Theories About Causes
Medical research has contributed much to our understanding of depression. However, scientists do not know the exact mechanism that triggers depressive illness. Probably no single cause gives rise to the illness, and researchers continue to piece the puzzle together.
In the past, doctors believed that depression was the result of thoughts or emotions that were troubling for a person. More recently, experts realize that there can be several factors working together that will lead a person to become depressed. The three most important of these are biological, genetic, and environmental factors.
Biological causes are due to changes in the chemistry of the brain, such as fluctuations in the levels of important hormones. Genetic causes are the result of what you inherit from your parents. If one or both of your parents have a vulnerability to depression, then it can be transmitted to you. Environmental factors (also called emotional factors) result from stressful emotional situations, such as a lack of loving parents or the death of a parent during childhood. To make it even more complicated, depression can also occur as a result of a combination of the three factors just mentioned. If you inherited a vulnerability to depression from one of your parents, your brain may react to a stressful event in a way that causes you to get depressed.
Depression can also develop due to a physical illness, a reaction to a medication that you are taking, or as an outcome of substance abuse. In these cases, when the cause is successfully treated, the depression will end.
Genetic Factors
Scientists believe genetic factors play a role in some depressions. Researchers are hopeful, for instance, that they are closing in on genetic markers for susceptibility to manic-depressive disorder.
Recent genetic research also supports earlier studies reporting family links in depression. For example, if one identical twin suffers from depression or manic-depressive disorder, the other twin has a 70 percent chance of also having the illness. Other studies that looked at the rate of depression among adopted children supported this finding. Depressive illnesses among adoptive family members had little effect on a child's risk of depression; however, the disorder was three times more common among adopted children whose biological relatives suffered depression.
Biological Causes
Additional research data indicate that people suffering from depression have imbalances of neurotransmitters, natural substances that allow brain cells to communicate with one another. Two transmitters implicated in depression are serotonin and norepinephrine. Scientists think a deficiency in serotonin may cause the sleep problems, irritability, and anxiety associated with depression. Likewise, a decreased amount of norepinephrine, which regulates alertness and arousal, may contribute to the fatigue and depressed mood of the illness.
Other body chemicals also may be altered in depressed people. Among them is cortisol, a hormone that the body produces in response to stress, anger, or fear. In normal people the level of cortisol in the bloodstream peaks in the morning, then decreases as the day progresses. In depressed people, however, cortisol peaks earlier in the morning and does not level off or decrease in the afternoon or evening.
Researchers don't know if these imbalances cause the disease or if the illness gives rise to the imbalances. They do know that cortisol levels will increase in anyone who must live with long-term stress.
Environmental Situations
Certain environmental situations, such as stress or breakup of important attachments, also may precipitate depression, especially in vulnerable persons.
Research continues to better understand the interaction of genes and environment, and precisely what is inherited.
next: Changes in Brain Chemistry and Other Factors That Contribute to Depression
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