The major causes of depressive illnesses are complex and not fully understood. Researchers and experts today attribute depression to three major causes, namely biological, genetic and environmental and psychological factors. Among the major causes for depression are biological causes, genetic causes and Environmental and psychological causes
Biological causes
The command structure of the brain is affected by chemicals called neurotransmitters which carry a command or message through the brain’s network of special brain cells called neurons. The limbic system is a part of the brain that regulates emotions, sexual desire, and stress response. The working of the limbic system is so crucial that any problem in the communication network or neurotransmitter activity could affect or alter mood, behavior, and sleep patterns. Among the neurotransmitters identified, scientists have established links between three main transmitters of norepinephrine, serotonin and dopamine. Other neurotransmitters too have a role in depression onset and its development. However scientists have been largely unable to link depression to changing levels of neurotransmitters consistently. Some researchers also speculate on the possibility on neurotransmitter level change to be the cause for depression.
Brain-derived neurotrophic factor (BDNF) is also an important factor that is associated with depression. Reduced expression of BDNF has been determined in depressed people. There is also considerable evidence that this reduced expression is related to suicide too.
Hormones and hormonal irregularities are also attributed as causes for depression. A big percentage of the depressed people have abnormal amounts of certain hormones in their blood, which could account for depressive illness symptoms like sleep and appetite change etc. Also people suffering from certain endocrine disorders could experience depression.
People with depression experience disturbed sleep patterns. Some may wake up several times during the night, while some wake up early in the morning and cannot go back to sleep. There are also others who may sleep for hours, yet never feel rested. Scientists have determined that when depressed people find sleep, their sleep is abnormal. Using EEGs, researchers have determined that sleep cycles of depressed people run backward. People with depressive illness have more eye movements during Rapid Eye Movement (REM) sleep. Changing the sleep patterns is a treatment for depression, which again point out to the association of depression and circadian rhythms.
Genetic causes
Most people with major depression or bipolar disorder have relatives struggling with the illness. Although it was earlier uncertain to know if depression was inherited, researchers today perceive that it could be inherited to some extent. Sometimes the illness may not be inherited, but the tendency to develop one could be inherited. Research on families has showed that brothers, sisters and parents of people with major depression are more likely to develop this illness, than others. Bipolar depression is particularly evident running across families.
It has been determined that about 50% of all people with bipolar disorder have a parent with a history of the illness. The influence of heredity has also been proved with twin studies. In 1987 scientists had claimed to have identified the gene liked to depressive illness as being found on chromosome 11, based on studies with the Amish people in Pennsylvania. However these findings were later rejected when the results were found to be inconsistent, with an enlarged group. Researchers from the US and Belgium had later concluded that a gene on X chromosome make people vulnerable to bipolar depression. Many other researchers have attributed other chromosomes too, to the illness.
Scientists have now claimed to have identified certain variations in some people’s genes, which they suggest as causing depression. A British team investigating genetic affects has found a DNA region linked to depression. This has been replicated by another team from the US. Both studies have been published in the American Journal of Psychiatry, with both teams attributing the strong link of depression to genetic variation in chromosome 3p 25-26. These findings are very significant as replicative findings in genetics are very rare. However as the linking of genetics and depression is too complex, progress on identification of these genes is slow, but is a growing area of research.
Environmental and psychological causes
Much before biological and genetic aspects for depression susceptibility were understood, physicians knew that the external environment and events could affect the mind. Psychological and environmental factors cause anxiety and depression, which are influenced by genetic predisposition. But it is not yet clear as to how they affect the brain functioning to result in depressive symptoms. For example with regard to environment, light is immensely associated with depression.
Lighting conditions affect the mood of the people to a large extent, which are likely to affect work behavior and work performance, although this cannot be uniformly applied to all. Light radiations stimulate chemical reactions in the blood and other tissues when absorbed directly by the skin. It is important to note that the biological lighting needs of people are different from visual lighting needs, particularly for staff working during nights. Exposure to light helps in reducing depression, alleviating pain and improving sleep. Facility lighting need to provide high quality lighted environment while fulfilling human needs for light.
The relationship between stress, the body’s response, and depressive illnesses is very complex. Most researchers agree that some people could become clinically depressed after a stressful event. Stressful events not only include a negative and traumatic ones like a job loss, death of a close relative etc.; positive events too like getting a job or getting marriage could cause stress. Also for some people, difficulties in life and depression are inter-related. Researchers point out that people who experience stress repeatedly or over a long period of time, learn to feel helpless. This is particularly true when they have no control over the stressful situation. Researchers attribute this learned helplessness to depression.
An unhappy childhood can also lead to depression during adulthood. Childhood difficulties including separation from family, sexual or physical abuse, family turmoil etc. have been more observed in adults with depression than healthy people. Here too the manner in which childhood sufferings lead to depression in adult life is uncertain. Some scientists suggest that unhappy children would find it more difficult to cope with the changes, particularly during adolescence. As they progress towards adulthood, they would find the new roles being too difficult.
