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Depression

In mid-2017, depression was identified as the leading cause of ill health and disability worldwide. It is clearly a major health and social problem, and a growing one.

An interesting feature of depression is that its prevalence varies substantially across the globe: it is far more common in Western than Eastern cultures. This implies that depression is to some extent determined by culture and environment, rather than – or in addition to – material wellbeing. Cultural origins for depression have important implications for treatment, which in Western medicine consists primarily of antidepressant medications.

In this article we explore the evidence on the causes and treatments for depression, and briefly examine some Australian responses to this highly prevalent condition.

What is depression?

The World Health Organization (WHO) defines depression as ‘persistent sadness and a loss of interest in activities that you normally enjoy, accompanied by an inability to carry out daily activities, for at least two weeks’. It can induce fatigue, changes in sleep or appetite, feelings of guilt or worthlessness, difficulty concentrating and suicidal thoughts.

Depression differs from mood fluctuations and short-lived emotional responses to everyday challenges, and becomes a serious health condition when it persists at moderate or severe levels. Depression can cause great suffering and impair people’s ability to function at work, in school, relationships and other aspects of life.

Depressive disorders are divided into two main diagnostic subcategories:

  • major depressive disorder / depressive episode – this involves symptoms such as depressed mood, loss of interest and enjoyment, and decreased energy; depending on the number and severity of symptoms, a depressive episode can be categorised as mild, moderate, or severe
  • dysthymia – a persistent or chronic form of mild depression with symptoms similar to depressive episode, but less intense and longer-lasting.

The epidemiology of depression

In 2015, more than 300 million people were estimated to be living with depression, 4.4 per cent of the global population. Their number has increased more than 18 per cent since 2005 (faster than the global population, which increased by nearly 13 per cent). Depression is also the major contributor to suicide deaths, which approach 800 000 per year.

In Australia, the estimated prevalence of depressive disorder is 5.9 per cent – higher than the global average. However, in 2011, 1.7 million people (7.8 per cent of the population) filled at least one prescription for antidepressant medications. Females were more likely than males to fill a prescription for antidepressant medications in 2011 (9.9 per cent vs 5.6 per cent), with rates of use increasing with age.

A review of population-based studies from 10 countries (the United States, Canada, Puerto Rico, France, Germany, Italy, Lebanon, Taiwan, Korea and New Zealand) – revealed great variation in rates of major depression. Lifetime rates ranged from 1.5 cases per 100 adults in Taiwan to 19.0 cases per 100 adults in Lebanon, and annual rates from 0.8 cases per 100 adults in Taiwan to 5.8 cases per 100 adults in New Zealand. Rates of major depression were higher for women than men in every country.

Causes of depression

There are physiological, genetic, psychological, social and demographic risk factors for the development of depression. Usually, no single factor will cause someone to become depressed.

Biological risk factors for depression include:

  • a family history of depression
  • long-term physical illness or injury
  • chronic pain
  • use of illicit drugs or some prescription medications
  • sleep problems
  • childbirth.

Psychological risk factors for depression include low self-esteem and a tendency for self-criticism.

Demographic and social risk factors for depression include:

  • being female
  • stressful life events (such as relationship conflict or caring for someone with an illness)
  • experiencing a difficult or abusive childhood
  • loneliness
  • being unemployed or having unfulfilling work.

An experience of depression is itself a risk factor for another depressive episode.

Evidence about the causes of depression

The extent to which the factors listed above contribute to the epidemic of depression in Australia and worldwide is difficult to determine. However, research shows that stress is a powerful factor in depression, either directly or by causing chemical changes in the brain. Unsurprisingly, given that depression is a form of mental illness, changes in the brain are often implicated as causal factors.

Slow generation of new neurons in the hippocampus might cause low mood. It has been hypothesised that mood only improves once nerves grow and form new connections, which takes several weeks. This idea is supported by the fact that antidepressants immediately boost the concentration of neurotransmitters in the brain, but depressed patients rarely improve until weeks or months afterwards. Moreover, animal studies have shown that antidepressants promote growth and branching of nerve cells in the hippocampus.

A now-venerable study (published in 1999, and verified since) used magnetic resonance imaging to study 24 women with a history of depression. The hippocampus (a brain region involved in processing long-term memory and recollection) was found to be 9–13 per cent smaller in depressed women than in the 24 case-matched controls. Moreover, the more episodes of depression a woman reported, the smaller her hippocampus.

Supporting the idea that depression is the natural outcome of unhappy events, a longitudinal study of female twins, involving 24 648 person-months of observation and 316 depressive episodes, showed that stressful life events have a strong causal relationship with the onset of major depression. Stress is known to suppress the production of neurons in the hippocampus and alter both synaptic plasticity and firing properties. In addition, a recent review of 88 studies involving 40 068 people found that loneliness was a significant but moderate predictor of depression.

Treatment of depression

Depression is often treated with antidepressant medications, which are now the most commonly used of all medications. Approximately 10 per cent of adult Australians take antidepressants daily, and prevalence of use has more than doubled since 2000 to be among the highest in the world (the second-highest in the OECD).

Christopher Davey and Andrew Chanen, writing in the Medical Journal of Australia in 2016, argued that the rapid increase in antidepressant use in Australia was driven by two factors:

  • the broadening of the diagnostic concept of depression in the third edition of the Diagnostic and statistical manual of mental disorders (DSM-III), published in 1980, which categorised the former two subtypes of depressive illness – a ‘neurotic’ illness that responded to psychological therapies, and a rarer melancholic depression with a biological cause that responded to medications – into a single ‘major depressive disorder’
  • the release of the first selective serotonin reuptake inhibitors (SSRIs) – notably fluoxetine (Prozac™) in 1986 – and ‘the ensuing cultural phenomenon that encouraged us to think of depression as resulting from a chemical imbalance that could be corrected with medication’.

Since the release of SSRIs in the mid-1980s, evidence has increasingly shown that they have – at best – only modest effects, in stark contrast to the initial claims of their manufacturers. High-quality research has revealed significant publication bias towards positive results in trials of 12 antidepressants approved by the United States Food and Drug Administration between 1987 and 2004. Of 74 registered studies, 31 per cent were never published; examination of those that were published suggests that 94 per cent of trials found the drugs were effective, whereas analysis of all 74 trials showed that only 51 per cent produced positive results.

Interestingly, the proportion of patients whose depression responds to a placebo (read more about this concept in the February 2017 issue of In Brief ) has increased steadily over the past two decades, narrowing the gap between response to antidepressant medication and placebo. However, there is good evidence that antidepressants are effective in preventing relapse of depression.

Other treatments for depression are cognitive behaviour therapy (CBT) and interpersonal psychotherapy (IPT). Recently published trials suggest that, like antidepressants, both are less effective than initially believed. Nevertheless, CBT is roughly as effective as antidepressant medication in treating depression.

Depression in rural Australia

Mental health has risen high on the national agenda in Australia in recent times as drought continues to put farming and rural communities under duress. On 5 August 2018, Prime Minister Malcolm Turnbull announced $190 million in additional drought relief funding, with part of these funds to be directed to mental health support.

Other responses to depression and related issues include The Ripple Effect, a project designed to help rural and regional people manage their own or others’ mental health and reduce the stigma associated with mental illness. It is a partnership between the National Centre for Farmer Health (NCFH), Deakin University, the Victorian Farmers’ Federation and several other concerned organisations. The NCFH Conference, to be held in Hamilton in mid-September,
is certain to have a strong focus on rural mental health.

Conclusions

Depression is a very common condition that causes considerable distress and illness. Numerous stressors are implicated in depression, and some people are genetically predisposed to develop it; cross-country comparisons suggest that cultural factors are also important, with prevalence being higher in Western countries. Treatment in Australia is largely focused on antidepressant medications, but non-drug approaches also exist. They may return to favour if emerging evidence continues to suggest that antidepressant drugs are much less potent than initially claimed.

Getting help

If you think you are depressed or have another mental health problem, help is available from:

  • your general practitioner
  • Lifeline – 13 11 14
  • Beyondblue – 1300 22 4636
  • About the author: Campbell Aitken
  • Dr Campbell Aitken is a freelance editor and a senior research fellow at the Burnet Institute.

If you would like to write an article for our Talking Points newsletter or In Brief blog, email Cassandra Hamilton (cassandrahamilton@westernalliance.org.au) or call 03 4215 2900.