The Biology of Anxiety and Stress

Anxiety has both psychological and biological causes. While the two systems are intertwined, affecting each other mutually, it would appear that the more severe the anxiety then the more likely there is an underlying biological correlation.

Many theories exist to explain the underlying biology of anxiety/stress. While the different theories sound like they conflict, it may be that many causes of anxiety are acting together. At this point, science has not confirmed a single “smoking gun” in the biology of anxiety, so any or all or none of the theories could be true.

Understanding the Sympathetic Nervous System

The sympathetic nervous system (SNS) is the section of the brain that prepares the body for fight-or-flight, and is closely associated with anxiety. When the SNS is activated, our heart rate and breath rate go up, our eyes dilate, our blood vessels constrict and the bronchioles dilate. If there is a threat, we are super powered to handle it so that we can do our best, and then our system relaxes. If the threat is imagined, or if it is something we cannot directly address or resolve (such as traffic), then our system isn't able to relax after resolution and we are left in an anxious state. Anxiety disorder is when the SNS response never seems to relax. Long-term or chronic activation of the SNS can cause damage to the body, potentially affecting the heart, memory and more.

The Brain

The secret of anxiety may be locked within the structures of the brain. The amygdala, a small structure in the limbic (emotion) system of the brain, has the job of interpreting incoming information, sending signals to the sympathetic nervous system and also sending this information to the hippocampus, a memory area of the brain. The hippocampus will record the stimulus for future reference; this part of the brain may be involved in panic disorder, which is an anxiety disorder. In some cases, the hippocamus may cause a threat to be recorded improperly or as more of a threat than it actually is.

Daily Influences on Biology

Events or stimuli in our daily life can cause our anxiety level to rise temporarily. Anxiety can come from an immediate biological source or change in a daily event. For example, researchers at the University of Colorado found that if a toddler misses a single nap, their anxiety level rises noticeably.

Similarly, when some people drink a single cup of coffee they might feel increased anxiety for hours (while others may feel invigorated, and still others may feel nothing at all). Certainly, giving a public speech or standing in line to ride a big, scary roller coaster can cause anxiety levels to rise for a brief period.

Diet may also play a role in our anxiety levels. For example, the “comfort food” that many of us love and reach for in times of stress is pasta. Pasta is rich in carbohydrates, which helps to create serotonin a known anxiety reducer. The urge to eat that big bowl of pasta may in fact be a form of self-medication!

There are other simple things we can do to enhance our serotonin levels, which may help to biologically reduce our anxiety:

  • Exercise – said to increase serotonin
  • Meditation – said to increase serotonin
  • Sleep – affects serotonin levels and serotonin, in turn, affects sleep levels
  • Love and chocolate – both have been posited to raise serotonin levels

Another theory about serotonin as it relates to anxiety comes from researchers in Australia who believe that bacteria living in the gastro-intestinal tract can sometimes produce amines and toxins that interfere with neurotransmitters. Serotonin is produced in the gastrointestinal (GI) tract, for the GI tract, which might possibly affect the neurotransmitter in the brain.


It is recommended that people who tend to feel anxious avoid consuming things like caffeine, sugar and alcohol. In fact, there is a condition known as “caffeine-induced anxiety disorder,” which occurs when coffee consumption causes severe anxiety. Other things a person may consume might elicit feelings of anxiety. Some toxins, for example, can create anxiety as a symptom. Certain allergens can cause anxious feelings. Medications, most commonly cold medications, have been known to cause anxiety in some people. Prolonged use of marijuana can cause chronic anxiety or paranoia. There are drug interactions that can cause anxiety.

Genetics and Anxiety

Anxiety likely has a genetic correlation. Those with anxiety disorder, panic disorder and specific phobia all are more likely to have a close relative with the same disorder. It’s not clear whether the anxiety is learned from the family member as a response to stress or whether the persons’ biology predisposes them to the response. Recent twin studies, however, have indicated if one twin is found to have anxiety, the other twin is more likely to have anxiety, which lends more credence to the theory of a genetic link.

Some day researchers may find the location of anxiety on the human genome. Researchers in Barcelona found a difference in the DNA of those with anxiety disorder, specifically panic and phobic disorders. The 15th chromosome seemed to have a duplication. So the basis of anxiety disorders may go all the way down to the genes.

Medical Conditions

There are a number of medical conditions that cause anxiety. Some of these include endocrine conditions such as hypo/hyper thyroidism; cardiac conditions that include congestive heart failure; respiratory conditions such as chronic obstructive pulmonary disease (COPD); metabolic conditions such as B12 deficiency, and many others. The presence of anxiety might help a healthcare practitioner to diagnose any of these conditions if she is astute. In these circumstances, the condition should be treated first, and then the anxiety can be addressed as a separate problem.


There are anti-anxiety drugs available that work on neurotransmitters. Many patients have experienced good results with these medications, which reduce anxiety by manipulating these substances in the brain.

Serotonin is an important neurotransmitter. It is the main neurotransmitter implicated in the regulation of mood. Most of the anti-depressants currently in use target serotonin. Because serotonin also regulates appetite and sleep patterns, it’s not uncommon for people with anxiety to have disturbances in their eating and sleep patterns.

GABA, or gamma-aminobutyric acid, is another neurotransmitter researchers have targeted when designing medications for anti-anxiety therapy. Xanax, for instance, addresses GABA levels. GABA may quiet the signals from the amygdala (see “brain” above). When GABA levels are low, there may be too many signals firing in the brain, resulting in anxiety.

Monamine Oxidase (MAO) is yet another neurotransmitter implicated in anxiety. They seemed to be popular for treating social anxiety in particular. Drugs such as Nardil and Marplan work by reducing the amount of MAO in the brain.

It is important to remember that some stress and anxiety are natural and normal. When stress or anxiety become chronic or difficult to manage, it is advised that a healthcare professional is consulted to root out the cause and help determine an appropriate intervention.

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