Serotonin Deficiency And Anxiety

Understanding serotonin deficiency and anxiety

What is serotonin?

Serotonin is a neurotransmitter. A neurotransmitter is a chemical messenger that carries signals, operating both inside the brain and other areas of the body. Serotonin is essential for us, given its implication in a wide range of bodily functions within the central nervous system.1 Within the human body, serotonin influences learning and memory, happiness and reward. For core physiological processes, serotonin is associated with regulating sleep, behaviour, and appetite.2

In relation to emotional regulation, serotonin is considered a ‘happy hormone’, as it plays a role in positive mood, emotions, and calmness. In turn, due to its involvement in such fundamental functions, serotonin is thought to play a pivotal role in some mental health conditions. More specifically, altered serotonergic activity in the forms of dysfunction, dysregulation, and deficiencies are particularly evident in anxiety, depression,and other mental and physical health conditions.3

Moreover, the brain’s serotonin system consists of a small collective of neurons located in a specific brain region: the raphe nuclei of the midbrain. Serotonin neurons within this system project extensively to other key brain regions involved in anxiety, such as the hippocampus, septum, amygdala, and prefrontal cortex.1 In all, this further supports just how significant a role serotonin plays in anxiety.

What is serotonin deficiency?

A serotonin deficiency is a lack of sufficient levels of serotonin within the body, and more specifically, the brain. This results in various negative repercussions. More explicitly, low serotonin levels are associated with various behavioural and emotional conditions. However, it should be noted that serotonin deficiency can affect people in a variety of ways.

Causes of serotonin deficiency

Researchers are unsure precisely what causes serotonin deficiency. However, some common potential causes or contributors include:

  • Genetic factors.
  • Hormone changes. 
  • Lack of physical activity. 
  • Chronic stress and/or pain.
  • Age-related health and brain changes. 
  • Nutritional deficiencies and/or digestion issues. 
  • Lack of exposure to sunlight or natural light.

Symptoms of serotonin deficiency

A serotonin deficiency has no definitive diagnostic criteria, meaning it is commonly discussed in terms of the resulting symptoms, as opposed to the exact blood levels of serotonin. Again, it remains unclear whether the symptoms cause the deficiency or whether the deficiency itself causes the symptoms. Overall, the symptoms of serotonin deficiency can be characterised as being either physical or psychological in nature.

Physical symptoms of serotonin deficiency include:

  • Pain perception – Experiencing chronic pain often without a clear physical origin.
  • Reduced bone density.1
  • Inflammation and immunity – The overall functioning of the immune system contributes to serotonin-related processes. 
  • Gastrointestinal symptoms – Issues with the digestive process as well as bowel movements and functions. 
  • Physical conditions – Serotonin deficiency is associated with physical conditions including obesity, diabetes, cardiovascular disease, fatigue, osteoporosis, and gastrointestinal issues.

Psychological symptoms of serotonin deficiency include:

  • Mood changes – Increased irritability or feeling down and excessively sad, often for no apparent reason.
  • Depression and anxiety. 
  • Aggression and impulsiveness. 
  • Cognition and attention – Serotonin affects one’s ability to concentrate and learn new information, meaning these abilities may be negatively impacted.
  • Sleep problems. 

Understanding anxiety

What is anxiety?

Anxiety is a normal stress response that typically operates on a self-regulatory basis. Experiencing anxiety is a normal part of life, but this primarily applies to instances where the anxiety is occasional, temporary, and self-correcting. In contrast, feelings of excess anxiety involve experiencing intense, excessive, and persistent fear about everyday situations that are disproportionate to the actual danger of the stressor. Consequently, individuals affected by anxiety disorders typically face a decreased quality of life, functional impairment, personal distress, and sometimes even maladaptive and irrational behaviour.4,5,6

Causes of anxiety

Researchers have yet to uncover the exact, definitive causes behind anxiety. However, they believe that a combination of biological and environmental factors contributes towards causing anxiety.7

Here are some of the causes of anxiety:

  • Environmental stressors
  • Neural circuitry – Faulty connections in the brain involving the HPA axis, which is associated with stress and is responsible for regulating fear and emotions, can lead to this axis failing to switch off. Its hyperactivity results in ongoing anxiety.9
  • Disrupted neurotransmitter functioning – Alterations in certain neurotransmitters, including serotonin, contribute towards anxiety.10
  • Anxiety disorders 
  • Other mental health conditions 
  • Certain health conditions or medical illnesses – Examples include irritable bowel syndrome, sleep disordersheart conditions, lung conditions, and thyroid conditions.11

Symptoms of anxiety

The general signs and symptoms of anxiety commonly experienced by individuals fall into four broad categories that include:

Somatic / Physical symptoms

– Cold or sweaty hands.

– Dry mouth.

– Muscle tension and/or chest pain.

– Blushing, sweating, or trembling.

– Increased heart rate (palpitations).

– Accelerated/deepened respiration (hyperventilation).

Emotional symptoms

– Sense of panic, dread, or terror.

– Feelings of impending doom.

– Restlessness and irritability.

– Sudden onset mood changes and increased emotionality.

Cognitive symptoms

– Anticipation of harm or losing control.

– Fear of dying and/or sense of unreality.

– Worried and ruminative thinking.

– Increased attentiveness (hypervigilance).

– Uncontrollable and obsessive thoughts.

– Problems concentrating or thinking beyond the present worry.

– Repetitive thoughts or flashbacks of traumatic experiences.

Behavioural symptoms

– Inability to sit still and remain calm.

– Exhibiting escape and avoidance behaviour.

– Displays of aggression and hostility.

– Ritualistic (often self-soothing) behaviours.

– Trouble sleeping.

The relationship between serotonin deficiency and anxiety

Serotonin is important in helping us regulate our moods.12 Altered serotonin activity can occur alongside mental health conditions such as anxiety. Meanwhile, medications used to promote serotonin levels have been shown to assist in combating these anxieties. Therefore, there is thought to be a link between serotonin and anxiety. 

It is thought that selective serotonin reuptake inhibitors, or SSRIs, such as fluoxetine, citalopram, escitalopram, sertraline and paroxetine help to manage anxiety and correct this serotonergic deficiency.13 SSRIs work by increasing the amount of serotonin available.

Overall, such evidence demonstrates the relationship between serotonin deficiency and anxiety.


Serotonin is a chemical messenger that operates within the brain and plays a pivotal role in various bodily and psychological functions. Therefore, serotonin deficiency brings with it many negative repercussions, including anxiety. With a serotonin deficiency, the brain is unable to regulate itself properly. Hyperactivity of the neural regions responsible for fear and emotion occurs, resulting in anxiety. Corroborating evidence of this relationship is provided by the effectiveness of selective serotonin reuptake inhibitors which work to correct serotonin deficiencies in order to help individuals manage their anxiety symptoms. Overall, serotonin deficiency can cause many undesirable effects.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Jaskirat Kanwal

Masters of Science – MSc, Applied Neuropsychology. University of Bristol, UK

Jaskirat currently works in pharmaceutical care and in the mental health sector. Given their extensive background in psychology, they’re currently seeking to undertake their DClinPsych. They hope to study further, and continue in academia and research, with hopes to ultimately become an HCPC registered clinical neuropsychologist.

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