December 11, 2023

Sex Differences in ADHD Symptoms and Related Cognitive Deficits in Youths

To what extent does sex matter in the expression of ADHD symptoms and associated cognitive deficits among youths with ADHD?

A recently published meta-analysis of 54 studies by a Canadian team of researchers at the University of Quebec at Montreal suggests it makes little to no difference. A meta-analysis of 26 studies with over 5,900 youths found no significant difference in inattention symptoms, and a meta-analysis of 24 studies with over 5,500 youths likewise found no difference in hyperactivity-impulsivity symptoms. Separating out hyperactivity and impulsivity made no difference.

Given these results, it's no surprise that a meta-analysis of 15 studies with over 3,500 youths again found no significant divergence between the sexes for total ADHD symptoms. Parents and teachers differed, however, in their ratings of symptoms. Whereas parents observed no differences, teachers reported boys had slightly more inattention and hyperactive-impulsive behaviors than girls. Turning to cognitive functions, a series of meta-analyses found no significant sex differences for interference control, working memory, and planning scores. But boys performed slightly worse on inhibition and motor response inhibition. While the raw data also showed boys slightly under-performing girls on cognitive flexibility, strong evidence of publication bias made this unreliable.

The team also compared youths with ADHD and youths without ADHD. Both for females and for males, those differences in ADHD symptoms were - as would be expected - extremely large, whether for total symptoms, inattention, or hyperactivity-impulsivity. All cognitive function scores were moderately better for normally developing boys compared with boys with ADHD, and for normally developing girls compared with girls with ADHD. Yet once again, when comparing these effect sizes between girls and boys, there were no significant differences for any of the symptom and cognitive function effects.

"In other words," the authors wrote, "boys and girls with ADHD presented significantly more primary symptoms and executive and attention deficits than did their peers without ADHD, and effect sizes were not significantly different between the sexes." They concluded, "girls with ADHD do not differ from boys with ADHD in many domains of cognitive functioning, and they have significantly more severe difficulties across the executive and attentional functions measured relative to girls without ADHD. This meta-analysis is the first to examine sex differences in cognitive flexibility, working memory, and planning."

Maryanne LoyerCarbonneau, Martin Demers, Marc Bigras, and Marie-Claude Guay, "Meta-Analysis of Sex Differences in ADHD Symptoms and Associated Cognitive Deficits," Journal of Attention Disorders (2020), https://doi.org/10.1177/1087054720923736.

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Meta-analysis Suggests an Adjunct Role for Vitamin D Supplementation for Treating ADHD

Vitamins play important roles in metabolism, immune regulation, and neurodevelopment. Recent studies show that deficiencies in vitamins like D, B6, B12, and folate are common in people with ADHD and ASD (autism spectrum disorder), and are associated with behavioral, cognitive, and brain development issues. 

The Study:

A study team based in China has just performed a systematic search of the peer-reviewed medical literature to perform meta-analyses of clinical trials exploring vitamin interventions in the treatment of ADHD and ASD.  

ADHD trials included participants with an official diagnosis. The primary intervention was vitamin supplements, while other treatments, including medications, remained unchanged or were excluded during the study period. ADHD outcomes included measurable changes in ADHD symptoms using validated rating scales and executive function measures. 

Eligible studies included standard or sham control groups, crossover, parallel, or other clinical trial designs. In crossover studies, only first-phase data were analyzed to prevent carryover effects. 

Ten trials with 852 participants met the standards, but meta-analysis showed no significant results. The outcomes varied widely, suggesting a need to distinguish among vitamins. 

Results:

Of the five trials involving 347 participants that specifically evaluated vitamin D supplementation, results indicated a large effect size improvement in ADHD symptoms and executive function measures. The other five studies did not show any observable improvement. 

Key limitations include: 

  • Vitamin D supplementation studies were not separately assessed. 
  • High heterogeneity persisted in study outcomes, likely due to varying study designs. 
  • Participant numbers were relatively small. 

The team concluded, “This meta-analysis supports the use of vitamin supplementation as a promising adjunctive treatment for ASD and ADHD. Vitamin B showed greater benefits in improving symptoms of ASD, while vitamin D was more effective in managing ADHD-related behaviors. These findings suggest that specific vitamins may target disorder-specific symptoms. Despite limitations such as the lack of trials on other vitamins and limited understanding of underlying mechanisms, vitamin therapy remains a low-cost, accessible option.” 

An important limitation of this work is that the positive results for vitamin D were due to two studies from Iran.  So far, no positive study has emerged from a non-Iranian study.

Interpretation: 

The vitamin D findings are intriguing and could be important if replicated outside of Iran. Since supplementation is already widely recommended to those with limited sunlight exposure, clinicians may want to consider monitoring their patients’ vitamin D intake, especially in the winter months. It should be noted, however, that due to the limitations of this study, the results are by no means conclusive, and vitamin D should not be taken as a stand-alone treatment for ADHD. 

October 10, 2025

Analysis of ADHD Comorbidities and Additional Healthcare Costs

Claims-based real-world data can reveal population-level trends in health among people with neurodevelopmental disorders. This new study examined the prevalence, demographics, and chronic comorbidities of adults and of children and adolescents with ADHD in a large national health plan. It also compared healthcare use and costs between those with and without ADHD. 

A research team in the United States conducted an observational cohort study using claims data from more than 1.9 million adults and nearly 500,000 children and adolescents, comparing individuals diagnosed with ADHD to those without the diagnosis. 

ADHD was diagnosed in 4% of adults and in 5% of children and adolescents. 

Comorbidities By The Numbers: 

Disruptive childhood disorders are behavioral problems marked by ongoing defiance, uncooperativeness, and aggression that affect a child's daily life and relationships. The main types, oppositional defiant disorder (ODD) and conduct disorder (CD), involve persistent anger and argumentativeness in ODD, and more severe actions like aggression, cruelty, and criminal behavior in CD. Without treatment, these common childhood disorders can continue into adulthood and raise the risks of substance use, violence, incarceration, and early death. 

Disruptive childhood disorders were twenty times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and fifteen times more frequent among adults with ADHD. 

Bipolar disorder was twelve times more common among children and adolescents with ADHD than those without ADHD, and seven times more common among adults with ADHD. 

Schizophrenia was eleven times more prevalent among children and adolescents with ADHD than those without ADHD, and three-and-a-half times more common among adults with ADHD. 

Anxiety was nine times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and more than five times more frequent among adults with ADHD. 

Depression was eight times more common among children and adolescents with ADHD than those without ADHD, and more than five times more common among adults with ADHD. 

Suicidal ideation was eight times more prevalent, and suicide attempt seven times more prevalent, among children and adolescents with ADHD than those without ADHD. Both suicidal ideation and suicide attempt were five times more common among adults with ADHD. 

Gender dysphoria was almost six times more frequent among children and adolescents with ADHD than among those without ADHD diagnosis, and five times more frequent among adults with ADHD.  

Eating disorders were over four times more common among children and adolescents with ADHD than those without ADHD, and five times more common among adults with ADHD. 

Substance-related disorders were over six times more prevalent, and alcohol use disorder was six times more prevalent among children and adolescents with ADHD than those without ADHD, and four and three times more prevalent among adults with ADHD. 

Increased Costs of Medical Care:

These comorbidities and ADHD led to higher medical costs. Children and adolescents with ADHD spent $610 more annually on healthcare than those without, while adults with ADHD had $1,684 higher average yearly expenditures than non-ADHD adults. 

The Take-Away:

This large claims-based analysis of a national commercial insurer found ADHD diagnoses in roughly 4% of adults and 5% of children. It documented substantially higher rates of co-occurring behavioral-health conditions and markedly greater healthcare utilization and expenditures among those with ADHD. The authors report increased odds for several co-occurring diagnoses, as well as higher per-member-per-month (PMPM) spending and per-thousand-per-month (PTPM) utilization, largely driven by greater use of behavioral health services. 

Importantly, these results come from cross-sectional, claims data within a commercially insured population: they describe associations, not causal relationships, and may not generalize to uninsured, publicly insured, or otherwise different populations. These findings, therefore, warrant cautious interpretation and highlight the need for longitudinal and more representative studies to clarify drivers of the increased burden and to inform care and policy.

Population Study Finds Strong Association Between Assisted Reproductive Technologies and Offspring ADHD

Taiwanese Nationwide Population Study Finds Strong Association Between Assisted Reproductive Technologies and Offspring ADHD

Background: 

Since the first in vitro fertilization (IVF) in 1978, assisted reproductive technology (ART) has led to over 10 million births worldwide.  

There are four types of embryo transfers, depending on whether they are fresh or frozen, and on their developmental stage. 

Fresh cleavage stage embryos are transferred on day 2 or 3 following fertilization and typically contain four to eight relatively large, undifferentiated cells. Fresh blastocyst embryos are transferred on day 5 or 6 after fertilization. At this point, they have developed over a hundred cells and have differentiated into two types: the inner cell mass, which develops into the fetus, and the outer cell layer, which forms the placenta. 

Globally, more children are now born through assisted reproductive technology using frozen-thawed embryo transfer than fresh embryo transfer.  

Research suggests that ART-conceived offspring may face increased risks of cardiovascular, musculoskeletal, chromosomal, urogenital diseases, and cancers. Might they also be at increased risk for ADHD? 

Study:

Taiwan’s single-payer health insurance covers over 99% of people and records all their healthcare activity. Since 1998, it has kept an ART database for all couples registered for IVF treatment. 

A Taiwanese research team reviewed all records for the five-year period from 2013 through 2017, ultimately analyzing 3,125 live singleton births from fresh cleavage stages, 1,332 from fresh blastocysts, 1,465 from frozen cleavage stages, and 4,708 from frozen blastocysts, alongside 878,643 naturally conceived singleton births. 

The team controlled for the following potential confounders: pregnancy-induced hypertension, chronic hypertension, diabetes mellitus, gestational diabetes mellitus, unhealthy lifestyle, placenta previa, placenta abruption, preterm premature rupture of membrane, and postpartum hemorrhage. 

Results:

With these adjustments, cleavage stage embryo transfers, whether fresh or frozen, were associated with a seven-fold higher rate of ADHD diagnosis in offspring than natural conception. 

Frozen blastocyst embryo transfers were likewise linked to a seven-fold increase in ADHD diagnoses in offspring compared to natural conception. Notably, fresh blastocyst transfers showed a 19-fold increase, likely due to the smaller number of cases in this category. 

The team concluded, “Compared to natural conception, ART is associated with higher risks, particularly for preterm birth, ADHD, and developmental delay.” 

Conclusion: 

This large national cohort suggests that ART-conceived singletons face higher rates of several adverse outcomes, including preterm birth, ADHD, and developmental delay. Clinicians and prospective parents should therefore weigh these potential associations when counseling and planning care, prioritize optimized ART protocols and perinatal management, and ensure early developmental surveillance for ART-conceived children so concerns can be identified and addressed promptly.

It is important to note that the findings also point to the likely contribution of underlying parental infertility in these developmental outcomes. Future research should aim to disentangle parental- versus procedure-related risks to clarify absolute risk magnitudes. As always, associations of this time should not be interpreted as causal due to the inability of observational studies to rule out all possible confounding factors.

October 1, 2025