Researchers followed 1.92 million Danes, including 32,000 with ADHD, from birth through to 2013.
"In this nationwide prospective cohort study with up to 32-year followup, children, adolescents and adults with ADHD had decreased life expectancy and more than double the risk of death compared with people without ADHD," Soren Dalsgaard, from Aarhus University in Denmark, and his co-authors concluded in Wednesday's online issue of Lancet.
"People diagnosed with ADHD in adulthood had a greater risk of death than did those diagnosed in childhood and adolescence. This finding could be caused by persistent ADHD being a more severe form of the disorder."
Of the 107 individuals with ADHD who died, information on cause of death was available for 79. Of those, 25 died from natural causes and 54 from unnatural causes, including 42 from accidents.
Being diagnosed with ADHD along with oppositional defiant disorder, conduct disorder and substance use disorder also increased the risk of death, the researchers found.
Mortality risk was also higher for females than males, which led Dalsgaard to stress the need for early diagnosis, especially in girls and women, and to treat co-existing disorders.
Although talk of premature death will worry parents and patients, they can seek solace in knowing the absolute risk of premature death at an individual level is low and can be greatly reduced with treatment, Stephen Faraone, a professor of psychiatry and director of child and adolescent psychiatry research at SUNY Upstate Medical University in New York, said in a journal commentary published with the study.
Faraone noted two of the core symptoms of ADHD, inattention and impulsivity, would seem to be risk factors for accidents. A previous study by the Danish researchers suggested medications that reduce symptoms of inattention and impulsivity were associated with better performance in a driving simulator.
The editors of the Canadian Journal of Psychiatry argued there's been a "radical over-diagnosis" of mental illness and prescriptions compared with decades ago when treatment involved more psychotherapy.
Similarly, a commentary published in the Canadian Medical Association Journal said antipsychotic prescriptions to treat mood and behaviour disorders in children and youth has increased dramatically despite concerns about lack of efficacy and adverse events such as weight gain, diabetes and abnormal movements. It said the rise in prescriptions reflects complex societal, economic, political and cultural issues.