Major depression also seems to run in families, but it can also develop in people who have no family history of depression. Either way major depressive disorder is often associated with changes in brain structures or brain function.
People who have low self-esteem, who are consistently pessimistic, or who are readily overwhelmed by stress, are also prone to depression. Physical changes in the body can also trigger mental health problems such as depression. Research demonstrates that stroke, heart attack, cancer, Parkinson's disease, and hormonal disorders can cause depression.
The depression can contribute to the person's medical problem, as then can become apathetic and unwilling to care for their physical needs. A severe stressor such as a serious loss, difficult relationship, or financial problem can also trigger a depressive episode. A combination of genetic, psychological, and environmental factors is often involved in the onset of depression.
There are a number of causes and factors that may increase the chance of depression, including, but not limited, to the following:
- Death or a loss. Trauma prevents certain parts of the brain (hippocampus and frontal lobe, where decisions are made) from developing properly. Sadness or grief from the death or loss of a loved one, though natural, can also increase the risk of depression.
- 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.
- Biological differences. People with depression appear to have physical changes in their brains. The significance of these changes is still uncertain, but may eventually help pinpoint causes. Also, neurotransmitters (naturally occurring brain chemicals linked to mood) are thought to play a direct role in depression.
- High stress hormone levels. Certain neurochemicals are also involved, such as a surplus of noradrenaline, perhaps as a result of the structural problem. Changes in the body's balance of hormones may be involved in causing or triggering depression. Hormone changes can result from thyroid problems, menopause or a number of other conditions. Recent studies indicate that serotonin, which is targeted by most antidepressants (SSRIs), is not as much a factor in depression as the long-term presence of stress hormone cortisol.
- 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. Although there may be a genetic basis to some depression, it must be triggered by some traumatic or stressful event.
- Certain medications. For example, some drugs used to treat high blood pressure, such as beta-blockers or reserpine, can increase your risk of depression.
- Low self-esteem. 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.
- Conflict. Depression may result from personal conflicts or disputes with family members or friends.
- Abuse. Past physical, sexual, or emotional abuse can cause depression later in life.
- 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.
- Serious illnesses. Sometimes depression co-exists with a major illness or is a reaction to the illness.
Physiological problems, plus learned beliefs and behaviors, make functional decisions difficult, and the results reinforce the depression in a vicious cycle.