September 27, 2023
Denmark has a universal health insurance system that requires tracking all health care data in a system of national registries. That makes it possible to explore what's going on in an entire national population, rather than have to rely on sampling a small part of it, and hoping the sampling is reasonably representative.
A team of Danish researchers used the Civil Registration System to identify all single births through 1993 through 2014 and linked those records to corresponding records in the Psychiatric Central Research Register and National Patient Register for the years 2011through 2016. There were 1,397,850 youths in that cohort, of whom 12,844 were diagnosed with ADHD during the study period.
At five years of follow-up after diagnosis, almost three in ten youths with ADHD (29 percent) had registered evidence of sleep problems (including the use of melatonin, which is by prescription only in Denmark). For those with concomitant conduct disorder, almost half (45 percent) had registered evidence of sleep problems.
In the general population, on the other hand, the cumulative risk of sleep problems at five years of follow-up varied from one in a hundred for children followed from age 5 or age 10 to one in forty for those followed from age 15.
After adjusting for the confounding effects of three other neurodevelopmental disorders - autism spectrum disorder, oppositional defiant disorder/conduct disorder, and epilepsy- youths with ADHD were still roughly 23 times more likely to have sleeping problems than were normally developing youths.
The authors cautioned, however, that the low rate of sleep problems in the general population "may indicate that sleeping problems without coexisting neurodevelopmental disorders are generally diagnosed or treated in primary health care (and hence not included in our study)."
A further limitation, they added, is that "we can not exclude the possibility of residual confounding. Thus, it remains unclear whether neurodevelopmental disorder contributes to the sleep problem or whether certain unmeasured characteristics of children with neurodevelopmental disorders may explain the apparent association with sleep problems."
Allan Hvolby, Jakob Christensen, Christiane Gasse, Soren Dalsgaard, Julie Werenberg Dreier, "Cumulative incidence and relative risk of sleep problems among children and adolescents with newly diagnosed neurodevelopmental disorders: A nationwide register-based study," Journal of Sleep Research (2020), https://doi.org/10.1111/jsr.13122.