Why are Gastrointestinal Problems Common in Autism?

Many children with autism spectrum disorder (ASD) have significant gastrointestinal (GI) problems, but doctors and scientists aren’t sure why. Our research team at the University of Missouri School of Medicine is on a mission to find out why in order to hopefully develop better treatments for these individuals.

Ask any parent of an individual with ASD, and they will likely tell you that their child experiences debilitating GI problems. In fact, research has shown that up to 90 percent of individuals with ASD experience some form of GI disturbance, such as constipation, irritable bowel syndrome, abdominal pain, and diarrhea. These GI issues commonly lead to pain and irritability, which also affects their child’s sleep. Furthermore, these issues can be even worse for people with ASD who are unable to speak, as they can’t communicate their pain to others.

Though many people with ASD have GI issues, the cause is not known, but recent research from our lab is beginning to shine some light on potential underlying causes.

The brain and the gut talk to each other through the wiring of the nervous system. One example of this interaction is when you feel “butterflies” in your stomach when you’re stressed. This is due to the “fight-or-flight” part of the nervous system, called the sympathetic nervous system, being activated.

Research has shown that the fight-or-flight response in ASD is heightened in some individuals, such that the brain makes the body, including the gut, think that it should prepare for battle.

This constant state of heightened stress is what we are focusing on as a potential cause of the GI issues in ASD.

Our lab at the MU Thompson Center for Autism & Neurodevelopmental Disorders has been studying the relationship between the body’s response to stressful things in the environment and GI symptoms for eight years.

Recent research from our lab, in conjunction with the Autism Speaks – Autism Treatment Network & Autism Intervention Research Network on Physical Health and Vanderbilt University looked at the relationship between the food that people with ASD eat, the vitamins and minerals contained in these foods, and how they may relate to their GI symptoms.

We asked the parents of 80 children and adolescents with ASD to tell us what foods their child ate, how much of each food, and how often they ate each food, over a one-month period. We also asked the parents to complete a questionnaire that assessed their child’s GI symptoms during the same one-month period.

During our analysis, we looked at the total amount of 32 different vitamins and minerals contained in the diets of the participants and how this related to the participant’s GI symptoms. We found that total levels of the vitamins and minerals were not associated with GI symptoms in these children. Surprisingly, things like fiber and water intake, which you might think would reduce constipation, did not reduce constipation in these children.

So what may be causing the GI problems in these children? Could some children with ASD suffer from GI distress due to a heightened stress response?

To test this hypothesis, we looked at levels of the stress hormone cortisol, which is released throughout the body when an individual is experiencing stress, before and after the same participants from above engaged in a stress test.

The stress test involved the participants putting their hands in cold water for a short period of time, which has been shown to cause a temporary stress response. To measure cortisol levels, we took small spit samples from the participants when they first came in to our lab and again after the stress test, and looked to see how large the change in cortisol levels were before the stress test and after.

Interestingly, we found that as the cortisol levels went up in response to the stress test, so did the child’s GI symptoms, especially for constipation. That means that the larger the child’s stress response was, the more constipation symptoms they had.

This is what we expected to see, especially since stress is associated with GI problems, even in people without ASD. However, this finding is important given that, as previously mentioned, up to 90 percent of people with ASD have GI symptoms.

So what now? From here, our lab is doing the next logical thing, which is to see what happens to GI symptoms in people with ASD when their stress response is blocked.

A class of drugs, called beta blockers, significantly reduce the response to stress. These drugs do this by sitting in receptors throughout the body that are looking for stress-causing neurotransmitters.

These beta-blocking drugs are typically prescribed to reduce heart rate and blood pressure, but have also been shown to help people with stage fright, such as actors and musicians. When an individual is under stress, the gut responds by slowing down the movement of stool, and so the stool piles up, leading to constipation.

However, beta-blockers reduce these stress signals throughout the body, including those sent to the gut from the brain. Going forward, our lab is testing out a beta-blocking drug in ASD to see how it affects GI symptoms.

Of course, the thought that beta blockers may help GI issues in ASD is only a hypothesis at this point, and the research must be carried out during a double-blinded (that is, neither the patient nor the doctor knows what drug the patient is taking), placebo-controlled clinical trial.

In summary, many people with ASD suffer from GI issues, and our laboratory is working to find out why. It may be that an increased stress response is to blame for these GI issues, as evidence from our lab suggests that this is the case.

However, dietary intake does not appear to be associated with GI issues in ASD. One possible treatment for GI issues in ASD may be the use of the stress-blocking drug, and a clinical trial is currently underway to test this hypothesis.