What causes depression?

The causes of depression aren’t fully known, although we do know some of the factors that can increase your risk (see below).

Is low serotonin to blame?

Brain cells and serotonin

Cells in your brain (neurons) send signals to each other by releasing ‘messenger chemicals’ such as serotonin.
Image: Nobeastsofierce/Shutterstock.com

Serotonin is one of the neurotransmitters (messenger chemicals) that transmit signals between cells in your brain. Serotonin, along with other neurotransmitters such as noradrenaline and dopamine, are involved in mood and emotions. However, their role in causing depression is not fully understood, and it is likely that other brain chemicals or systems are also involved.

Antidepressants increase the amount of certain neurotransmitters, and this is how they are thought to reduce the symptoms of depression. But depression is more complicated than just having low serotonin.

Who can get depression?

Anyone can get depression, but you are more likely to get it if you have any of these risk factors:

  • a family history of depression
  • difficult social circumstances, e.g. homelessness, unemployment or chronic illness
  • bad childhood experiences, e.g. abuse or neglect
  • some personality traits; e.g. disliking yourself, fearing the worst or being easily bothered by things
  • not having a relationship with someone you can confide in.

Women are at higher risk of depression than men. Overall, 15% of women and 9% of men aged 18–85 years have had depression at some point in their lives.

In many cases, these risk factors combine with stressful life events, such as relationship breakdown or the loss of a loved one, and result in depression. But depression doesn’t always stick to these rules — some episodes of depression happen without any stressful life event, and many stressful life events don’t trigger depression even in those who have other risk factors. We do know that having a supportive and confiding relationship can protect you from depression after a stressful life event.

Other conditions that increase the risk of depression

Some other chronic diseases increase the risk of depression, for example heart disease and diabetes.

Having depression at the same time as one of these conditions can increase the risk of complications from it. The reasons for this are not completely clear. However, getting effective treatment for your depression helps. In one study of people with depression plus another illness, those who were treated for their depression coped better because they had a lower burden of symptoms from their other illness. They also had better quality of life and overall adaptation to the other illness.

Find more information

  • Malhi GS, Parker GB, Greenwood J. Structural and functional models of depression: from sub-types to substrates. Acta psychiatr Scand 2005;111:94–105.[PubMed]
  • National Collaborating Centre for Mental Health. Depression: the NICE guideline on the treatment and management of depression in adults (updated edition). London: National Institute for Health and Clinical Excellence, 2010. www.nice.org.uk/nicemedia/live/12329/45896/45896.pdf (accessed 9 February 2012). 
  • Australian Institute of Health and Welfare. Prevention of cardiovascular disease, diabetes and chronic kidney disease: targeting risk factors. Cat. no. PHE 118. Canberra: AIHW, 2009. www.aihw.gov.au/publication-detail/?id=6442468313&tab=2 (accessed 22 February 2012). 
  • Ellis P; Royal Australian and New Zealand College of Psychiatrists Clinical Practice Guidelines Team for Depression. Australian and New Zealand clinical practice guidelines for the treatment of depression. Aust N Z J Psychiatry 2004;38:389–407. www.ranzcp.org/images/stories/ranzcp-attachments/Resources/Publications/CPG/Clinician/CPG_Clinician_Full_Depression.pdf (accessed 22 February 2012).
  • Katon WJ. Epidemiology and treatment of depression in patients with chronic medical illness. Dialogues Clin Neurosci 2011;13:7–23. [PubMed Central] (accessed 22 February 2012).