What Causes Depression?

Cognitive Behavioural Therapy, or CBT, is an effective psychological treatment for psychological and emotional problems. As a psychiatrist in Edinburgh I see a lot of clients feeling low and unhappy. They often ask me if I think they're depressed, and what has caused them to feel like this. These questions have prompted me to write this short account.

The term "depression" means different things to different people. To psychiatrists, "depression" is synonymous with "clinical depression", a mental illness with a set of (numerous and rather loosely drawn) symptoms and it's own clinical course and prognosis. To most of the rest of us, "depression" simply means feeling very low.

Depression, in either sense of the term, is common. Statistics vary as to just how common it is, but a figure in the range of 50% for "life-long" risk of clinical depression is common. This means that most of us have a 1 in 2 chance of experiencing clinical depression in our lifetimes. Similarly, at any one time, between 10% and 20% of the adult population fulfil the criteria for clinical depression. These figures have been rising for many years now, and it is expected that they will continue to increase in the future. It can seem as if the world (particularly the industrialised part of it) is suffering an epidemic of depression.

The causes of such widespread and increasing frequency of depression are unclear and depend to a great extent on who you ask! What follows is a very brief summary of the main contenders. Many psychiatrists (and the pharmaceutical companies) focus on genetic and biochemical factors in depression - they emphasise the apparent hereditary nature of depression and the response of depression to antidepressants and Electro-Convulsive Therapy (ECT). They see depression as a physical disease of the brain.

In contrast, other researchers and workers (such as Social Theorists and Social Workers) emphasise the role of society and the immediate environment in causing depression. They hypothesise that a stressful living environment and detrimental social situation can cause depression. They point to differences in the rates of depression between different social groups (there are significantly higher rates of depression and suicide in lower socio-economic groups) as evidence of this environmental impact. Such a view issues in a very different set of "treatment" recommendations - not antidepressant tablets but socio-economic help such as improved housing and employment opportunities.

Finally , Cognitive Behavioural Therapy (or CBT) focuses on the individuals thinking as a potential cause of depression. The theory is that people prone to depression tend to habitually think in particular "depressive" ways, and when these people experience adverse events (or even simply believe that something bad has happened), then they are at great risk of becoming depressed. An example of a "depressive" thinking habit is "negative filtering", where a person will "see" or "count" only the unpleasant or bad things she experiences, and discount the good ones. A CBT therapist would call this pattern of thinking a "Thinking Error". Thinking in this way can make the world will seem threatening and yourself seem persecuted - and it's a small step from here to feeling depressed. A CBT therapist aims to help the person identify and change their "depressive" thinking habits.

As noted previously, the causes of depression are not known - we have some good hypotheses, but psychological and emotional problems are notoriously difficult to research and reach a definitive conclusion. And there are many more hypotheses out there - ranging from viral theories of depression to sunlight deprivation to dietary deficiencies.

Suffice to say that, given our current level of knowledge, it seems wise to accept that there are likely to be many causes of depression, either working alone or in tandem. Indeed, most Mental Health Practitioners use a "multi-factorial" model of mental illness that has room for physical, environmental (social) and psychological factors. The treatments offered for depression should (but, unfortunately, frequently don't) reflect this complexity. In particular, there remains a paucity of psychological treatments available on the NHS. Many clients that I see privately as a psychiatrist in Edinburgh have been unwilling to wait months before getting help.