Causes of depression are complex and not entirely identified. Depression usually develops as a result of several interacting factors. The extent to which genetic and environmental influences play a role varies from person to person and cannot always be clearly determined in individual cases.
A genetic predisposition, neurobiological disturbances, and certain developmental and personality-related (psychosocial) factors form the basis of most explanatory models of depression.
Those affected often have a lower tolerance for emotional, physical, and biographical stress than healthy individuals. This particular vulnerability plays a significant role in both the onset and persistence of depression.
Depressive episodes are often triggered by personally distressing events or situations of excessive demand. People at risk tend to react more sensitively to such stressors than others.
Genetic Influences on Depression
A large body of evidence from family and twin studies points to genetic contributions for causing depression. The twin studies compare disease frequencies in identical twins. Only half of the identical twins get ill if the sibling develops depression. It means that other factors than genetics contribute to the onset of depression in the second half.
The family history puts their offspring at an increased risk of depression. As a result, a child with one depressed parent is 10–15% more likely to develop depression than the average. Children are 20–40% more likely to be at risk if both parents experience depression. Such results prove the multi-factorial genesis of depression.
The exploration of numerous genes and their influence on depression didn’t show one particular gene causing the illness. This means that an interaction of several genes is necessary to trigger the onset of depression. So even the genetic component of depression requires the coordinated action of various genes.
Metabolic and Functional Disturbances in the Brain and Depression
Many studies suggest that depression is associated with characteristic changes in brain chemistry. Certain messenger substances, known as neurotransmitters—such as serotonin, dopamine, noradrenaline, acetylcholine, and gamma-aminobutyric acid (GABA)—appear to be out of balance. Compared to healthy individuals, people with depression often show reduced activity of serotonin, noradrenaline, or dopamine.
In addition, imaging studies have shown altered activity in the so-called limbic system during a depressive episode. The limbic system, which plays a key role in regulating stress and processing emotions, is partly responsible for how feelings are experienced and managed. Changes in this system may help explain the increased emotional vulnerability seen in people with depression and why significant life events often precede the onset of the illness.
Another contributing factor to the development of depression may lie in early childhood experiences. An overly anxious or overprotective parenting style, the development of “learned helplessness,” and limited coping skills in dealing with stress can increase the risk of depression. These factors may be both causes and consequences of the illness. For example, overprotective behavior by parents may reflect an early awareness of a child’s emotional vulnerability.
The early loss of a parent, disturbances in the mother–child relationship, or low self-esteem from an early age can also lead to heightened sensitivity to disappointment. Unprocessed experiences of loss or trauma—such as sexual abuse or exposure to disasters—may increase the likelihood of depression later in life, particularly during new crises, such as the end of a relationship. Individuals described as having a “melancholic” personality type are also considered at higher risk. This includes people who tend to be self-doubting, overly conscientious, orderly, highly performance-oriented, and self-sacrificing.
The socioeconomic status and the severity of depression are negatively related. The scientists claim that a fourfold increased risk of depression is the attribute of sexually or physically abused women in childhood compared with women without such experiences.
Reactive Factors Causing Depression
In many cases, depression develops after critical or stressful life events. These may include the loss of a partner or family member, conflicts in close relationships, separation or divorce, or significant changes in daily life, such as retirement. It has been shown that stressful life events can trigger neurobiological reactions, including increased release of the stress hormone cortisol, which is often found at elevated levels in people with depression.
Physical illnesses—such as chronic pain, cancer, cardiovascular disease, or dementia—and certain medications may also contribute to the onset of depression.
Environmental Effects Triggering Depression
Converging evidence indicates that environmental exposures can contribute to the onset of depression. Air pollution, use of herbicides, food preservatives and other chemicals in every area of urban life can affect the activity of certain brain cells (i.e. serotonergic and dopaminergic neurons.)
Cultural Background and Depression
The cultural factors may influence symptoms of depression. For instance, in some cultural contexts, mental distress is primarily expressed through physical symptoms. This can sometimes make it challenging for doctors and psychologists to identify depression. Therefore, while diagnosing depression, it’s essential to consider culture-specific factors and its nuances.
Additional Possible Risk Factors for Depression
Research suggests that, in addition to the mechanisms described above, the following factors may increase the risk of developing depression: being female, living alone, residing in large cities, having limited social contacts, lower levels of education, unemployment, cannabis use, and alcohol misuse.
Frequency, Ethnic and Gender Differences in Depression
- Depression occurs in people of all cultures, all social classes, and nationalities
- Race or ethnic origin has no influence on the development of depression.
- While approximately 25% of adult women develop depression, only about 10% of all men are affected.
- Worldwide, the percentage of people developing depression varies between 8% and 20%.
- The average age of manifestation of a depressive disorder lies between the ages of 20 and 40.
Causes of Depression. Summary
There is a scientific consensus that depression originates from a combination of biological, genetic, psychological, and social factors.
There are internal and external factors causing depression. The internal factors are the genetic predisposition and changes in certain brain areas. They respond well to the treatment with medication. The external factors are environmental influences and changing life circumstances.
Read More About Depression
- Treatment for Depression
- Symptoms of Depression
- Diagnosis of Depression
- Types of Depression
- Relapse Prevention of Depression
- Depression caused by Physical Illnesses
- Self-Assessment Test for Depression
- Postpartum Depression
- Dysthymia
- Catatonic Depression
- Premenstrual Dysphoric Disorder (PMDD)
- Relaxation Techniques in Therapy for Depression
- Helping Family Members with Depression
- Psychotherapy for Older Adults with Depression
- Misdiagnosing Depression
- From Early Understanding to Modern Diagnosis of Depression
- Antidepressants. What They Are
- Feeling Depressed? Effects of Loneliness and Social Isolation
