What is depression?

Depression^[1] is a medical condition that affects a person's thoughts and feelings as well as the body. It can be associated with various physical problems in areas such as sleep, appetite, energy, libido, and thinking. Research increasingly demonstrates that depression is not a condition resulting from personal or moral weakness but is a treatable illness. Although it is often associated with feelings of sadness or the "blues," it is not the same thing. The best way to characterize clinical depression from normal sadness is to think of the term depression in a global, bodily sense, where there is a reduction in physiologic^[2] activity across a variety of physical systems, including emotion and cognition. Although stressors^[3] can trigger an episode of depression, the stressful life event alone does not cause the condition. Anyone is susceptible to depression,

Research increasingly demonstrates that depression is not a condition resulting from personal or moral weakness but is a treatable illness.

although certain populations are at a higher risk. Untreated, depression can last for weeks, months, or years. Many people have recurrent episodes. As with any illness, both morbidity and mortality are associated with depression. Morbidity^[4] is a result of the functional^[5] impairment that a person experiences in areas of work, school, and relationships. Mortality^[6] is due to death by suicide or accidental death because of the functional impairments (e.g., car accident, illicit drug use, poor nutrition, and neglect of health).

Most people who are depressed respond to treatment, and thus it is unwarranted for anyone to suffer through an episode. The affected person may believe that no one else suffers in the same way and that he or she is alone in having depression. However, depression is a common illness around the world. The lifetime prevalence^[7] for depression is approximately 15%, and in any given 1-year period 18.8 million adults in the United States suffer from depression. Close to 25% of persons seeking medical treatment in their primary care doctor's office suffer from depression. Not only does depression have a personal cost on individuals and their families, it has a significant cost on society. Because many people who are depressed do not seek treatment, the cost of untreated depression to society runs into tens of billions of dollars, in part because of decreased productivity at work and overuse of primary healthcare services. Only approximately half of people with major depression ever receive specific treatment, because symptoms of depression may be inappropriately dismissed as understandable reactions to stress, evidence of personal weakness, or an attempt to receive secondary gain (such as attention from others or disability payments).

What causes depression?

Anthony's comment:

Although depression is not 100% heritable, I believe it often runs in families even if one is not aware of it being present in other family members. In the early 1970s, due to severe anxiety over my identity, I went to see a psychiatrist and received treatment with medication. I needed something that allowed me to function. I was the only one in my extended family, however, who ever sought professional help to deal with anxiety and depression. As a result I was labeled with everything under the sun. But, although no one else has actually been diagnosed with depression in my family, it is my impression that there are in fact family members who deal with depression and anxiety, but due to unawareness, stigma, etc. have not been formally diagnosed or treated.

The causes of depression are not easily defined. When speaking of cause, it is typical to think in terms of infections of the lungs causing pneumonia or of cigarette smoking causing lung cancer. In actuality, most medical conditions cannot be so easily defined as having clearly linked causes. In fact, it took many years of statistical analysis before scientists could demonstrate a clear causal link between cigarette smoking and lung cancer. Even today, people argue, "My grandmother smoked her entire life and died at the ripe old age of 90 from natural causes. How can cigarettes possibly cause cancer?" The reality is that cigarette smoking is only one portion, albeit a big one, of the causal puzzle, which when pieced together leads to lung cancer. This is true of most diseases today. Instead, when physicians talk about cause, they are really talking about risk factors that influence the odds of developing a particular illness. Depression, a complex illness, is more like an illness with multiple causes that influence the odds of someone developing it. Depression runs in families but is not 100% heritable. Depression may occur in someone with no family history for the illness. When considering the causes of depression, the odds are impacted by a variety of sources inside and outside of a person. This variety constitutes what is called the biopsychosocial model^[8] that is typically used. In this model consideration is given to biologic, psychological, and social factors that may contribute to the onset of depression. This model influences most diseases of lifestyle. Look at, for instance, heart disease. Applying the biopsychosocial model to heart disease demonstrates biologic risk factors of family history, the presence of high blood pressure and high cholesterol, and atherosclerosis; psychological risk factors of type A personality and/or an inability to handle stressful events; and social risk factors of smoking, diet, and activity level.

Biologically, depression is associated with changes in various neurotransmitter levels and activity, commonly referred to as a chemical imbalance^[9] in the brain. Additionally, depression frequently runs in families, suggesting a genetic, or heritable, aspect to the illness. Medical conditions and sometimes the medications used to treat those conditions can also cause depressive symptoms. Psychologically, certain personality types are more prone to developing depression. People who have low self-esteem and a pessimistic outlook are at higher risk for depression. Other psychological disorders, such as anxiety, psychosis, or substance abuse disorders, increase the odds of developing depression. Socially, depression is linked to stressful life events, usually entailing loss, such as of a spouse, child, job, or financial security. Depression, however, can also be linked to events generally considered to be uplifting rather than stressful, although from the body's reaction

Depression, a complex illness, is more like an illness with multiple causes that influence the odds of someone developing it.

they are stressful. These events can include marriage, the birth of a child, a job change or promotion, or a move to a new neighborhood or home.

• [1] a medical condition associated with changes in thoughts, moods, and behaviors.
• [2] pertaining to functions and activities of the living matter, such as organs, tissues, or cells.
• [3] environmental influences on the body and mind that can have gradual adverse effects.
• [4] the impact a particular disease process or illness has on one's social, academic, or occupational functioning.
• [5] generally referring to a symptom or condition that has no clearly defined physiologic or anatomic cause.
• [6] death secondary to illness or disease.
• [7] ratio of the frequency of cases in the population in a given time period of a particular event to the number of persons in the population at risk for the event.
• [8] a model used to describe the possible origins of risk factors for the development of various mental illnesses, incorporating the biologic, psychological, and societal factors for a given individual.
• [9] a common vernacular for what is thought to be occurring in the brain in patients suffering from mental illness.