or wasted effort.[19] In such situations, low motivation may give an advantage by inhibiting certain actions. This theory helps to explain why depression is so prevalent, and why it so often strikes people during their peak reproductive years. These characteristics would be difficult to understand if depression were a dysfunction, as many psychiatrists assume.[19]

Depression is a predictable response to certain types of life occurrences, such as loss of status, divorce, or death of a child or spouse. These are events that signal a loss of reproductive ability or potential, or that did so in humans' ancestral environment. Depression can be seen as an adaptive response, in the sense that it causes an individual to turn away from the earlier (and reproductively unsuccessful) modes of behavior.

A depressed mood is common during illnesses, such as influenza. It has been argued that this is an evolved mechanism that assists the individual in recovering by limiting his/her physical activity.[20] The occurrence of low-level depression during the winter months, or seasonal affective disorder, may have been adaptive in the past, by limiting physical activity at times when food was scarce.[20] It is argued that humans have retained the instinct to experience low mood during the winter months, even if the availability of food is no longer determined by the weather.[20]

An alternative theory [21] posits that depression is a plea for help. However this view is not widely credited by evolutionary biologists: depression is observed in other species that are not social, and depression in humans is often actively hidden from others; even when it is apparent, it often fails to elicit a positive response.[22]

Milder depression has been associated with what has been called depressive realism, or the "sadder-but-wiser" effect, a view of the world that is relatively undistorted by positive biases.[23]

Psychiatric disorders

Episodes of depressed mood are a core feature of the following psychological disorders, as specified by the DSM-IV:

See also


  1. ^ Depression and major depression definition Mayo Clinic. Retrieved on 2010-02-07
  2. ^ Depression causes and treatment MedicineNet. Retrieved on 2010-02-07
  3. ^ What is depression National institute of mental health. Retrieved on 2010-02-07
  4. ^ Depression overview netDoctor Portal. Retrieved on 2010-02-07
  5. ^ Depression, National Institute of Health, 23 September 2009.
  6. ^ Depression, National Institute of Health, 23 September 2009.
  7. ^ Understanding Depression: Signs, Symptoms, Causes, and Help, Understand, Prevent and Resolve Life's Challenges.
  8. ^ Add-on Depression treatment, Otsuko America Pharmaceutical, Inc., July 2009
  9. ^ Understanding Depression, GlaxoSmithKline, 1997-2009.
  10. ^ Depression, National Institute of Health, 23 September 2009.
  11. ^ Depression Facts and Causes eMedicine Health Portal. Retrieved on 2010-02-07
  12. ^ Edmond D. Shenassa, Constantine Daskalakis, Allison Liebhaber, Matthias Braubach, and MaryJean Brown (2007). "Dampness and Mold in the Home and Depression: An Examination of Mold-Related Illness and Perceived Control of One’s Home as Possible Depression Pathways". American Journal of Public Health 97 (10): 1893. doi:10.2105/AJPH.2006.093773. PMID 17761567. PMC 1994167. 
  13. ^ Farrow, Alexandra (2003). "Symptoms of mothers and infants related to total volatile organic compounds in household products". Arch Environ Health 58 (10): 633–41. doi:10.3200/AEOH.58.10.633-641. PMID 15562635. 
  14. ^ Air fresheners can make mothers and babies ill, University of Bristol press release issued 19 October 2004
  15. ^ Roth T (2005). "Prevalence, associated risks, and treatment patterns of insomnia". J Clin Psychiatry 66 Suppl 9: 10–3; quiz 42–3. PMID 16336036. 
  16. ^ Wipfli B, Landers D, Nagoshi C, Ringenbach S (01). "An examination of serotonin and psychological variables in the relationship between exercise and mental health.". Scandinavian journal of medicine & science in sports (Denmark: Munksgaard International Publishers) 31 (1): 19-26. 9111504. ISSN 0905-7188. PMID 20030777. 
  17. ^ Brosnahan J, Steffen LM, Lytle L, Patterson J, Boostrom A (01). "The relation between physical activity and mental health among Hispanic and non-Hispanic white adolescents.". Archives of pediatrics & adolescent medicine (United States: American Medical Association) 158 (8): 818-923. 9422751. ISSN 1072-4710. PMID 15289257. 
  18. ^ Larkin, Gavin (2009). "Three words, one question, a life changed". Sunday Telegraph and Sunday Herald Sun.
  19. ^ a b Nesse R (2000). "Is Depression an Adaptation?". Arch. Gen. Psychiatry 57 (1): 14–20. doi:10.1001/archpsyc.57.1.14. PMID 10632228. 
  20. ^ a b c Why We Get Sick: The New Science of Darwinian Medicine, Randolphe M. Nesse and George C. Williams | Vintage Books | 1994 | ISBN 0-8129-2224-7
  21. ^ How Sadness Survived: The Evolutionary Basis of Depression, Paul Keedwell | Radcliffe Publishing | 2008 | ISBN 1846190134
  22. ^ Hendrie C A (2009). "Depression as an evolutionary adaptation: implications for the development of preclinical models.". Med. Hypotheses 72 (3): 342–347. doi:10.1016/j.mehy.2008.09.053. PMID 19153014.  PMID 19153014
  23. ^ Taylor, SE (1991). Positive Illusions: Creative Self-deception and the Healthy Mind. New York, NY, USA: Basic Books. ISBN 0465060536. 

External links

Simple English

In psychology, depression is a mood where a person is very sad. Depression may also mean a person has learned helplessness or is not interested in anything (disinterest). Depression that lasts a long time is called major depressive disorder. This can be a very serious mental illness when not taken care of.

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