September 27, 2023

A nationwide population study examines sleep problems in youth with ADHD

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.

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Swedish nationwide population study identifies top predictors of ADHD diagnoses among preschoolers

Most preschool-aged children diagnosed with ADHD also exhibit comorbid mental or developmental conditions. Long-term studies following these children into adulthood have demonstrated that higher severity of ADHD symptoms in early childhood is associated with a more persistent course of ADHD. 

The Study: 

Sweden has a single-payer national health insurance system that covers virtually all residents, facilitating nationwide population studies. An international study team (US, Brazil, Sweden) searched national registers for predictors of ADHD diagnoses among all 631,695 surviving and non-emigrating preschoolers born from 2001 through 2007.  

Preschool ADHD was defined by diagnosis or prescription of ADHD medications issued to toddlers aged three through five years old.  

Predictors were conditions diagnosed prior to the ADHD diagnosis. 

A total of 1,686 (2.7%) preschoolers were diagnosed with ADHD, with the mean age at diagnosis being 4.6 years. 

The Numbers:

Adjusting for sex and birth year, the team reported the following predictors, in order of magnitude: 

  • Previous diagnosis of autism spectrum disorder increased subsequent likelihood of ADHD diagnosis twentyfold. 
  • Previous diagnosis of intellectual disability increased subsequent likelihood of ADHD diagnosis fifteenfold. 
  • Previous diagnosis of speech/language developmental disorders and learning disorders, as well as motor and tic disorders, increased subsequent likelihood of ADHD diagnosis thirteen-fold. 
  • Previous diagnosis of sleep disorders increased subsequent likelihood of ADHD diagnosis fivefold. 
  • Previous diagnosis of feeding and eating disorders increased subsequent likelihood of ADHD diagnosis almost fourfold. 
  • Previous diagnosis of gastroesophageal reflux disease (GERD) increased subsequent likelihood of ADHD diagnosis 3.5-fold. 
  • Previous diagnosis of asthma increased subsequent likelihood of ADHD diagnosis 2.4-fold. 
  • Previous diagnosis of allergic rhinitis increased subsequent likelihood of ADHD diagnosis by 70%. 
  • Previous diagnosis of atopic dermatitis or unintentional injuries increased subsequent likelihood of ADHD diagnosis by 50%. 

The Conclusion: 

This large population study underscores that many conditions present in early childhood can help predict an ADHD diagnosis in preschoolers. Recognizing these risk factors early may aid in identifying and addressing ADHD sooner, hopefully improving outcomes for children as they grow

July 2, 2025

Northern Finnish Population Study Finds ADHD Slashes Higher Education Attainment, Comorbidity of ADHD + ODD much worse

Background:

Although ADHD typically begins in childhood, its symptoms frequently continue into adulthood, and it is widely acknowledged as having a lifelong prevalence for most persons with ADHD. 

ADHD symptoms are linked to poor academic performance, mainly due to cognitive issues like compromised working memory. These symptoms lead to long-term negative academic outcomes and difficulty in achieving higher educational degrees. 

Oppositional Defiant Disorder (ODD) often co-occurs with ADHD. In community samples, it appears in about 50–60% of those with ADHD. ODD symptoms include an angry or irritable mood, vindictiveness toward others, and argumentative or defiant behavior that lasts more than 6 months and significantly disrupts daily life.  

Since ODD tends to co-occur with ADHD, research on pure ODD groups without ADHD is limited, especially in community samples. This longitudinal study aimed to examine the impact of ADHD and ODD symptoms in adolescence on academic performance at age 16 and educational attainment by age 32. 

Study:

Finland, like other Nordic countries, has a single-payer health insurance system that includes virtually all residents. A Finnish research team used the Northern Finnish Birth Cohort to include all 9,432 children born from July 1, 1985, through June 30, 1986, and followed since then. 

ADHD symptoms were measured at age 16 using the Strengths and Weaknesses of ADHD symptoms and Normal-behaviors (SWAN) scale. 

Symptoms of ODD were screened using a 7-point rating scale similar to the SWAN scale, based on eight DSM-IV-TR criteria: “Control temper”, “Avoid arguing with adults”, “Follow adult requests or rules”, “Avoid deliberately annoying others”, “Assume responsibility for mistakes or misbehaviour”, “Ignore annoyances from others”, “Control anger and resentment”, and “Control spitefulness and vindictiveness.” 

Higher education attainments were determined at age 32. 

Results:

After adjusting for the educational attainments of the parents of the subjects, family type, and psychiatric disorders other than ADHD or ODD, males with ADHD symptoms at age 16 had a quarter, and females a little over a third, of the higher education attainments of peers without ADHD symptoms at age 32.  

With the same adjustments, males with ODD symptoms alone had two-thirds, and females 80%, of the higher education attainments of peers without ODD, but neither outcome was statistically significant. 

However, all participants with combined ADHD and ODD symptoms at age 16 had roughly one-fifth of the higher education attainments of peers without such symptoms upon reaching age 32. 

Interpretation: 

The team concluded, “The findings that emerged from this large longitudinal birth cohort study showed that the co-occurrence of ODD and ADHD symptoms in adolescence predicted the greatest deficits of all in educational attainment in adulthood.” 

This study highlights the significant, long-lasting impact that co-occurring ADHD and ODD symptoms can have on educational outcomes well into adulthood. It underscores the importance of addressing both disorders together during adolescence to help improve future academic success.

July 1, 2025

U.S. Nationwide Study Finds Down Syndrome Associated with 70% Greater Odds of ADHD

The Background:

Down syndrome (DS) is a genetic disorder resulting from an extra copy of chromosome 21. It is associated with intellectual disability. 

Three to five thousand children are born with Down syndrome each year. They have higher risks for conditions like hypothyroidism, sleep apnea, epilepsy, sensory issues, infections, and autoimmune diseases. Research on ADHD in patients with Down syndrome has been inconclusive. 

The Study:

The National Health Interview Survey (NHIS) is a household survey conducted by the National Center for Health Statistics at the CDC. 

Due to the low prevalence of Down syndrome, a Chinese research team used NHIS records from 1997 to 2018 to analyze data from 214,300 children aged 3 to 17, to obtain a sufficiently large and nationally representative sample to investigate any potential association with ADHD. 

DS and ADHD were identified by asking, “Has a doctor or health professional ever diagnosed your child with Down syndrome, Attention Deficit Hyperactivity Disorder (ADHD), or Attention Deficit Disorder (ADD)?” 

After adjusting for age, sex, and race/ethnicity, plus family highest education level, family income-to-poverty ratio, and geographic region, children and adolescents with Down syndrome had 70% greater odds of also having ADHD than children and adolescents without Down syndrome. There were no significant differences between males and females. 

The Take-Away:

The team concluded, “in a nationwide population-based study of U.S. children, we found that a Down syndrome diagnosis was associated with a higher prevalence of ASD and ADHD. Our findings highlight the necessity of conducting early and routine screenings for ASD and ADHD in children with Down syndrome within clinical settings to improve the effectiveness of interventions.” 

June 27, 2025