The precise cause of depression is not known, but evidence points to several factors, including:

 
• Heredity  
• Biochemical makeup  
• Psychological makeup  
• Stressful life events  
• Fluctuating hormone levels  
• Other factors such as general medical conditions and certain medications

Heredity

Depression does “run in families.” People with a close relative who has had major depression or bipolar disorder are twice as likely to develop depression themselves.

Biochemical Makeup

Every human being has a unique biochemical makeup. Whether or not a person will experience depression (or other neurological disorders) depends largely on the amount of certain brain chemicals and how they interact in the central nervous system (CNS).

A person’s biochemistry is an intricate balancing act. Think of a choreographed ballet with a troupe of dancers performing at once. If one or more of the dancers are out of step, the whole production is thrown off balance. So it is with an individual’s biochemistry.

The brain is the “master” control center that governs our lives in every conceivable way. Just as messages from the brain (in the form of electrical impulses) control our movements, other messages control our emotions.

 
• Neurons, or nerve cells, are the most basic units in the brain. Neurons are separated by gaps called synapses.  
• Chemical substances called neurotransmitters carry messages or signals across these gaps to various nerve cells.  
• If there is a deficiency or an imbalance in certain neurotransmitters, a variety of disorders can result.  
• The neurotransmitters serotonin, dopamine, and norepinephrine are the chemical messengers believed to be responsible for moods and emotions. Serotonin, in particular, has been implicated in depression. It is believed that a deficiency in the brain of the chemical messenger serotonin - or a disruption in the way it is able to perform its actions as a chemical messenger - has a profound negative effect on mood and emotions.

Psychological Makeup

It is said that a person’s basic personality traits are often defined in early childhood. One defining factor is the social environment to which we are exposed. What happens to us in childhood can have a deep-rooted effect on our attitudes and behaviors in adulthood. For instance:

 
• Long-standing neglect, repression, or abuse in childhood will affect one’s view of the world later on.  
• Conditions of social deprivation, such as overcrowding and the lack of a confiding relationship with a trustworthy person, can affect the quality of one’s relationships throughout life.

Stressful Life Events

A person’s reactions to external factors can affect the normal level and activity of the chemical messengers in the brain, thus affecting mood and emotions. A stressful life event can plunge a person into clinical depression, especially if a person is at risk for depression due to other factors. Stressful life events include:

 
• Prolonged medical illness  
• Illness or death of a loved one  
• Divorce  
• Ending a close relationship  
• Loss of a job  
• Moving to a new home  
• Financial or legal problems

Fluctuating Hormone Levels

In women, fluctuating hormone levels can contribute to depression. Conditions linked to hormones in women are:

 
• Premenstrual syndrome. Approximately 3% to 8% of women in their reproductive years are affected with premenstrual syndrome (PMS) during the week or so before their menstrual period. PMS is characterized by depressed mood, mood swings, irritability, and tension or anxiety. It lessens with the onset of the menstrual period each month.  
• Depression after pregnancy. This temporary form of depression is strongly linked to hormonal fluctuations following pregnancy, but social factors may play a role in some cases. For instance, a professional woman who is suddenly faced with being home every day, essentially alone with a baby, may feel isolated and depressed.  
• Depression in menopause. Menopausal depression was once attributed to middle-aged women feeling sad over the loss of their childbearing capabilities (the loss of their “youth” or “femininity”), and the loss of their grown children (the “empty nest”). There is no evidence that this is true. In fact, evidence suggests that for some women, menopause and the “empty nest” may signify a new freedom in their lives to pursue long-delayed interests and devote more time to their own needs.

However, hormonal fluctuations in menopause are real, and some women suffer from mood swings, fatigue, and depression. Hormone replacement therapy (HRT) can lift mood and fatigue among women who are medically able and who choose to take HRT.

Other Factors

Other factors that can lead to depression include:

 
• Alcohol or drug abuse  
• Use of certain medications, such as steroids and some blood pressure medications  
• Underlying general medical conditions that can cause depressive symptoms, such as hypothyroidism (underactive thyroid gland), chronic fatigue syndrome, and others  
• “Burnout,” a depletion of mental and physical energy usually stemming from prolonged overwork and/or an overload of demands and obligations placed upon an individual