Serotonin & Bacteria in the Bowels Linked to Behavior Problems

biological link between autism and GI issues

Research is showing that serotonin and bacteria in the bowels may be linked to behavioral problems with autistic children. Constipation is a common cause of autistic children acting out because they often stop sleeping and eating well. They may become aggressive and frustrated because they have no other way of saying that their stomachs hurt.

Approximately one in 88 children in the U.S. has an autistic spectrum disorder. Up to 70 percent of them have gastrointestinal (GI) abnormalities at some point during childhood or adolescence. They are 3.5 times more likely to have constipation or chronic diarrhea than children who are not autistic. For years, parents have tried altering their children's diets to alleviate the issues, often restricting or completely eliminating gluten and dairy. But there is little scientific evidence supporting these dietary changes. Still signs keep pointing back to an underlying biological link between autism and GI issues.

A study published last year in the Journal of Abnormal Child Psychology linked the GI issues with behavior, showing that autistic children who have GI issues often experience extreme anxiety as well as regressions in behavior and communication skills. The side effects of the psychotropic drugs that are prescribed to many autistic children may be intensifying the digestive issues. Once the GI issues are treated, aggressive and problematic behaviors sometimes subside.

Scientists at U.C. Davis, supported by a $770,000 grant from Autism Speaks, are concentrating on bacterial overgrowth in the gut and potential antibiotic treatments that would help the gut function more normally. At the University of Toronto, neuroscientist Derrick MacFabe is researching the relationship between gut bacteria and brain development.

Serotonin is best known for its role in the central nervous system. It regulates mood, appetite, and sleep. More than 90% of the body's serotonin is in the gut. Dr. Michael Gershon, author of the The Second Brain: Your gut has a mind of its own and head of the gastroenterology lab at Columbia, was one of the first to study the role of serotonin in the gut -- or, as he calls it, the enteric nerve system. His research shows that serotonin regulates movement within the intestines, which is critical to healthy digestion.

A 2009 study found that about 30% of autistic children have too much serotonin. In medical terms, this is called hyperserotonemia. In the gut, serotonin is produced by two different enzymes. Once it is released, digestion kicks into action, and the serotonin needs to be reabsorbed for the gut to return to the normal resting state. Reabsorption is carried out mainly by the serotonin re-uptake transporter (SERT), which is carried in gene 17q11.2. If sufficient serotonin isn't produced, or it isn't reabsorbed, GI issues ensue.

Click here to read the full article "In Autism, the Importance of the Gut" on The Atlantic's website.

Click here to read "Reduced Incidence of Prevotella and Other Fermenters in Intestinal Microflora of Autistic Childrent" on PLOS ONE