Researchers at the University of Warwick have found a striking association between ADHD and digestive health after analyzing data from more than 1.9 million people across 23 studies.
Overall, people with ADHD were almost 50% more likely to experience gastrointestinal symptoms than people without ADHD. Some individual conditions showed even stronger associations. People with ADHD had nearly twice the odds of constipation, a 58% increase in irritable bowel syndrome, and more than four times the odds of encopresis (loss of bowel control).
Growing Evidence for an ADHD Gut Connection
ADHD is estimated to affect about 5% of children and 3-4% of adults worldwide, while reported diagnosis rates have increased sharply over the past four decades.
Digestive problems have already been well documented among people with autism spectrum disorder. At the same time, scientists have gathered increasing evidence for a ‘gut-brain axis’ that connects digestive health with neurodevelopmental conditions more broadly. Until now, however, researchers have had a less complete picture of how frequently gastrointestinal symptoms occur in people with ADHD.
The new study, published in the Journal of Attention Disorders, is the first systematic review devoted specifically to gastrointestinal symptoms in ADHD. Researchers brought together evidence from studies conducted in countries including the USA, Sweden, Germany and South Korea. Participants ranged in age from 2 to 65.
Co-lead Author Sarah Blake, a Medical Student at Warwick Medical School, said: “Almost every gut symptom we looked at: constipation, IBS, even indigestion, appeared to be associated with ADHD. These symptoms can have a real impact on daily life, but they could easily be overlooked if the focus is on ADHD itself.”
What Could Explain the Link?
Researchers do not yet know exactly why ADHD and digestive problems appear to be connected, but several possibilities could contribute.
ADHD-related traits such as impulsivity and irregular eating patterns may influence digestive health. Medications used to treat ADHD can also produce gastrointestinal side effects, including constipation.
Another possible factor involves the gut microbiome. Previous evidence has linked ADHD with differences in gut bacteria, which may influence communication between the digestive system and the brain through the vagus nerve, one of the body’s major pathways connecting the gut and brain.
Doctors May Need to Look Beyond ADHD Symptoms
The researchers say clinicians caring for people with ADHD should be aware that gastrointestinal symptoms may also be present and consider asking patients about digestive problems during appointments.
People experiencing more complicated gastrointestinal symptoms could also benefit from support from a dietitian or gastroenterologist.
Importantly, the findings identify an association rather than proving that ADHD itself causes digestive problems. More research will be needed to determine how much of the connection may involve underlying biological factors and how much could be related to medications or other influences.
Dr. Saran Shantikumar, Associate Clinical Professor, Warwick Medical School, said: “We can’t yet say ADHD causes these gut problems, or exactly what is driving the link, but the pattern is striking enough to warrant attention. Clinicians caring for people with ADHD may want to consider asking about gastrointestinal symptoms, particularly if they may be affecting quality of life.”
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