Exactly what causes depression is not known, but
research has revealed several possible causes and contributory factors. These
include both biological/physical and social/psychological factors. There is
often a combination of factors at play in an individual’s history and
environment and different people become depressed for different reasons.
Sometimes a specific trigger may be identified, but
at other times people seem to become depressed for no reason at all. This is
more likely when the person has experienced previous depressive episodes.
- Neurotransmitters: Studies have shown that
brain chemicals (neurotransmitters) play a mediating role in the
development of depression. When the functioning of brain chemicals is
disturbed, depression can occur (e.g. following the use of recreational
drugs such as Ecstasy). Several different neurotransmitter systems may be
involved, but the two that have been more frequently implicated are
serotonin (5-HT) and norepinephrine (NE). Studies have also shown a third
brain chemical, dopamine, to play a role in both depressed and elevated
- Hormonal factors: Increased secretion of
cortisol from the adrenal gland during stress is associated with
depression. Hypercortisolaemia has been shown to damage the hippocampus
(an area of the brain associated with hormonal and behavioural
regulation). Thyroid gland disorders are often associated with mood
disorders. All patients suffering from a MDD should be tested for
hypothyroidism (i.e. underactive thyroid). Studies have shown about 10
percent of patients, especially those with Bipolar Disorder, have
detectable concentrations of anti-thyroid antibodies (produced by the body
in order to fight disease which in this instance turns upon the body
itself). There is also an association between anti-thyroid antibodies and
post-natal depression. Alterations in the pattern of growth hormone
release have also been observed.
considerations: CT Scans and MRI studies, although inconsistent, have
shown differences in the size of some of the brain structures (e.g.
caudate nucleus) in depressed patients as well as alterations in blood
flow to certain areas. Mood disorders involve pathology of the limbic
system (emotional centre, memory function). The basal ganglia (stooped
posture, motor slowness) and the hypothalamus (changes in sleep, appetite
and sexual behaviour) have also been implicated.
- Genetic factors: Inherited factors are an
important component in the development of mood disorders. Having a close
relative who has suffered from a depressive disorder, especially Bipolar
Disorder increases the likelihood of developing depression. People with a
genetic susceptibility are more vulnerable to depression in the face of
- Recreational drugs/medication: Some drugs
(recreational and prescription) and alcohol can cause or exacerbate
depression. The reason is possibly because they interfere with the
regulation of brain chemicals or the physical structure of the brain
(excessive alcohol and sleeping tablets cause shrinkage of the brain).
- Medical illness: Illness including
strokes, Parkinson’s disease, Cushing's disease and thyroid disease, among
others, may be a contributory physiological factor.
Stressful life events (e.g. loss of a loved one, illness, financial worries) more often precede the first episode of mood disorders than subsequent episodes. It is believed that the initial episode in a mood disorder results in long-lasting changes in the biology of the brain (e.g. the functional state and interaction of neurotransmitters; also possibly a loss of neurones and a decrease in synaptic contacts). This increases the person's vulnerability to subsequent episodes.
A family’s style of interacting with different members, the family environment (e.g. a broken home) as well as its coping patterns may increase a vulnerability to a depressive disorder. An individual’s underlying personality type (e.g. dependent, obsessive compulsive) may also be a contributory factor.
reviewed by Dr Piet Oosthuizen, Dept. Psychiatry, University of Stellenbosch,
(Reviewed by Dr Stefanie van Vuuren, Psychiatrist, MB ChB (Stell), M Med (Psig)
(Stell), FC (Psych)SA, May 2011)