The links between anxiety and depression

Depression and anxiety disorders frequently co-exist. Among patients in the community who meet criteria for a clinical depression (i.e. major depression), approximately 50% will also be suffering from an anxiety disorder. In fact, in someone diagnosed with major depression, there is a three-fold to eight-fold greater likelihood that that person will also be suffering from a co-existing anxiety disorder.

Similarly, in persons with an anxiety disorder, the likelihood of developing major depression within the following year is very high (seven-fold to 62-fold risk). Put another way, the presence of an anxiety disorder is the single biggest risk factor for the development of depression.

Studies in the community confirm that depression and anxiety disorders occur at rates that exceed other common medical illnesses such as hypertension, diabetes, or asthma.

Further, patients with diagnosed medical illnesses, especially chronic conditions, are at a significantly increased risk for developing depression and/or anxiety disorders. Studies indicate that 20% to 50% of patients with many common medical illnesses (e.g. cancer, coronary artery disease, strokes) will develop depression. The rates for anxiety disorders are similar.

Which disorder comes first?
There has been a lot of interest among researchers to determine which disorder comes first, in the hope of clinicians intervening early to prevent the onset of the second disorder. Studies that have been done so far do not provide any clear answers. Only about two-thirds of patients with major depressive disorder and generalized anxiety disorder, social anxiety disorder, or posttraumatic disorder, have the onset of an anxiety disorder first. There are also no clear answers on whether the order of onset of the disorders affects the response to treatment.

What are the consequences?

• People with both anxiety and depression have more severe illness, higher rates of suicidality, suffer significantly more impairment in their work, social functioning, and have a poorer quality of life than persons without anxiety and depression.
• The co-existence of anxiety and depression often means a more chronic illness and a slower recovery. In a person with both conditions, there is also a greater chance that anxiety and/or depression will recur once the person has recovered.
• Because of the overlap of some of the symptoms in these disorders (e.g. sleep disturbance and loss of appetite), the presence of an anxiety disorder may mask their depression.
• The presence of a medical condition may also reduce the detection rate of depression and anxiety disorders. In fact, only one in every five patients who present with depression and anxiety and medical illness receives appropriate treatment for their psychiatric illness.
• The consequences of anxiety and depression not being recognised are serious and many, and include much higher rates of disability and more frequent doctor and clinic visits.

Treatment of co-existing anxiety and depression

• In people with both depression and an anxiety disorder, a combination of different treatment strategies (medication and psychotherapy) may be needed to improve the outcome of treatment.
• Cognitive-behaviour therapy is one treatment option that has been shown to be effective for both depression and anxiety disorders and can be used in combination with antidepressants, such as selective serotonin reuptake inhibitors (SSRIs).
• Because of the relative lack of treatment research on these co-existing disorders, to date no medication has been approved by the Food and Drug Administration (FDA) for the treatment of co-existing major depressive disorder and an anxiety disorder.
• However, SSRIs (e.g. citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline) and the serotonin norepinephrine reuptake inhibitor (e.g. venlafaxine) have become preferred medication treatments for co-existing major depression and anxiety. The SSRIs are indicated for a wide range of anxiety disorders including panic disorder, obsessive-compulsive disorder, posttraumatic stress disorder and social anxiety disorder, and they are also very effective in depression.
• Persons with anxiety may be particularly sensitive to some of the side-effects of the SSRIs (e.g. jitteriness) and generally need to be started on a lower dose of SSRI medication. However, the dose will need to be gradually increased over tine to get the desired effect.

Written by Dr Soraya Seedat, psychiatrist and co-director: MRC Unit on Anxiety Disorders.