Some types of depression run in families, indicating that a biological vulnerability to depression can be inherited. This seems to be the case especially with bipolar disorder. Studies have been done of families in which members of each generation develop bipolar disorder. The investigators found that those with the illness have a somewhat different genetic makeup than those who do not become ill. However, the reverse is not true. That is, not everybody with the genetic makeup that causes vulnerability to bipolar disorder will develop the illness. Apparently, additional factors, possibly a stressful environment, are involved in its onset and protective factors are involved in its prevention.
Major depression also seems to occur in generation after generation in some families, although not as strongly as in bipolar I or II. Indeed, major depression can also occur in people who have no family history of depression.
An external event often seems to initiate an episode of depression. Thus, a serious loss, chronic illness, difficult relationship, financial problem, or any unwelcome change in life patterns can trigger a depressive episode. Very often, a combination of genetic, psychological, and environmental factors is involved in the onset of a depressive disorder.
Nothing in the universe is as complex and fascinating as the human brain. The over 100 chemicals that circulate in the brain are known as neurochemicals or neurotransmitters. Much of our research and knowledge, however, has focused on four of these neurochemical systems: norepinephrine, serotonin, dopamine, and acetylcholine. In the new millennium, after new discoveries are made, it is possible that these four neurochemicals will be viewed as the "black bile, yellow bile, phlegm, and blood" of the 20th century.
Different neuropsychiatric illnesses seem to be associated with an overabundance or a lack of some of these neurochemicals in certain parts of the brain. For example, a lack of dopamine at the base of the brain causes Parkinson's disease. Alzheimer dementia seems to be related to lower acetylcholine levels in the brain. The addictive disorders are under the influence of the neurochemical dopamine. That is to say, drugs and alcohol work by releasing dopamine in the brain. The dopamine causes euphoria, which is a pleasant sensation. Repeated use of drugs or alcohol, however, desensitizes the dopamine system, which means that the system gets used to the drugs and alcohol. Therefore, a person needs more drugs or alcohol to achieve the same high feeling. Thus, the addicted person takes more substance but feels less and less high.
The different types of schizophrenia are associated with an imbalance of dopamine (too much) and serotonin (poorly regulated) in certain areas of the brain. Finally, the depressive disorders appear to be associated with altered brain serotonin and norepinephrine systems. Both of these neurochemicals may be lower in depressed people. Please note that abnormalities of these neurochemicals are "associated with" instead of "caused by," because we really don't know whether low levels of neurochemicals in the brain cause depression or whether depression causes low levels of neurochemicals in the brain.
What we do know is certain medications that alter the levels of norepinephrine or serotonin can alleviate the symptoms of depression. Some medicines that affect both of these neurochemical systems appear to perform even better or faster. Other medications that treat depression primarily affect the other neurochemical systems. The most powerful treatment for depression, electroconvulsive therapy (ECT), is certainly not specific to any particular neurotransmitter system. Rather, ECT, by causing a seizure, produces a generalized brain activity that probably releases massive amounts of all of the neurochemicals.
Women are twice as likely to become depressed as men. However, scientists do not know the reason for this difference. Psychological factors also contribute to a person's vulnerability to depression. Thus, persistent deprivation in infancy, physical or sexual abuse, clusters of certain personality traits, and inadequate ways of coping (maladaptive coping mechanisms) all can increase the frequency and severity of depressive disorders, with or without inherited vulnerability.
The effect of maternal-fetal stress on depression is currently an exciting area of research. It seems that maternal stress during pregnancy can increase the chance that the child will be prone to depression as an adult, particularly if there is a genetic vulnerability. It is thought that the mother's circulating stress hormones can influence the development of the fetus' brain during pregnancy. This altered fetal brain development occurs in ways that predispose the child to the risk of depression as an adult. Further research is still necessary to clarify how this happens. Again, this situation shows the complex interaction between genetic vulnerability and environmental stress, in this case, the stress of the mother on the fetus.
What are the main factors that cause depression?
There are a number of factors that may increase the chance of depression, including the following:
- Abuse. Past physical, sexual, or emotional abuse can cause depression later in life.
- Certain medications. For example, some drugs used to treat high blood pressure, such as beta-blockers or reserpine, can increase your risk of depression.
- Brain Chemistry Imbalance. Depression is believed to be caused by an imbalance in the neurotransmitters which are involved in mood regulation. Neurotransmitters are chemical substances which help different areas of the brain communicate with each other. When certain neurotransmitters are in short supply, this may lead to the symptoms we recognize as clinical depression.
- Female Sex Hormones. It has been widely documented that women suffer from major depression about twice as often as men. Because the incidence of depressive disorders peaks during women's reproductive years, it is believed that hormonal risk factors may be to blame. Women are especially prone to depressive disorders during times when their hormones are in flux, such as around the time of their menstrual period, childbirth and perimenopause. In addition, a woman's depression risk declines after she goes through menopause.
- Conflict. Depression may result from personal conflicts or disputes with family members or friends.
- Death or a loss. Sadness or grief from the death or loss of a loved one, though natural, can also increase the risk of depression.
- Genetics. A family history of depression may increase the risk. It’s thought that depression is passed genetically from one generation to the next. The exact way this happens, though, is not known.
- Major events. Even good events such as starting a new job, graduating, or getting married can lead to depression. So can moving, losing a job or income, getting divorced, or retiring.
- Other personal problems. Problems such as social isolation due to other mental illnesses or being cast out of a family or social group can lead to depression.
- Physical conditions. Serious medical conditions like heart disease, cancer, and HIV can contribute to depression, partly because of the physical weakness and stress they bring on. Depression can make medical conditions worse, since it weakens the immune system and can make pain harder to bear. In some cases, depression can be caused by medications used to treat medical conditions.
- Poor Nutrition. A poor diet can contribute to depression in several ways. A variety of vitamin and mineral deficiencies are known to cause symptoms of depression. Researchers have also found that diets either low in omega-3 fatty acids or with an imbalanced ratio of omega-6 to omega-3 are associated with increased rates of depression. In addition, diets high in sugar have been associated with depression.
- Personality. People who have low self-esteem, who consistently view themselves and the world with pessimism or who are readily overwhelmed by stress, are prone to depression. Whether this represents a psychological predisposition or an early form of the illness is not clear.
- Substance abuse. Nearly 30% of people with substance abuse problems also have major or clinical depression.
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