depression

In medicine, an emotional state characterized by sadness, unhappy thoughts, apathy, and dejection. Sadness is a normal response to major losses such as bereavement or unemployment. After childbirth, postnatal depression is common. Clinical depression, which is prolonged or unduly severe, often requires treatment, such as antidepressant medication, cognitive therapy, or, in very rare cases, electroconvulsive therapy (ECT), in which an electrical current is passed through the brain.

Periods of depression may alternate with periods of high optimism, over-enthusiasm, and confidence. This is the manic phase in a disorder known as manic depression or bipolar disorder. A manic depressive state is one in which a person switches repeatedly from one extreme to the other. Each mood can last for weeks or months. Typically, the depressive state lasts longer than the manic phase.

Depression costs the USA around $12.4 billion each year in treatment. Another $23.8 billion is paid for by employers, arising from absenteeism and lost productivity. The National Institute of Mental Health estimated in 1998 that 17–20 million adults have a clinical depression each year and that depression will affect one in every five women and one in every ten men during their lifetimes.

Since 1990, the USA has held an annual National Depression Screening Day with free screening tests for depression and post-traumatic stress disorder (PTSD) given at some 1,750 sites around the nation and by 1,400 other doctors. The event had an added significance in 2001, coming exactly one month after the 11 September terrorist attacks on the USA. Symptoms have to continue for a full month to qualify for a diagnosis of PTSD.

In 1996, US researchers identified a connection between depression in women and low bone density, leading to an increased risk of fractures in later life. This is possible due to the increased levels of the steroid hydrocortisone during depressive periods.

depression

In economics, a period of low output and investment, with high unemployment. Specifically, the term describes two periods of crisis in world economy: 1873–96 and 1929 to the mid-1930s (see Great Depression).

depression

The isobars around a low-pressure area or depression. In the northern hemisphere, winds blow anticlockwise around lows, approximately parallel to the isobars, and clockwise around highs. In the southern hemisphere, the winds blow in the opposite directions.

In meteorology, a region of relatively low atmospheric pressure. In mid-latitudes a depression forms as warm, moist air from the tropics mixes with cold, dry polar air, producing warm and cold boundaries (fronts) and unstable weather – low cloud and drizzle, showers, or fierce storms. The warm air, being less dense, rises above the cold air to produce the area of low pressure on the ground. Air spirals in towards the centre of the depression in an anticlockwise direction in the northern hemisphere, clockwise in the southern hemisphere, generating winds up to gale force. Depressions tend to travel eastwards and can remain active for several days.

A deep depression is one in which the pressure at the centre is very much lower than that around it so that it produces very strong winds, as opposed to a shallow depression in which the winds are comparatively light. A severe depression in the tropics is called a hurricane, tropical cyclone, or typhoon, and is a great danger to shipping; a tornado is a very intense, rapidly swirling depression, with a diameter of only a few hundred feet or so.