There has been much talk in the past few years about a possible connection between celiac disease and ADHD. Several studies have shown that children and adults with ADHD have a higher rate of celiac disease but another study indicated that there wasn't a significant difference.
What is Celiac Disease?
Celiac disease is an autoimmune disease that causes damage to the small intestine and interferes with how your body absorbs nutrients in foods. Those with celiac disease cannot tolerate gluten. This is found in wheat, rye and barley. Although it is most often thought of as in food, other products, such as medicines, vitamins and lip balms, can contain gluten.
For those with celiac disease, eating foods with gluten cause an immune system reaction - it begins to destroy villi, small fingerlike protrusions in the small intestine which help absorb nutrients in foods through the lining of the small intestine. When the villi are damaged, people become malnourished, no matter how much or what they eat.
Symptoms of celiac disease include:
- Bloating of the abdomen
- Abdominal pain
- Chronic diarrhea or constipation
- Pale, foul-smelling or fatty stool
- Weight loss, malnutrition
- Depression and anxiety
- Missed or irregular periods
Some people do not experience any of these symptoms but may still have long-term effects, such as liver disease and cancer of the intestine.
Research Showing a Link Between Celiac Disease and ADHD
Two studies have shown a strong association between celiac disease and ADHD. The studies showed that those with undiagnosed ADHD have a higher rate of celiac disease than the general population.
A study completed in 2011 at the Psychiatric Hospital of Rodewisch (Germany) looked at 67 people with diagnosed ADHD ranging in age from 7 to 42 years old. Ten of the participants tested positive for celiac disease and were put on a gluten-free diet for at least 6 months. Participants (or their parents) reported "significant improvement" in behavior and functioning and this was confirmed on questionnaires. Overall, celiac disease was found in 15 percent of those with ADHD, much higher than the 1 to 4 percent in the general population.
They believe that celiac disease should be included in the ADHD symptom checklist. 
A previous study, completed in 2006 looked at 132 patients with celiac disease. They were all screened for ADHD and found a high correlation between the two. Participants were put on a gluten-free diet and in this study, as the later one, behavior and functioning significantly improved.
Although the studies show a link between ADHD and celiac disease, it isn't clear whether celiac disease includes symptoms of inattention and hyperactivity or if having ADHD for some reason places you at a higher risk of also having celiac disease.
Study Negating Association Between ADHD and Celiac Disease
Researchers completing a study at Inonu University in Turkey reported that there is not a link between ADHD and celiac disease. This study was published in the Journal of Pediatric Gastroenterology and Nutrition in Feb. 2013. The study looked at 362 children and adolescents with ADHD between the ages of 5 and 15. Researchers found that the rates of celiac disease in those with ADHD were similar to rates of celiac disease in control groups (without ADHD.)
What Should You Do?
If you believe you or your child may have celiac disease and it may be contributing to ADHD symptoms, talk to your doctor. He can test for celiac disease and can tell you the next steps to take. Whether the test is positive or negative, however, you can try a gluten-free diet (it has to be completely gluten-free, not just reduced gluten) for 30 days to see if you notice a difference in behaviors or other ADHD symptoms. Be sure to talk with your doctor before, especially if you or your child is currently taking medication and you want to stop the medication during your gluten-free month.
For more information on gluten-free diets:
Nutrition and the Gluten-Free Diet
Is a Gluten-Free Diet a Cure to ADHD? A HealthCentral Explainer
Is a Gluten Free Diet Right for You?
Should you or Your Child try the GFCF (Gluten-free Casein-free) Diet?
 "Association of Attention-Deficit/Hyperactivity Disorder and Celiac Disease: A Brief Report," 201, H. Niederhofer, Primary Care Companian for CNS Disorders
"Celiac Disease," Updated 2012, Jan. 27, Staff Writer, National Institute of Diabetes and Digestive and Kidney Diseases
"Frequency of Celiac Disease in Attention-Deficit/Hyperactivity Disorder," 2013, Feb. S. Gungor et al, Journal of Pediatric Gastroenterology and Nutrition
"Range of Neurological Disorders in Patients With Celiac Diseas," 2004, Nathaniel Zelnik, Avi Pacht, Raid Obeid, Aaron Lerner, Pediatrics