June 30, 2021
All Swedish residents have their health records tracked through unique personal identity numbers. That makes it possible to identify psychiatric and medical disorders with great accuracy across an entire population, in this case encompassing more than five and a half million adults aged 18 to 64. A subgroup of more than 1.6 million persons between the ages of 50 and 64 enabled a separate examination of disorders in older adults.
Slightly over one percent of the entire population (about 61,000) was diagnosed with ADHD at some point as an adult. Individuals with ADHD were nine times as likely to suffer from depression as were adults not diagnosed with ADHD. They were also more than nine times as likely to suffer from anxiety or a substance use disorder, and twenty times as likely to be diagnosed with bipolar disorder. These findings are very consistent with reports from clinical samples in the USA and Europe.
Adults with ADHD also had elevated levels of metabolic disorders, being almost twice as likely to have high blood pressure, and more than twice as likely to have type 2 diabetes. Persons with ADHD but without psychiatric comorbidities were also almost twice as likely to have high blood pressure, and more than twice as likely to have type2 diabetes.
Similar patterns were found in men and women with ADHD, although comorbid depression, bipolar disorder, and anxiety were moderately more prevalent in females than in males, whereas substance use disorder, type 2 diabetes, and hypertension were more prevalent in males than in females.
ADHD was less than a third as prevalent in the over-50 population as in the general adult population. Nevertheless, individuals in this older group with ADHD were twelve times as likely to suffer from depression, anxiety, or substance use disorders, and more than 23 times as likely to be diagnosed with bipolar disorder as their non-ADHD peers. They were also 63% more likely to have high blood pressure, and 72% more likely to have type 2 diabetes.
The authors noted, "Although the mechanisms underlying these associations are not well understood, we know from both epidemiologic and molecular genetic studies that a shared genetic predisposition might account for the coexistence of two or more psychiatric conditions. In addition, individuals with ADHD may experience increased difficulties as the demands of life increase, which may contribute to the development of depression and anxiety." As for associations with hypertension and type 2 diabetes, these "might reflect health risk behaviors among adult patients with comorbid ADHD in addition to a shared biological substrate. As others have noted, inattention, disinhibition, and disorganization associated with ADHD could make it difficult for patients to adhere to treatment regimens for metabolic disorders." They concluded that "Clinicians should remain vigilant for a wide range of psychiatric and metabolic problems in ADHD affected adults of all ages and both sexes."
Qi Chen, Catharina A. Hartman, Jan Haavik, Jaanus Harro, Kari Klungsøyr, TorArne Hegvik, Rob Wanders, Cæcilie Ottosen, Søren Dalsgaard, Stephen V. Faraone, Henrik Larsson, “Common psychiatric and metabolic comorbidity of adult attention-deficit/hyperactivity disorder: A population-based cross-sectional study,” PLoSONE (2018), 13(9): e0204516. https://doi.org/10.1371/journal.pone.0204516.
Background
ADHD (Attention-Deficit/Hyperactivity Disorder) is one of the most studied neurodevelopmental conditions, with many clinical trials evaluating the effectiveness and safety of various medications. These trials, known as randomized controlled trials (RCTs), are considered the gold standard for assessing treatments. However, strict eligibility criteria often exclude many real-world patients, raising questions about whether the findings from these trials apply to everyday clinical settings.
Our latest study sheds light on this issue, revealing just how many individuals with ADHD might be excluded from RCTs and the impact this exclusion has on their treatment outcomes.
Method
Researchers used Swedish national registries to analyze data from 189,699 individuals diagnosed with ADHD who started medication between 2007 and 2019. They applied exclusion criteria from 164 international RCTs to identify who would have been considered ineligible for these trials in order to determine the proportion of individuals with ADHD who would not meet the eligibility criteria for RCTs.
Key Findings
Many Patients Are Ineligible for Clinical Trials:
Ineligible Patients Face Unique Challenges:
Higher Risk of Adverse Outcomes:
What This Means
These findings highlight a major gap between the controlled environments of clinical trials and the realities faced by individuals with ADHD in everyday life. While RCTs provide valuable insights, their restrictive criteria often exclude patients with more complex health profiles or co-existing conditions. This limits the generalisability of trial results, meaning that treatment guidelines based solely on RCTs may not fully address the needs of all patients.
Conclusion
This study demonstrated that a significant proportion of individuals with ADHD, particularly adults, do not meet the eligibility criteria for standard RCTs. These results emphasize the importance of bridging the gap between research settings and real-world applications. By recognizing and addressing the limitations of RCTs, we can work towards more equitable and effective ADHD treatment strategies for everyone.
Background:
Our understanding of Attention-deficit/hyperactivity disorder (ADHD) has grown and evolved considerably since it first appeared in the DSM-II as “Hyperkinetic Reaction of Childhood.” This study aimed to find the disorder’s placement within the modern psychopathology classification systems like the Hierarchical Taxonomy Of Psychopathology (HiTOP).
The HiTOP model aims to address limitations of traditional classification systems for mental illness, such as the DSM-5 and ICD-10, by organizing psychopathology according to evidence from research on observable patterns of mental health problems.. Is ADHD best categorized under externalizing conditions, neurodevelopmental disorders, or something else entirely? A recent study by Zheyue Peng, Kasey Stanton, Beatriz Dominguez-Alvarez, and Ashley L. Watts takes a closer look at this question using a symptom-focused approach.
The Study:
Traditionally, ADHD has been associated with externalizing behaviors, such as impulsivity and hyperactivity, or with neurodevelopmental traits, like cognitive delays. However, this study challenges the idea of placing ADHD into a single category. Instead, it maps ADHD symptoms across three major psychopathology spectra: externalizing, neurodevelopmental, and internalizing.
The findings reveal that ADHD symptoms don’t fit neatly into one box. For example, symptoms like impulsivity, poor school performance, and low perseverance were strongly associated with externalizing behaviors. On the other hand, cognitive disengagement (e.g., daydreaming, blank staring) and immaturity were closely linked to neurodevelopmental challenges. Interestingly, cognitive disengagement also showed ties to internalizing symptoms, such as anxiety or depression.
This research underscores the complexity of ADHD. Rather than treating ADHD as a single, unitary construct, the study advocates for a symptom-based approach to better understand and treat individuals. By acknowledging that ADHD symptoms relate to multiple psychopathology spectra, clinicians and researchers can move toward more nuanced classification systems and targeted interventions.
Conclusion:
Ultimately, this study highlights the need for modern systems to move beyond rigid categories and adopt a more flexible, symptom-focused framework for understanding ADHD’s place in psychopathology.
Exposure to heavy metals like lead, arsenic, mercury, cadmium, and manganese is known to harm developing nervous systems. However, past studies on whether heavy metals specifically increase the risk of ADHD have shown mixed results.
A research team from China (Gu et al., 2024) reviewed medical studies and conducted meta-analyses to better understand this issue.
The team included studies on children and teens, focusing on cohort studies, case-control studies, and cross-sectional studies. They only used articles written in English and required validated biomonitoring (like blood tests) to measure heavy metal exposure. ADHD diagnoses had to come from clinical evaluations.
To be included, studies had to report effect sizes such as odds ratios and relative risks with confidence intervals. The team focused on comparisons between groups with high, low, or no exposure, which made it harder to analyze dose-response relationships.
They also evaluated the quality of each study. All cohort studies were rated high-quality. Of the 15 case-control studies, 6 were high-quality, and 9 were moderate-quality. Among cross-sectional studies, only 2 were high-quality, and the rest were moderate-quality.
There was no evidence linking ADHD to other heavy metals like arsenic, mercury, cadmium, or manganese. Both meta-analyses suggest that lead exposure is associated with the risk for ADHD. However, because these studies cannot rule out other explanations, one cannot conclude that lead exposure causes ADHD. For example, other work shows that people with ADHD are likely to have lower incomes than those without ADHD.
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