Why am I depressed? The surprising link between anxiety and depression
By Anthony Berrick | January 28, 2018
What is depression?
Depression, known clinically as 'major depressive disorder', is a relatively common mood disorder affecting approximately 1 in 16 people in Australia in any given year.1
While it's common for people with depression to feel down or unhappy, depression is not simply the presence of depressed mood. Other painful emotions commonly associated with depression, like sadness, guilt, shame, worthlessness, and hopelessness, are also part of the normal human experience and are not necessarily symptoms of depression.
The American Psychiatric Association's diagnostic criteria2 for a diagnosis of major depressive disorder are:
- depressed mood most of the day, nearly every day;
- or loss of interest or pleasure in all, or almost all, activities most of the day, nearly every day;
- and at least four of the following symptoms:
- significant changes in appetite or weight;
- sleep disturbances;
- impairments related to movement and coordination;
- fatigue or loss of energy;
- feelings of worthlessness or guilt;
- difficulty thinking, concentrating or making decisions;
- recurrent thoughts of death or suicide.
Depression is diagnosed when a depressed mood, or the loss of interest or pleasure in nearly all activities, along with a range of additional symptoms listed above, occurs in a discrete episode lasting at least two weeks, leading to significant functional impairment in important areas of life (such as relationships or work) and 'clinically significant' distress.
There are many risk factors for depression, including an individual's learning history and stressful life events, genetic vulnerability, certain medical conditions, lifestyle factors, and drug and alcohol use, but a pre-existing anxiety condition seems to be particularly strongly linked to the development of depression.
Anxiety and depression
One of the most striking observations about depression is how frequently the condition occurs alongside an anxiety disorder. When two or more disorders occur together like this, they are described as being 'comorbid' conditions.
The stats show that about 85% of individuals with depression also experience significant symptoms of anxiety, while up to 90% of people diagnosed with an anxiety disorder also have comorbid depression.3
Looking at how depression and anxiety disorders develop over the course of an individual’s lifetime, it has been found that anxiety disorders are almost always the first condition to develop (usually around adolescence), and that the presence of an anxiety disorder substantially increases the risk for secondary depression.4
When it comes to predicting which individuals with an anxiety disorder might go on to develop depression, it is the number and severity of anxiety symptoms, rather than the specific type of anxiety diagnosis, which correlates most strongly with subsequent depressive symptoms.5
It's all about threat perception
One theory put forward to explain the link between anxiety disorders and depression concerns how these disorders are related to a person's sensitivity to perceived threats.
While immediate threats produce a fear response, and potential threats which are perceived to be avoidable elicit anxiety, potential threats which appear unavoidable evoke a depressed emotional state (see Figure 1, below).
Therefore, someone who has a genetically-inherited heightened sensitivity to threats, in general, would be more prone to developing anxiety disorders as well as depression.6
This theory is supported by twin and family studies (which attempt to examine the role of genetic make-up in the development of different disorders) which find that an inherited sensitivity to perceived threats accounts for approximately 30 to 40% of the likelihood of an individual developing both an anxiety disorder and depression.7
The theory makes a lot of sense when you consider how humans have evolved to respond to threats in the interest of survival. If you’re in immediate danger, the 'fight or flight' fear response is beneficial for survival as it prepares you for taking action to protect your life.
Likewise, if a potential threat (which is also seen to be potentially avoidable) looms in the future, the behaviours typically motivated by anxiety (e.g. avoidance, vigilance) can also help to prevent something bad from actually occurring.
However, when a potential threat is perceived to be unavoidable, it doesn’t make sense to waste energy and resources trying to overcome it, so ‘giving up’ (and thereby conserving resources) may actually be more helpful.
Still, perception is everything - what one person perceives to represent a threat, another may see as neutral or even positive. Furthermore, so-called threats are not necessarily even things that exist in the outside world - often someone with an anxiety disorder perceives their own private mental experiences (i.e. thoughts, feelings, memories, and sensations) as threats.
What this all means is that if you have depression as well as an anxiety condition, addressing your anxiety-related difficulties is likely to be crucial in order to effectively treat your depression.
1. Australian Bureau of Statistics (2007). National Survey of Mental Health and Wellbeing: summary of results. Canberra: ABS
2. American Psychiatric Association (2013). Diagnostic and statistical manual of mental disorders, 5th edition (DSM-5). Washington, DC, United States: American Psychiatric Publishing.
3. Gorman, J.M. (1997). Comorbid depression and anxiety spectrum disorders. Depression and Anxiety, 4, 160-168.
4. Wittchen, H.U., Kessler, R.C., Pfister, H., & Lieb, M. (2000). Why do people with anxiety disorders become depressed? A prospective-longitudinal community study. Acta Psychiatrica Scandinavica, 406, 14-23.
5. Coryell, W., Fiedorowicz, J.G., Solomon ,D., Leon, A.C., Rice, J.P., & Keller, M.B. (2012). Effects of anxiety on the long-term course of depressive disorders. British Journal of Psychiatry, 200, 210-215.
6. Gray, J. A., & McNaughton, N. (2000). The Neuropsychology of Anxiety. An Enquiry into the Functions of the Septo-Hippocampal System. Oxford University Press : Oxford.
7. Middeldorp, C. M., Cath, D. C., Van Dyck, R., & Boomsma, D. I. (2005). The co-morbidity of anxiety and depression in the perspective of genetic epidemiology. A review of twin and family studies. Psychological Medicine, 35, 611–624.