Depression is a chronic mental disorder that affects all areas of an individual’s life. It is characterized by extreme despair, feelings of worthlessness, persistent fatigue and/or thoughts of suicide. Approximately 10 percent of adults over the age of 18 suffer from depression in the United States each year, according to the website Healthy Place. While the exact cause of depression is unknown, it has been suggested that a combination of biological factors and environmental stressors contribute to the onset and progression of the disorder.

Genetics

Genetics play an important part in the development of depression. Depression tends to run in families, suggesting that it is largely hereditary. An individual is 1.5 to three times more likely to develop the condition if she has a close relative with depression than someone who does not have a family link to it, according to the website All About Depression. While depression may be generational for most families, it is possible to develop the disorder even if there is no family history of it.

Abnormal Brain Structure and Chemistry

Abnormal brain structure and chemistry contribute to the development of depression. The National Institute for Mental Health states that the brain structure of people with depression seems to vary slightly from people who do not have the disorder. When a person has depression, the parts of their brain responsible for regulating mood, thinking, sleep, appetite and behavior do not function normally. People who suffer from depression have an imbalance in neurotransmitters, chemicals that brain cells use to communicate, which prevents the brain from functioning effectively.

Hormone Imbalances

There appears to be a link between depression and hormone imbalances. Depressed people appear to have an excess amount of cortisol, a hormone that regulates the body’s response to stress, anger and fear, according to Psych Central. A healthy person’s cortisol level peaks in the morning, then gradually decreases throughout the day, while a depressed person’s cortisol level peaks in the morning, but remains elevated throughout the day and night, resulting in a hormone imbalance.

In addition, certain medical conditions can affect a person’s hormonal balance and, therefore, trigger depression. Hypothyroidism, a condition in which the thyroid gland does not produce enough hormones, is also known to cause depression in some people.