Almost all of us feel low sometimes, usually because of a disturbing or difficult event in our lives. But ongoing sadness or despair can be caused by depression, a serious condition that warrants treatment.
Depression affects 20% of all women, 10% of all men, and 5% or more of all adolescents worldwide. It is ranked as the fourth greatest cause of global illness burden by the World Health Organization and is the second most common psychiatric problem in the U.S. (after anxiety disorders), afflicting about 17.6 million people each year at a cost in the range of about $50 billion a year.
Depression can strike at any age, including in childhood. Studies in the U.S. show that in 2008, between 7.4% and 8.7% of adults (18-49) and 8.3% of adolescents (12-17) had a major depressive episode during the previous year. However, most people first experience depression when they are in their early thirties, and depression is particularly rife among older adults. Depression is not simply a normal reaction to the challenges of growing older, such as the death of a spouse or friends and the physical limitations of age, but is a medical condition without a known cause.
Depressive reaction. A less-severe and often temporary depression that arises from a specific life situation. In modern diagnostic language, a depressive reaction to a specific life stress is technically called a "stress response syndrome" (formerly known as an "adjustment disorder with depressed mood"). The symptoms can be severe, but unless they involve additional symptoms such as changes in sleep and appetite or thoughts of suicide, they usually do not need medication treatment and will abate over time -- anywhere from two weeks to six months. Psychotherapy is sometimes recommended if symptoms start to interfere with normal everyday functioning.
Major depression. A serious condition that can lead to an inability to function or suicide. Sufferers experience not only a depressed mood, but also have difficulty performing simple daily tasks, lose interest in their usual activities, extreme fatigue, sleep problems, or feelings of guilt and helplessness. They can sometimes also lose touch with reality, having delusions (such as believing they have committed a sin, or are dying) or hallucinations (such as hearing an imaginary voice telling them they are no good), in severe cases. It can be a cyclical illness, so while most patients recover from their first depressive episode, the recurrence rate is high -- perhaps as high as 60% within two years and 75% within 10 years. After 15 years, 90% of individuals will have suffered a recurrence or relapse of depression.