Causes of Depression

This resource booklet has been localised for the Hong Kong context and translated to Traditional Chinese by Coolminds, a mental health initiative run by Mind HK and KELY Support Group. For more information on Coolminds, please visit www.coolmindshk.com

Thank you to the Black Dog Institute for donating their resources and for allowing us to adapt this. For the original version of this resource, please refer to the Black Dog Institute’s website: www.blackdoginstitute.org.au

What this fact sheet covers:

Factors involved in developing depression
Key points to remember
Where to get more information

Introduction

Unlike other illnesses or disorders, there is no simple explanation as to what causes depression.

In general, depression can be due to a number of factors including stresses which can range from mild to severe, combined with vulnerability or predisposition to depression that can result from biological, genetic or psychological factors.

Each type of depression is associated with different mixtures of causes. For psychotic or melancholic depression, physical and biological factors are relevant. In contrast, for non-melancholic depression, the role of personality and stressful life events are important.

Genetic factors

There is strong evidence that genetic factors play a significant role in a person’s predisposition towards developing depression, especially melancholic depression, psychotic depression and bipolar disorder. No single gene is likely to be responsible, but rather a combination of genes.

The predisposition to develop depression can be inherited. The genetic risk of developing clinical depression is about 40% if a biological parent has been diagnosed with the illness, with the remaining 60% being due to factors within the individual’s own environment. Depression is unlikely to occur without stressful life events, but the risk of developing depression as a result of such an event is strongly genetically determined.

Biochemical Factors

Our knowledge of the human brain is still fairly limited, therefore we do not really know what actually happens in the brain to cause depression. It is likely that with most instances of clinical depression, neurotransmitter function is disrupted. Neurotransmitters are chemicals that carry signals from one part of the brain to the next. There are many neurotransmitters serving different purposes. However, three important ones that affect a person’s mood are serotonin, noradrenaline and dopamine.

In normal brain function, neurotransmitters interact with a series of nerve cells, with the signal being as strong in the second and subsequent cells as it was in the first. However, in people who are depressed, mood regulating neurotransmitters fail to function normally, so that the signal is either depleted or disrupted before passing to the next nerve cell.

Physical Illness

In a simple sense, physical illness can lead to depression through the lowered mood that we can all experience when we are unwell, in pain or discomfort, confined and less able to do the things we enjoy.

Illness can also change the body’s functioning in a way that leads to depression. Even if the illness isn’t making us feel down we can still suffer from depression. For example:

It is known that certain cancers can produce a depressive illness – in these cases a person might be quite unaware that they are suffering from depression.
Compromised immune functioning might play a part in the emergence of depression, although further research is needed to establish this link.

The ageing brain

As we age, our brain’s general functioning can become compromised and this can affect the neurotransmitter pathways which influence mood state. Three reasons for these changes are worth mentioning in relation to depression:

Late onset depression: Elderly people who develop dementia may also develop a severe depression for the first time; this type of depression is commonly of a psychotic or melancholic type and reflects the disruption of circuits linking certain basal ganglia and frontal regions of the brain.
These brain changes can reflect an ageing process, particularly in people who are vulnerable to this kind of ‘wear and tear’.
In others however, high blood pressure or mini-strokes (often unnoticed by the individual and their family) may contribute. Good blood pressure control can reduce the chance of depression in some people.

Gender

Gender is a partial but incomplete explanation of why people may develop depression. Equal numbers of men and women develop melancholic depression. However, studies have shown that there is a much greater likelihood of women developing non-melancholic depression than men. Some of the explanations for this are:

Women are more likely than men to ‘internalise’ stress, thereby putting them at greater risk of developing depression.
Women with unsatisfactory marriages or who are caring for a number of young children are also highly over represented among samples of depressed people.
Hormonal factors commencing in puberty may account for the increased chance in women of developing anxiety (a precursor to depression) or depression.

Stress

It is important to recognise that nearly every individual can be stressed and depressed by certain events. Most people get over the stress or depression within days or weeks while others do not. Ways that stress can lead to depression include the following:

Past or long-standing stresses can increase the chances of an individual developing depression in later years e.g. growing up in an abusive or uncaring family may increase the risk of developing depression in adult life.
Events that affect a person’s self-esteem such as the break-up of a close relationship or marriage
Feelings of ‘shame’ for example, thinking they have not lived up to their own or others’ expectations.

Personality

Our research has shown that people with the following personality types are more at risk of developing depression than others. Those who are high on the first four factors are at distinctly greater risk to depression (especially non-melancholic depression):

High levels of anxiety, which can be experienced as an internalised ‘anxious worrying’ style or as a more externalised ‘irritability’.
Shyness expressed as ‘social avoidance’ and/or ‘personal reserve’.
Self-criticism or low self-worth.
High interpersonal sensitivity.
Perfectionism is somewhat protective against the onset of depression but if depression occurs, it can result in longer episodes.
A ‘self-focused’ style is likely to be at greater risk for brief depressive episodes only

Key points to remember

There is no single cause for depression; rather it’s a combination of stress and a person’s vulnerability to developing depression.
The predisposition to developing depression can be inherited.
Other biological causes for depression can include physical illness, the process of ageing and gender.
Stress can trigger depression but understanding its particular meaning to the person is important.
Certain temperament and personality styles pose risks for developing non-melancholic depression.