September 14, 2023
Taiwan's single-payer National Health Insurance system encompasses its entire population, and it's National Health Insurance Research Database tracks all medical claims in the system. That makes it easy to conduct nationwide population studies.
Two Taiwanese research teams availed themselves of that database to explore in-depth a surprising relationship between the birth month of children and rates of ADHD diagnosis.
In principle, the two should be unrelated. The likelihood of diagnosis should be the same regardless of the month a child is born. But the data are clear that this is not so. Children born late in summer are the most likely to be diagnosed with ADHD, and those in autumn are the least likely.
Using a nationwide database of over 29 million persons, one of the teams (Hsu et al.) found that children born in April were 6% more likely to be diagnosed with ADHD than the year-round mean, those in May 12% more likely, those in June 20% more likely, and those in July and August well over 25% more likely.
Conversely, children born in September were 19% less likely to be diagnosed with ADHD than the year-round mean, followed by a gradual increase in likelihood with each succeeding month until the following September.
The second team (Chen et al.) analyzed some 9.5 million children and adolescents in the same reserch database, and found that those born in August were 67% more likely to be diagnosed with ADHD than those born in September, after adjusting for age, sex, residence, and income. August births were also almost twice as likely (80% more likely) as September births to be on long-term treatment with ADHD medications.
The first team also performed a meta-analysis of eleven studies with a combined total of over 580,000 participants in North America (the U.S. and Canada), Europe (U.K., Germany, Norway, Sweden, Denmark), Asia (China, Taiwan, South Korea), and Oceania (Australia). Children born in the summer (June through August) were 13% more likely to be diagnosed with ADHD than the year-round mean, whereas those born in autumn were 13% less likely to be diagnosed with ADHD. This confirms that this pattern is not confined to Taiwan. It is worldwide.
Note carefully that the sharp discontinuity between August and September corresponds with the break-of point that decides which children get assigned to which school class. Anyone who turns a certain age by the start of the school year in September is included in the class associated with that age, whereas those turning the same age later are held back in the following class. That means that in any given class, those born in September are the oldest children and those born in August the youngest.
As signaled earlier, the likelihood of an ADHD diagnosis should be independent of something as obviously arbitrary as a birth month. That suggests there may be an unconscious bias trending against younger students when it comes to diagnosis.
Chen et al. concluded, "The effect of relative age on diagnoses and prescriptions was determined to last from childhood to adolescence but attenuated with age. Relative age is an indicator of brain maturity in cognition, behavior, and emotion and may thus play a critical role in the likelihood of being diagnosed as having childhood mental disorders and subsequently being prescribed psychotropic medication. Therefore, clinicians should consider the relative age effect in the childhood mental health care context."
Mu-Hong Chen, Kai-Lin Huang, Ju-Wei Hsu, Shih-Jen Tsai, Tung-Ping Su, Tzeng-Ji Chen, Ya-Mei Bai, "Effect of relative age on childhood mental health: A cohort of 9,548,393 children and adolescents," Acta PsychiatricaScandinavica (2021), online ahead of print, https://doi.org/10.1111/acps.13327.
Chih-Wei Hsu, Ping-Tao Tseng, Yu-Kang Tu, Pao-Yen Lin, Chi-Fa Hung, Chih-Sung Liang, Yun-Yu Hsieh, Yao-Hsu Yang, Liang-Jen Wang, Hung-YuKao, "Month of birth and mental disorders: A population-based study and validation using global meta-analysis," Acta Psychiatrica Scandinavica (2021), online ahead of print, https://doi.org/10.1111/acps.13313.
The National Health Interview Survey (NHIS) is conducted annually by the National Center for Health Statistics at the Centers for Disease Control and Prevention. The NHIS is done primarily through face-to-face computer-assisted interviews in the homes of respondents. But telephone interviews are substituted on request, or where travel distances make in-home visits impractical.
For each interviewed family, only one sample child is randomly selected by a computer program.
The total number of households with a child or adolescent aged 3-17 for the years 2018 through 2021 was 26,422.
Based on responses from family members, 9.5% of the children and adolescents randomly surveyed throughout the United States had ADHD.
This proportion varied significantly based on age, rising from 1.5% for ages 3-5 to 9.6% for ages 6-11 and to 13.4% for ages 12-17.
There was an almost two-to-one gap between the 12.4% prevalence among males and the 6.6% prevalence among females.
There was significant variation by race/ethnicity. While rates among non-Hispanic whites (11.1%) and non-Hispanic blacks (10.5%) did not differ significantly, these two groups differed significantly from Hispanics (7.2%) and Others (6.6%).
There were no significant variations in ADHD prevalence based on highest education level of family members.
But family income had a significant relationship with ADHD prevalence, especially at lower incomes. For family incomes under the poverty line, the prevalence was 12.7%. That dropped to 10.3% for family incomes above the poverty level but less than twice that level. For all others it dropped further to about 8.5%. Although that might seem like poverty causes ADHD, we cannot draw that conclusion. Other data indicate that adults with ADHD have lower incomes. That would lead to more ADHD in kids from lower income families.
There was also significant geographic variation in reported prevalence rates. It was highest in the South, at 11.3%, then the Midwest at 10%, the Northeast at 9.1%, with a jump down to 6.9% in the West.
Overall ADHD prevalence did not vary significantly by year over the four years covered by this study.
This study highlights a consistently high prevalence of developmental disabilities among U.S. children and adolescents, with notable increases in other developmental delays and co-occurring learning and intellectual disabilities from 2018 to 2021. While the overall prevalence remained stable, these findings emphasize the need for continued research into potential risk factors and targeted interventions to address developmental challenges in youth.
It is also important to note that this study assessed the prevalence of ADHD being diagnosed by healthcare professionals. Due to variations in healthcare accessibility across the country, the true prevalence of ADHD may differ still.
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Background:
An international research team used the nationally representative 2020–2021 U.S. Survey of Children’s Health to explore associations between ADHD, weeknight sleep insufficiency, and bedtime irregularity.
"Sleep sufficiency" refers to the recommended amount of sleep for an individual. Sleep recommendations vary by age and other factors, such as health and lifestyle. For example, 7-9 hours is typically considered sufficient sleep for most adults, but an active teen may require closer to 10 hours of sleep per day.
Previous studies have shown that issues with both falling and staying asleep are common in individuals with ADHD.
The Study:
The team matched 7,671 children and adolescents with ADHD aged 3-17 to 51,572 controls.
Noting that “The few available population-based studies examining sleep in children with ADHD have focused on circumscribed age ranges, limiting generalizability across childhood, and have seldom included controls,” and “bedtime irregularity has received limited empirical attention in children with ADHD,” this study focused on these aspects of sleep impairment.
The study group excluded children and adolescents with ADHD with Down syndrome, current or lifetime cerebral palsy, and current or lifetime intellectual disability. In the control group, it excluded individuals with Down syndrome, cerebral palsy, intellectual disability, speech and language disorder, autism spectrum disorder, ADHD, anxiety, depression, behavioral or conduct problems, Tourette syndrome, and use of mental health services in the preceding 12 months. These groups were excluded to limit potential confounding factors.
After adjustment for covariates, parents of children and adolescents with ADHD reported weekday sleep insufficiency 65% more frequently than parents of controls.
However, when comparing matched controls with children and adolescents with ADHD who were being treated with ADHD medication, there was no significant difference.
Similarly, there was a small but significant effect size increase in bedtime irregularity among children and adolescents with ADHD relative to their matched controls.
Yet there was also a small but significant effect size decrease in bedtime irregularity among those taking medication for ADHD relative to those who were unmedicated.
The team noted, “Interestingly, here, ADHD medication use was linked to less bedtime irregularity across full and age-stratified samples, and not related to sleep insufficiency. However, research indicates the association between stimulant use and sleep problems is attenuated with longer duration of use, and also suggests the potential for stimulants to produce positive effects on sleep through reduced bedtime resistance. Further, ADHD medication type, not specified, may have influenced outcomes.”
The Take-Away:
The study concluded that ADHD in children was linked to insufficient sleep and irregular bedtimes in a nationally representative sample, reinforcing and expanding previous research. The findings emphasize the influence of various factors on sleep insufficiency and bedtime irregularity, including race, screen time, poverty, ADHD severity, and depression.
Noting that “the association between adult ADHD and dementia risk remains a topic of interest because of inconsistent results,” an Israeli study team tracked 109,218 members of a nonprofit Israeli health maintenance organization born between 1933 and 1952 who entered the cohort on January 1, 2003, without an ADHD or dementia diagnosis and were followed up to February 28, 2020.
Israeli law forbids nonprofit HMOs from turning anyone away based on demographic factors, health conditions, or medication needs, thereby limiting sample selection bias.
The estimated prevalence of dementia in this HMO, as diagnosed by geriatricians, neurologists, or psychiatrists, is 6.6%. This closely matches estimates in Western Europe (6.9%) and the United States (6.5%).
The team considered, and adjusted for, numerous covariates: age, sex, socioeconomic status, smoking, depression, obesity, chronic obstructive pulmonary disease, hypertension, atrial fibrillation, heart failure, ischemic heart disease, cerebrovascular disease, diabetes, Parkinson’s disease, traumatic brain injury, migraine, mild cognitive impairment, psychostimulants.
With these adjustments, individuals diagnosed with ADHD were almost three times as likely to be subsequently diagnosed with dementia as those without ADHD. Men with ADHD were two and a half times more likely to be diagnosed with dementia, whereas women with ADHD were over three times more likely, than non-ADHD peers.
More concerning still, persons with ADHD were 5.5 times more likely to be subsequently diagnosed with early onset dementia, as opposed to 2.4 times more likely to be diagnosed with late onset dementia.
On the other hand, the team found no significant difference in rates of dementia between individuals with ADHD who were being treated with stimulant medications and individuals without ADHD. Those with untreated ADHD had three times the rate of dementia. The team nevertheless cautioned, “Due to the underdiagnosis of dementia as well as bidirectional misdiagnosis, this association requires further study before causal inference is plausible.”
Conclusions and Relevance:
This study reinforces existing evidence that adult ADHD is associated with an increased risk of dementia. Notably, the increased risk was not observed in individuals receiving psychostimulant medication, however the mechanism behind this association is not clear.
These findings underscore the importance of reliable ADHD assessment and management in adulthood. They also highlight the need for further study into the link between stimulant medications and the decreased risk of dementia.
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