ArticlesMortality in children, adolescents, and adults with attention deficit hyperactivity disorder: a nationwide cohort study
Introduction
Many mental disorders are associated with shortened life expectancy,1 but little is known about whether this association occurs for attention deficit hyperactivity disorder (ADHD). However, ADHD is known to be associated with several factors that are likely to affect mortality rates. In the USA and Europe, the most common cause of death in childhood is unintentional injury,2 and children with ADHD have an increased risk of sustaining injuries.3 Similarly, adults with ADHD are at increased risk of serious traffic accidents.4 ADHD is also associated with substance use disorder,5 criminality,6, 7, 8 and development of more severe mental disorders,9, 10 which might affect life expectancy. Comorbid oppositional defiant disorder and conduct disorder have previously been shown to be among the strongest and most negative prognostics in children and adolescents with ADHD, significantly increasing the risk of later development of psychotic disorders11 and substance use disorder,5 and risk of committing crime.6
Thus, many reasons exist to believe that ADHD is associated with increased risk of early death. However, to our knowledge, only one study12 has compared the mortality of individuals with ADHD with that of population controls. The results suggested increased mortality among 367 individuals with ADHD (standardised mortality ratio 1·88, 95% CI 0·83–4·26, p=0·13), which we believe did not reach significance because of statistical power limitations.12 Whether ADHD is associated with increased mortality therefore remains unknown.
To compare the risk of a rare event, such as premature death, in individuals with ADHD with healthy controls, a large sample size with long follow-up is needed. The longitudinal Danish registers offer such an opportunity.13, 14, 15, 16 In the present prospective follow-up study of a nationwide birth cohort, we aimed to estimate excess all-cause mortality in children, adolescents, and adults with ADHD. Additionally, we examined the added effect of comorbid oppositional defiant disorder, conduct disorder, and substance use disorder on mortality rates in individuals with ADHD.
Section snippets
Study population
All people living in Denmark from 1968 onwards are registered in The Danish Civil registration System.16 For each person registered, the system includes a ten-digit personal identification number (PIN) and information on sex, date and place of birth, vital status (continuously updated), and parents' personal identifiers. The PIN is used in all national registers, enabling accurate linkage of data between registers at an individual level. Our study cohort included all children born in Denmark
Results
We followed up 1 922 248 individuals up to a maximum age of 32 years, from their first birthdays or Jan 1, 1995 (whichever came last) until death, emigration from Denmark, or June 30, 2013 (whichever came first). We included 24 907 560 person-years in the study. In 44 883 (2·3%) children and adolescents, follow-up was ended before the end of the study (June 30, 2013) because of emigration from Denmark (44 009 individuals) or because they were lost to follow-up (874 individuals). During
Discussion
In this nationwide prospective cohort study with up to 32 year follow-up, children, adolescents, and adults with ADHD had decreased life expectancy and more than double the risk of death compared with people without ADHD. The risk seemed to be highest within the first 5 years of diagnosis of ADHD (crude MRRs 2·45–3·75), but even after more than 10 years, the mortality rate was still almost doubled (1·9). Additionally, mortality rate significantly depended on age at first ADHD diagnosis. People
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