Anxiety: Exploring the Biological Causes

According to the World Health Organisation 1 in 13 suffer from anxiety; a mental health illness categorised by severe feelings of worry and restlessness. There are many different types of anxiety disorder such as generalised anxiety disorder (GAD) where an individual has excessive irrational worry about activities, and social anxiety disorder which is characterised by feelings of fear in social situations. Anxiety disorders have many potential causes that can range from cognitive distortions (such as catastrophising) to social causes usually relating to a history of trauma, but I’ll be focussing solely on biological causes.

Neuroanatomy

Neuroanatomy is the first major biological cause of anxiety disorders. Those who suffer with anxiety tend to show high activity in the amygdala, a part of the brain associated with regulation of emotion, when presented with emotional stimuli. This overactivity of the amygdala causes anxiety due to overstimulation of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis (figure 1) involves three parts: the hypothalamus which is a portion of the brain that links the nervous system to hormonal messengers that communicate with the body; the pituitary gland which is a gland in the brain that releases hormones to communicate with the rest of the body, and the adrenal glands which are glands above each kidney. In the HPA axis the hypothalamus stimulates the pituitary gland that stimulates the adrenal gland to release cortisol (a stress hormone). Overstimulation of this circuit caused results in an excess of cortisol release which is linked with feelings of anxiety

Figure 1. The hypothalamic-pituitary-adrenal (HPA) axis. (Image adapted from crane medicine)

"When it comes to genetics considering the environment that an individual experiences is very important."

Genetics

The next biological cause is genetics. It has been found, using twin studies, that genetics have a 30-40% influence on anxiety. This means that anxiety can be passed through generations. However, when it comes to genetics considering the environment that an individual experiences is very important, as someone with genetic predispositions to anxiety may never develop anxiety if their environment doesn’t trigger it. There have been a number of genes directly linked to anxiety disorders, however many of the genes identified do not have well replicated findings. There are a few genes with exceptions to this, including the COMT gene. Mutations in this gene leads to a build up of dopamine which causes feelings of anxiety.

Substance-induced

The use of substances such as tobacco, opioids (such as some painkillers), stimulants (such as caffeine) and alcohol have been linked with causing and worsening anxiety. These substances usually improve anxiety in the short term but worsen anxiety in the long term. Furthermore, when these drugs wear off acute (intense and for a short duration) anxiety occurs. As an example of a substance’s effect on anxiety, alcohol worsens anxiety in the short term by changing the levels of serotonin and neurotransmitters in the brain. However, in the long term heavy drinking can cause individuals to be predisposed to anxiety.

Figure 2. Alcohol has been found to worsen and cause anxiety.

"Selective serotonin reuptake inhibitors (SSRI) are the most effective type of anxiolytic medication and it works by preventing serotonin reuptake by nerve cells."

Treatment

The biological treatment focuses around the use of anxiolytic (anxiety reducing) medication. This is prescribed by a GP and is usually used in conjunction with cognitive behavioural therapy (CBT). Selective serotonin reuptake inhibitors (SSRI) are the most effective type of anxiolytic medication and it works by preventing serotonin reuptake by nerve cells. This increase in serotonin has been found to reduce anxiety. Benzodiazepines are another drug used to treat anxiety however these are not recommended for routine use. These drugs act as a sedative and work by increasing the neurotransmitter GABA. An increase in GABA has been found to reduce the activity of regions of the brain associated with rational thought.