What Causes Anxiety? | Health and Life

Home

What Causes Anxiety?

Many people assume that anxiety arises from a traumatic event or overwhelming stress. It's true that experiences such as the death of a parent during childhood or another early trauma can play a significant role, but these kinds of events aren't always at the root of the problem.

Not everyone who has lived through a tragedy or terrifying occurrence develops an anxiety disorder, and not everyone who develops an anxiety disorder has endured such an ordeal. Research suggests that anxiety is partly genetic. Certain genetic variations may cause imbalances in brain chemistry that can predispose someone to anxiety. The biological tendency toward anxiety may be latent for years until an exceptionally stressful event triggers its expression. Personality factors may also play a role.

Genetic underpinnings

People with a parent or sibling who has had an anxiety disorder are at greater risk of developing one. For many years, experts debated whether this link was due to nature (a genetic predisposition that's passed from one generation to the next) or nurture (anxiety-provoking behaviors that are learned in families or are caused by stressful experiences growing up). It's now clear that these factors often interact.

Still, much is unknown, and the genetic factors are hardly straightforward. Researchers studying families with a history of anxiety disorders have scrutinized their genetic makeup in hopes of finding common features. Several candidates have been identified. Some are variants of genes, while others are regions on chromosomes that seem similar. But none of these genetic traits appears uniformly in people with anxiety disorders. Therefore it's unlikely that there's any single "anxiety gene." Many genes probably work together to induce the disorder.

One anxiety gene uncovered

So far, scientists have identified one anxiety-related gene in humans. This gene, called 5-HTT, regulates serotonin, a neurotransmitter that affects mood. A variation of this gene speeds the metabolism of serotonin by neurons (nerve cells), leaving less of the chemical available in the brain. Low levels of serotonin seem to be characteristic of anxiety disorders, depression, and other mental health disorders. One study found that this genetic variation was more than three times more common in people with generalized anxiety disorder than in people who did not have the disorder. It was also more prevalent in people with obsessive-compulsive disorder.

In a 2000 study in the Journal of Abnormal Psychology, researchers took blood samples from 72 people to see who had the 5-HTT gene variation. The participants then breathed a carbon dioxide–oxygen mix that causes shortness of breath, a sensation that sometimes provokes fearfulness and anxiety. The test provoked fear only among those with the genetic variation. It's important to note that none of the participants — even those with the gene variant — had symptoms of anxiety disorders before the experiment. Thus, the finding suggests that the 5-HTT gene variation doesn't cause anxiety by itself, but sets the stage for anxiety to develop in response to a sufficiently stressful situation.

More genes suspected

Researchers are currently investigating several other genes that may contribute to anxiety. A duplication on a region of chromosome 15 is especially common in families with high rates of panic disorder and phobia, according to a 2001 study in Cell. Potential genetic markers for panic disorder have also been found on chromosomes 1 and 11, and a possible marker for agoraphobia was found on chromosome 3.

Taken together, these findings amount to early evidence of a genetic basis for anxiety disorders. But because the study of genes related to anxiety is in its infancy, the particular genes involved and the ways in which their variations induce anxiety have yet to be uncovered. Thus far, no genetic tests are available to determine whether an individual is at higher risk for anxiety.

The brain

For decades, scientists have believed that anxiety results from abnormalities in brain chemistry. They base this conviction on the effects of drugs that reduce anxiety by increasing the availability of certain neurotransmitters in the brain. The first anti-anxiety drugs were benzodiazepines, which raise levels of the neurotransmitter gamma-aminobutyric acid (GABA). Later, drugs that increase serotonin levels and affect norepinephrine and other neurotransmitters associated with mood also proved effective. But these findings have raised even more questions. For example, what brain structures are involved? What malfunctions in the brain induce anxiety? And what role do neurotransmitters play?

Life experiences

People who are extremely anxious may think that a trying experience has given them reason to feel that way. And to a large degree, they're right.

Lingering effects

As mentioned earlier, a traumatic event is often a trigger for acute stress disorder, post-traumatic stress disorder, and specific phobias. Either of the two stress disorders usually begins within days of a terrifying experience. While a phobia may not develop immediately after a traumatic event, it can often be traced back to one. For example, many adults who fear dogs were attacked by dogs as youngsters.

There is growing evidence that highly stressful experiences, especially those that occur early in life, increase the risk for anxiety by impairing a person's ability to negotiate emotional bumps in the road later on. Such experiences include abuse or neglect, emotional deprivation, and the loss of or separation from one's mother. Studies show that rat pups separated from their mothers for just several minutes early in life have a much greater startle response than other pups when faced with stress several months later.

Traumas seem to alter the brain in a way that makes it more susceptible to anxiety. In addition to making the HPA axis hypersensitive (see "Hormones and the HPA axis"), they may also change the structure of the brain. The hippocampus, which works closely with the amygdala (the brain's "fear" center), is smaller in some people with post-traumatic stress disorder, as well as some who have endured extreme, prolonged stress (see "Hippocampus").

Acting in concert

Of course, not everyone who has survived a traumatic event develops an anxiety disorder. That's where an individual's genes and brain chemistry come in. One theory is that some people are genetically or biologically more susceptible to anxiety, but that it often takes a traumatic life event to serve as the catalyst. In the study of the 5-HTT gene (see "One anxiety gene uncovered"), people with a particular gene variation all developed anxiety symptoms only after facing a fear-inducing situation.

In some cases, the trauma or stress is not apparent. Some people seem to develop an anxiety disorder "out of the blue." But when they seek help, a mental health professional discovers clues suggesting an undiagnosed anxiety disorder experienced in childhood. For example, a 20-year-old with generalized anxiety disorder may have been a 3-year-old who had a hard time being away from her parents when they left for work (separation anxiety). However, trauma is not always a trigger. Some people who develop an anxiety disorder have not endured particularly stressful events.

2009-05-06