A systematic review published this month found that people with attention-deficit/hyperactivity disorder are substantially more likely to report digestive problems than people without the condition, in what its authors call the first review devoted specifically to gastrointestinal symptoms in ADHD. The analysis, led by researchers at the University of Warwick and published in the Journal of Attention Disorders, pooled data from 23 studies covering more than 1.9 million people ages 2 to 65 across the United States, Sweden, Germany and South Korea.
Overall, people with ADHD had almost 50 percent higher odds of gastrointestinal symptoms than people without the diagnosis, according to the review, which was reported by ScienceDaily. Specific conditions showed sharper gaps: nearly double the odds of constipation, 58 percent higher odds of irritable bowel syndrome, and more than four times the odds of encopresis, or fecal incontinence, compared with people who do not have ADHD.
What might explain the link
The researchers say several explanations are plausible and not mutually exclusive: gastrointestinal side effects from stimulant and non-stimulant ADHD medications, impulsivity and irregular eating patterns associated with the condition, and differences in gut microbiome composition that some smaller studies have already flagged as part of a possible "gut-brain axis" in ADHD. This review is by far the largest tally of such evidence to date, drawing on studies conducted over roughly two decades in four countries, but it does not itself test any of those mechanisms or determine which, if any, best explains the association.
ADHD affects an estimated 5 to 7 percent of children and 2 to 3 percent of adults worldwide, and digestive complaints such as constipation and abdominal pain are already among the more common reasons children are referred to gastroenterologists. The new review suggests clinicians treating either condition may be more likely to encounter overlap than has generally been recognized.
We can't yet say ADHD causes these gut problems, or exactly what is driving the link, but the pattern is striking.
Saran Shantikumar, University of Warwick
The authors are explicit that their findings show an association, not proof of cause and effect. The underlying studies varied in design, diagnostic criteria and country, and the review could not separate the effects of ADHD itself from those of its treatment. The researchers are calling for further work to pin down the biological mechanisms, and in the meantime suggest that clinicians managing ADHD, and the families of those diagnosed with it, should also pay attention to digestive symptoms rather than treating them as unrelated.
