Large study finds links between adult ADHD and 34 out of 35 other diseases

A large study tracking some four million patients has linked adult ADHD with a higher risk of a wide range of other diseases, including nervous system, musculoskeletal, respiratory, gastrointestinal and metabolic conditions. Of 35 diseases studied, only arthritis was not found to be correlated.

ADHD (attention deficit hyperactivity disorder) is a mental health disorder drawing together a number of persistent symptoms including difficulty paying attention, hyperactivity and impulsive behavior. It’s reasonably common, with an estimated 4.4 percent of American adults currently diagnosed with ADHD, and many more suspected undiagnosed.

Researchers from the Department of Medical Epidemiology and Biostatics at the Karolinska Institutet in Stockholm pulled medical records for nearly 4.8 million Swedish people born between 1932 and 1995, concentrating on full sibling and maternal half-sibling pairs. They analyzed these people’s records for ICD (International Classification of Diseases) diagnoses, then used logistic regression modeling to estimate the associations between adult ADHD and 35 physical conditions, both in individuals and across sibling pairs.

Each association was expressed as an odds ratio (OR). The strongest associations were with alcohol-related liver disease (OR 4.70), sleep disorders (OR 4.62), chronic obstructive pulmonary disease (OR 3.24), epilepsy (OR 2.99), fatty liver disease (OR 2.94), and obesity (OR 2.67). Rheumatoid arthritis (OR 1.08) was the only condition found not to have a significant correlation. Results were similar between males and females, and no information on race was available.

The way these statistics are calculated, it’s not necessarily accurate to say an adult with ADHD is 4.62 times more likely to suffer from sleep disorders. It’s more accurate to say that patients diagnosed with sleep disorders were 4.62 times more likely to have an ADHD diagnosis as well. That’s an important distinction; some people don’t go to the doctor as much, so they don’t get diagnosed with as many conditions.

Another possible issue with the data here is that, as in many other places, adult ADHD diagnosis has only become common in Sweden in the past decade. Rates of diagnosis increased five-fold between 2004 and 2015, say the researchers. With patients in this study born as far back as the 1930s, only 1.3 percent of the study cohort had an ADHD diagnosis, suggesting that there were many undiagnosed cases potentially confounding the results.

Since ADHD is understood to be around 70-80 percent heritable, the researchers suspected underlying genetic conditions may be causing both the ADHD and the other conditions. And indeed, the results appeared to back this up. Full siblings of people with ADHD diagnoses also showed “significantly increased risk for most physical conditions,” and the effect was significantly stronger in full siblings than half-siblings.

The research team plans to do further work trying to understand the underlying mechanisms and risk factors in play, as well as the way ADHD might impact the management and prognosis of physical diseases in adults.

A paper on the research is open access in the Lancet.

Source: Karolinska Institutet

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