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July 14, 2025
Serotonin is a key chemical in the body that helps regulate mood, behavior, and also many physical functions such as sleep and digestion. It has also been linked to how ADHD (attention-deficit/hyperactivity disorder) develops in the brain. This study looks at how serotonin may be involved in both the mental health and physical health conditions that often occur alongside ADHD.
It is well-established that ADHD is more than just trouble focusing or staying still. For many, it brings along a host of other physical and mental health challenges. It is very common for those with ADHD to also have other diagnosed disorders. For example, those with ADHD are often also diagnosed with depression, anxiety, or sleep disorders. When these issues overlap, they are called comorbidities.
A new comprehensive review, led by Dr. Stephen V. Faraone and colleagues, delves into how serotonin (5-HT), a major brain chemical, may be at the heart of many of these common comorbidities.
Serotonin is a neurotransmitter most often linked to mood, but its role in regulating the body has much broader implications. It regulates sleep, digestion, metabolism, hormonal balance, and even immune responses. Although ADHD has long been associated with dopamine and norepinephrine dysregulation, this review suggests that serotonin also plays a central role, especially when it comes to comorbid conditions.
This research suggests that serotonin dysregulation could explain the diverse and sometimes puzzling range of symptoms seen in ADHD patients. It supports a more integrative model of ADHD—one that goes beyond the brain’s attention, reward and executive control circuits and considers broader physiological and psychological health.
future research into the role of serotonin could help develop more tailored interventions, especially for patients who don't respond well to stimulant medications. Future studies may focus on serotonin’s role in early ADHD development and how it interacts with environmental and genetic factors.
This study is a strong reminder that ADHD is a complex, multifaceted condition. Differential diagnosis is crucial to properly diagnosing and treating ADHD. Clinicians' understanding of the underlying link between ADHD and its common comorbidities may help future ADHD patients receive the individualized care they need. By shedding light on serotonin’s wide-reaching influence, this study may provide a valuable roadmap for improving how we diagnose and treat those with complex comorbidities in the future.
Faraone SV, Ward CL, Boucher M, Elbekai R, Brunner E. Role of serotonin in psychiatric and somatic comorbidities of attention-deficit/hyperactivity disorder: A systematic literature review. Neurosci Biobehav Rev. 2025 Jul 5:106275. doi: 10.1016/j.neubiorev.2025.106275. Epub ahead of print. PMID: 40623558.
In the general population, most mothers experience mood disturbances right after childbirth, commonly known as postpartum blues, baby blues, or maternity blues. Yet only about one in six develop symptoms with a duration and magnitude that require treatment for depressive disorder, and one in ten for anxiety disorder.
To what extent does ADHD contribute to the risk of such disorders following childbirth? A Swedish study team used the country’s single-payer health insurance database and other national registers to conduct the first nationwide population study to explore this question.
They used the medical birth register to identify all 420,513 women above 15 years of age who gave birth to their first child, and all 352,534 who gave birth to their second child, between 2005 and 2013. They excluded miscarriages. They then looked for diagnoses of depression and/or anxiety disorders up to a year following childbirth.
In the study population, 3,515 mothers had been diagnosed with ADHD, and the other 769,532 had no such diagnosis.
Following childbirth, depression disorders were five times more prevalent among mothers with ADHD than among their non-ADHD peers. Excluding individuals with a prior history of depression made little difference, lowering the prevalence ratio to just under 5. Among women under 25, the prevalence ratio was still above 3, while for those 25 and older it was above 6.
Similarly, anxiety disorders were over five times more prevalent among mothers with ADHD than among their non-ADHD peers. Once again, excluding individuals with a prior history of depression made little difference, lowering the prevalence ratio to just under 5. Among women under 25, the prevalence ratio was still above 3, while for those 25 and older it was above 6.
The team cautioned, “There is a potential risk of surveillance bias as women diagnosed with ADHD are more likely to have repeated visits to psychiatric care and might have an enhanced likelihood of also being diagnosed with depression and anxiety disorders postpartum, compared to women without ADHD.”
Nevertheless, they concluded, “ADHD is an important risk factor for both depression and anxiety disorders in the postpartum period and should be considered in the post- pregnancy maternal care, regardless of sociodemographic factors and the presence of other psychiatric disorders. Parental education prior to conception, psychological surveillance during, and social support after childbirth should be provided to women diagnosed with ADHD.”
Israel has a military draft that applies to males and females alike, except orthodox women and orthodox male seminary(yeshiva) students, who are exempt. Upon turning 17 every Israeli undergoes a medical review, including both a physical and psychiatric assessment, in preparation for the draft. The Draft Board Registry maintains comprehensive health information on all unselected Israelis until they turn 21. The registry also tracks all family members of draft registrants, including full siblings.
An Israeli study team used registry records from 1998 through2014 to obtain data for a total of over a million individuals (1,085,388). Because of the exemption for orthodox women, 59% were male.
The team identified 903,690 full siblings in the study population (58% males), including 166,359 male-male sibling pairs, 104,494 female-female sibling pairs, and 197,571 opposite-sex sibling pairs.
Next, the team identified all cases in the study population with a diagnosis of a psychiatric disorder, low IQ (≥2 standard deviations below the population mean), Type-1 diabetes, hernia, or hematological malignancies. It matched each case with ten age- and sex-matched controls selected at random from the study population. Then, for each case and case-matched controls, it identified all siblings.
There were 3,272 cases receiving treatment for ADHD, 2,128 with autistic spectrum disorder, 9,572 with severe/profound intellectual disability, 7,902 with psychotic disorders, 9,704 with mood disorders, 10,606with anxiety disorders, 24,815 with personality disorders, 791 with substance abuse disorders, 31,186 with low IQ, 2,770 with Type-1 diabetes, 30,199 with a hernia, and 931 with hematological malignancies.
Draftees with ADHD were five and a half times more likely to have a sibling with ADHD than controls.
There were no significant associations between ADHD and any of the somatic disorders - Type-1 diabetes, hernia, or hematological malignancies - nor between ADHD and low IQ.
There were also no significant associations between ADHD and autism spectrum disorder, severe/profound intellectual disability, mood disorders, and substance use disorders.
On the other hand, draftees with ADHD were more than 40% more likely to have siblings with anxiety or personality disorders than controls.
Surprisingly, draftees with ADHD were less than half as likely to have siblings with psychotic disorders than controls.
There were some limitations. The psychiatric classification system used by the Israeli military did not permit assessing the risk of bipolar disorder and depression separately. That meant having to use a broader category of mood disorders, including both disorders. In addition, the military diagnostic system does not allow diagnosis of comorbid psychiatric disorders in the same individual, instead of assigning only the most severe diagnosis.
Although there has been much research documenting that ADHD adults are at risk for other psychiatric and substance use disorders, relatively little is known about whether ADHD puts adults at risk specifically for somatic medical disorders.
Given that people with ADHD tend toward being disorganized and inattentive, and that they tend to favor short-term over long-term rewards, it seems logical that they should be at higher risk for adverse medical outcomes. But what does the data say?
In a systematic review of the literature, Instances and colleagues have provided a thorough overview of this issue. Although they found 126 studies, most were small and were of "modest quality". Thus, their results must be considered to be suggestive, not definitive for most of the somatic conditions they studied.
Also, they excluded articles about traumatic injuries because the association between ADHD and such injuries is well established. Using qualitative review methods, they classified associations as being a) well-established; b) tentative, or c) lacking sufficient data.
Only three conditions met their criteria for being a well-established association: asthma, sleep disorders, and obesity.
They found tentative evidence implicating ADHD as a risk factor for three conditions: migraine headaches, celiac disease, and diseases of the circulatory system.
These data are intriguing, but cannot tell us why ADHD people are at increased risk for somatic conditions. One possibility is that suffering from ADHD symptoms can lead to an unhealthy lifestyle, which leads to increased medical risk. Another possibility is that the biological systems that are dysregulated in ADHD are also dysregulated in some medical disorders. For example, we know that there is some overlap between the genes that increase the risk for ADHD and those that increase the risk for obesity. We also know that the dopamine system has been implicated in both disorders.
Instances and colleagues also point out that some medical conditions might lead to symptoms that mimic ADHD. They give sleep-disordered breathing as an example of a condition that can lead to the symptom of inattention.
But this seems to be the exception, not the rule. Other medical conditions co-occurring with ADHD seem to be true comorbidities, rather than the case of one disorder causing the other. Thus, primary care clinicians should be alert to the fact that many of their patients with obesity, asthma, or sleep disorders might also have ADHD.
By screening such patients for ADHD and treating that disorder, you may improve their medical outcomes indirectly via increased compliance with your treatment regime and an improvement in health behaviors. We don't yet have data to confirm these latter ideas, as the relevant studies have not yet been done.
Background:
Traditional measures of obesity, like body mass index (BMI) and waist circumference, have been linked to ADHD risk — but they aren’t great at capturing where fat is actually stored in the body. A newer index called relative fat mass (RFM), which combines height and waist circumference, does a better job of estimating overall body fat and predicting metabolic risks like heart disease and metabolic syndrome. Because those conditions share some underlying biological mechanisms with ADHD, researchers wondered whether RFM might also help explain the relationship between obesity and ADHD — particularly in children.
That question is complicated by the fact that ADHD doesn't look the same in boys and girls. Boys tend to display more hyperactive and impulsive behavior, making their ADHD easier to spot. Girls more often show inattention, which is quieter and frequently goes undiagnosed.
The Study:
A new study set out to test whether RFM is associated with ADHD in children, and whether that association differs between sexes. Using data from the National Health and Nutrition Examination Survey (NHANES) collected between 1999 and 2004, the researchers narrowed a large initial pool of over 31,000 participants down to 5,089 children and adolescents aged 6 to 14 who had complete data on height, waist circumference, ADHD screening, and other relevant variables.
After adjusting for age, race/ethnicity, Poverty-Income Ratio, maternal age at delivery, maternal smoking during pregnancy, health insurance coverage, and birth weight, the results revealed a striking split along sex lines.
In boys, higher RFM was associated with lower odds of ADHD. Compared to boys in the lowest fat-mass quartile, those in the second quartile had about 10% lower odds of ADHD, rising to over 30% lower in the third quartile and nearly 40% lower in the highest. In girls, the pattern reversed entirely. While girls in the second quartile showed similar odds to those with the lowest RFM, girls in the third and fourth quartiles had 60% to 70% greater odds of ADHD.
Conclusion & Why This Matters:
In recent years, the relationship between obesity and ADHD has become an increasingly important focus in pediatric neurodevelopmental research. Studies have reported higher rates of ADHD symptoms among children and adolescents with obesity compared with their non-obese peers, and difficulties with peer relationships have also been linked to increased obesity risk (Sönmez et al., 2019). From a neurobiological standpoint, both conditions may involve shared underlying mechanisms, particularly dysfunction in dopaminergic pathways.
The authors concluded that higher body fat levels appear to lower ADHD risk in boys while raising it in girls. This finding highlights why sex-specific analysis matters in ADHD research. The underlying biological reasons for this divergence, however, remain an open question and open the door for future research.
While ADHD is a developmental disorder, shaped by biology and genetics, growing evidence shows that it is also influenced by the social and environmental conditions in which children grow up. Research on the social determinants of health emphasizes that development is shaped not only by biology but also by factors such as family income, access to healthcare, neighborhood safety, and material stability. These factors can affect both how developmental challenges appear and whether they are recognized and diagnosed.
Children facing socioeconomic disadvantage consistently show higher risks of developmental and behavioral difficulties. Chronic stress linked to poverty – including financial strain, food insecurity, and limited access to resources – has been associated with problems in attention, emotional regulation, and daily functioning. Children from lower-income families also tend to experience more severe ADHD symptoms and face greater barriers to ongoing care.
Neighborhood conditions matter as well. Unsafe environments can limit opportunities for play and social interaction while increasing caregiver stress, all of which may influence children’s behavior and development. Material hardships, such as food insecurity, can further undermine stability at home.
The Study:
The study analyzed six years of data from the National Survey of Children’s Health (2018–2023), covering more than 205,000 U.S. children aged 3 to 17. After accounting for age, sex, race and ethnicity, region, family structure, survey year, and other social factors, the researchers found a strong income gradient in ADHD prevalence. Compared with children in households earning at least four times the federal poverty level, those in households earning two to four times that level had 28 percent higher odds of ADHD. Odds rose to 70 percent higher in households earning one to two times the poverty level, and more than doubled among children living below the poverty line.
Parental education showed a similar pattern. Compared with children whose parents had completed college, ADHD odds were 20 percent higher among those whose parents had some college education, 40 percent higher among those whose parents had only a high school education, and 80 percent higher among those whose parents had not finished high school.
Children living in unsafe neighborhoods had nearly twice the odds of ADHD compared with those in safe neighborhoods, and food insecurity was also linked to almost double the odds.
By contrast, race and ethnicity alone were associated with much smaller differences. Compared with non-Hispanic White children, children in non-Hispanic Black households had an 18 percent higher likelihood of ADHD, while children in Hispanic households had a 25 percent lower likelihood. No substantial differences were observed for children from other or multiracial households.
Conclusion and Takeaway:
The study team concluded, “Children living in lower-income households, experiencing food insecurity, and residing in unsafe neighborhoods consistently showed higher prevalence and higher adjusted odds of both conditions. … Overall, these findings reinforce the need to view neurodevelopmental disorders within a broader social and structural framework.”
It should be noted that this study is not aiming to name social factors as direct causes of ADHD. Rather, it points to socioeconomic disparities as contributing to the way ADHD develops and how it is treated. This type of research, as well as acknowledging barriers to care, is crucial for clinicians, counselors, teachers, etc., to consider when working with youth with ADHD.
Counting umbilical cord vessels is standard in prenatal ultrasounds and confirmed at birth. Single umbilical artery (SUA) occurs in about 1 in 200 cases, with roughly 10% associated with anomalies, including central nervous system defects. Isolated SUA (iSUA) means one artery is missing without other structural issues.
Research on SUA, especially isolated iSUA, and childhood neurodevelopmental disorders (NDD) is limited and inconclusive. iSUA is linked to preterm birth and small-for-gestational age (SGA), both of which are NDD risk factors.
This Norwegian nationwide population study aimed to assess NDD risk in children with iSUA at birth, the influence of sex, and how preterm birth and SGA mediate this relationship.
The nation’s universal single-payer health insurance and comprehensive population registries made it possible to analyze all 858,397 single births occurring from 1999 to 2013, with follow-up continuing through 2019. Among these cases, 3,532 involved iSUA.
After adjusting for confounders such as parental age, education, and maternal health factors, no overall link was found between iSUA and later ADHD diagnosis. However, females with iSUA had about a 40% higher risk of subsequent ADHD compared to those without iSUA, even after adjustment.
The authors concluded, “The present study indicates that iSUA is weakly associated with ID [intellectual disability] and ADHD, and these associations are influenced by sex. This association is mediated negligibly through preterm birth and SGA. The associations were not clinically significant, and the absence of associations of iSUA with other NDD is reassuring. This finding can be useful in the counseling of expectant parents of fetuses diagnosed with iSUA.”
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