Traumatic events, such as a sudden loss of a loved one, abuse, or even natural events such as earthquakes, can cause severe immediate or delayed depression, from which recovery takes a long time. Most people are able to cope with the emotional pain and eventually move beyond it without becoming chronically depressed. People who do develop acute or chronic depression after loss may have predisposing factors, including genetic or biologic ones, that make them more vulnerable. The existence or absence of a strong social network of family, friends, or both also has a major positive or negative effect, respectively, on recovery. Biologic Factors Neurotransmitters .
Neurologic factors appear to play a primary role in major depressive episodes.
The degree to which these chemical messengers are disturbed may be determined by other factors such as light or genetic susceptibility. For example, researchers have identified a defect in the gene known as SERT, which regulates serotonin, that has been linked to depression . These forms of depression recede or stop after menopause. Researchers are looking at certain steroid hormones in the brain that regulate progesterone and the activity in areas of the brain that control reproductive hormones. Low levels of these steroids may play a role in depression.