Causes of depression
Knowing about the causes and risk factors for depression can help you understand why depression occurs and how to deal with it.
We know that a range of contributing factors can lead to clinical depression. These include:
- genetics (family history)
- biochemical factors (brain chemistry)
- personality style
- long-term pressures such as abusive relationships, bullying and work stress
- stressful or traumatic events.
We also know that depression can occur during pregnancy and the postnatal period.
Knowing about the causes and risk factors for depression can help you understand why depression occurs and how to deal with it. It's important to know that depression is not a sign of personal weakness, failure, or 'all in the mind'.
Each of us is unique and will respond differently when exposed to environmental, social or psychological triggers.
Sometimes, doctors talk about biological causes – genetics, brain chemistry and personality. Or they might talk about life events, such as the death of a loved one, long term stresses, and abuse.
Depression is often considered to be caused by certain life experiences and personality traits. However, research has shown that the risk of developing depression is partly determined by genetics.
Researchers studying twins have confirmed that depression can be inherited. The findings suggest:
- that about 30% of the predisposition for developing clinical depression is due to genetics
- the remaining 70% is thought to be due to other contributing factors.
Identifying genes that predispose a person to certain types of depression is a growing area of research.
We are currently doing research into exactly what happens in the brain to cause depression.
It's likely that with most instances of clinical depression, neurotransmitter function is disrupted.
What are neurotransmitters?
Neurotransmitters are chemicals that carry signals from one part of the brain to the next. There are many neurotransmitters, serving different purposes. Three important ones that affect a person's mood are serotonin, noradrenaline and dopamine.
In normal brain function, neurotransmitters jump from one nerve cell to the next with the signal being as strong in the second and subsequent cells as it was in the first.
In people who are depressed, the mood regulating neurotransmitters don't function normally. The signal is either depleted or disrupted before passing to the next nerve cell.
In all types of depression, it is likely that the transmission of serotonin is reduced or disrupted.
In people with more severe depression, other neurotransmitter pathways such as those for noradrenaline and dopamine are also likely to be functioning abnormally.
Research has also shown that cells in some parts of the brain can shrink when people are depressed. Ketamine has been shown to powerfully reverse these changes. Ketamine treatment is currently available at the Black Dog Institute through a research trial.
Being sick isn't a pleasant experience. Even short periods of illness can lower our mood.
The effects of chronic pain, being stuck at home or in bed, not being able to do the things we enjoy and the long-term worries about our illness can contribute to depression.
Some medical conditions can also contribute to depression. These include:
- degenerative neurological disorders
- cardiovascular diseases
- brain tumour
- metabolic conditions such as vitamin B12 and folate deficiency
- endocrine disorders (such as thyroid problems, diabetes)
- some cancers (e.g. pancreatic and lung cancer).
Recently, there have been studies looking at whether compromised immune function might play a part in the emergence of depression.
Read more about depression and physical illness.
Personality and temperament can contribute to depression. Certain personality types are more at risk of developing depression than others.
The following personality styles have been associated with a greater risk of depression:
- 'anxious worrying' personality style (highly strung, tense, nervy and prone to stewing over things)
- 'irritable' personality style (easily rattled and with a low tolerance for frustration)
- 'socially avoidant' personality style (shy and avoids social situations due to fear of their limitations, being exposed or of being criticised by other)
- 'personally reserved' personality style (wary of others getting too close and becomes vulnerable and depressed when their inner worlds are exposed to others)
- 'self-critical' personality style (low self-esteem and gives themself a hard time)
- 'rejection sensitive’ personality style (hypersensitive to the quality of interpersonal relationships and perceives others as rejecting or demeaning them).
Remember: just because you have one of these personality styles, it doesn't necessarily mean you will develop depression. Personality style is just one contributing factor.
As we age, our brain function reduces and certain important neurotransmitter pathways that influence our mood can be affected. These age-related changes may be in relation to:
- dementia (some elderly people experience severe depression for the first time after developing dementia)
- high blood pressure or mini-strokes (often unnoticed by the individual and their family).
Sometimes changes to how our brain functions merely reflect an ageing process, particularly in people who are vulnerable to this kind of 'wear and tear'.
Download our depression in older people fact sheet for more information.
- dementia (some elderly people experience severe depression for the first time after developing dementia)
Stress is a part of all our lives
Nearly every one of us can be stressed and depressed by certain life events. Money problems, unemployment, childbirth, divorce, a death in the family and other loss can cause us to feel upset and depressed. These life events and the related stress can 'trigger' a depressive illness in people with a vulnerability to depression.
Past and long-standing stressors (distal stressors) can increase the chance of developing depression.
An uncaring or abusive parent is an example of a past stressor that has been linked to the development of depression. Lack of parental care may result in the child developing low self-esteem and thus being vulnerable to develop depression in adult life.
The death of a parent in childhood does not appear to be a distinct stressor. It may cause depression at the time, but it does not necessarily lead to depression in adulthood in any direct way.
Difficult life events
Most people who develop depression usually describe an important and understandable life event that occurred before the depression started. The events that are most likely to 'trigger' depression are ones where self-esteem is put at risk, compromised or devalued. For most adults, self-esteem is closely linked to an intimate relationship as well as in other important areas, such as a job.
Common triggers of depression related to self-esteem include:
- the break-up of a relationship
- losing your job
- shame due to not living up to your own or others' expectations.
Identifying and understanding the meaning of the life event stressor can be all-important in assisting people to improve their mental health and wellbeing.
Stress contributes to depression through:
- Severity: too much stress can be overwhelming, hard to manage and contributes to feelings of hopelessness. Stress management programs (such as our myCompass program) may be helpful.
- 'Salience' or particular meaning to you: a particular event or set of circumstances is likely to trigger stress in you and may do so repeatedly if re-exposed to those triggers. Counselling or psychotherapy can be helpful in identifying your triggers and why they produce a stress reaction.
- Duration: long-term stress and ongoing issues can cause depression over time.
Examples of ongoing stressors include: worry about a serious illness, difficult or abusive relationships, and caring for elderly or sick family members.
There is no simple or single explanation for why some people develop depression during pregnancy and after the birth of a child. We all respond and cope differently with the stresses associated with labour, childbirth and adjusting to living with a new baby. Short episodes of mood swings often resolve without treatment.
The onset of depression appears to be linked to stress, but stress itself is not the primary risk factor, just the trigger.
Factors associated with an increased risk of postnatal depression include physical illness, previous history of mental illness, adverse childhood experiences with parents, stress, insufficient social supports, pregnancy loss, an unsettled baby, and personality type.
Effects of illness
Pain, discomfort, extreme nausea and vomiting during pregnancy are often associated with depressed mood, as are hormonal imbalances such as those associated with thyroid function.
Mood swings can result as a reaction to caesarean surgery, the anaesthetic used, or as a side effect to medications prescribed to treat illness during pregnancy.
Medical assessment is needed to rule out such causes of depression. For example, following delivery by caesarean section, or where there is a family history of thyroid disease, or if seriously affected by anaemia.
Previous history of mental illness
Women with a previous history of a mental illness are at greater risk of developing depression during pregnancy than women with no prior history of a mental illness.
Depression during pregnancy develops into postnatal depression. Of the women who have depression during pregnancy, 40% will go on to have postnatal depression.
Early parenting experiences
The way we feel we were cared for by our parents when we were children plays a significant role in the way in which we relate to others and form relationships as adults. These early bonding experiences affect our attitudes about ourselves, our relationships and especially our relationships with our children.
Your experience of being parented can impact on your:
- optimism about life
- social relationships
- coping skills and emotional resilience in adulthood
- adjustment to the role of being a parent (experiences of being unwanted or unloved, subjected to criticism, hostility or rejection, experiencing overly-protective parenting, or the absence of a parent in childhood can influence subsequent adjustment).
The task of parenting can be perceived as more stressful and more complex for women who have inadequate role models than for those who have strong role models.
There is evidence to show that growing up in an abusive or uncaring family, or exposure to physical, sexual, or emotional abuse can lead to low self-esteem, patterns of social avoidance, and vulnerability to depression in later life.
These experiences can lead to heightened distress or feelings of increased vulnerability in the face of subsequent stressful life events.
Childbirth itself can trigger memories of past events that involved pain or distress including physical or sexual abuse.
Insufficient family or social support
Practical help, social and emotional support assists a new mother with the adjustments required after the birth of a baby. Support allows her to get the necessary rest and time to spend with her new baby.
After a miscarriage, stillbirth, or termination of a pregnancy, there's a period of grieving for the loss. This can sometimes become more prolonged and result in clinical depression.
Heightened levels of discomfort, pain, stress and anxiety during labour and childbirth are normal. Especially the first time a woman gives birth.
However, childbirth-related stress levels can be heightened after:
- delivery of a very pre-term or sick baby
- an emergency delivery
- a long and painful labour and birth perhaps including instruments to aid in the delivery
- birth of a baby that is slow to breathe or has an abnormal appearance.
It is the way the mother experiences the labour and birth that determines whether it is stressful for her, rather than the way a partner or doctor perceives the process.
A baby that is restless, difficult to settle, or unwell can be stressful to a new mother and to the rest of the family.
Increased levels of fatigue lead to disrupted family routines and lower levels of emotional resilience for parents.
It is important to seek advice from your doctor, or child and family health nurse if you are concerned about your baby's sleeping and feeding routines or any other health matter.
Some personality types appear to be associated with an increased risk of developing depression during pregnancy and after childbirth.
These personality types, include:
- anxious worrier (a mother with this personality style is difficult to reassure and often exhibits pessimistic thoughts)
- socially avoidant (a mother with this personality style lacks self-confidence, doesn't mix much socially, tends to stay at home and often spends a lot of time alone with the baby)
- perfectionist (a mother with this personality style may find the lack of clear patterns and routines associated with parenting quite challenging and stressful)
- self-critical (a mother with this personality style may have low self-esteem and often feel unworthy in comparison to other mothers).