Attention deficit hyperactive disorder(ADHD) is a neuropsychiatric disorder characterized by inattention, impulsiveness, and hyperactivity.1,2 The condition is commonly treated with stimulant therapy (methylphenidates or amphetamines in various forms). 3 Stimulants tend to increase dopamine activity in the brain, and it is speculated that this may help with ADHD symptoms. 4 In cases where stimulants are not well tolerated, nonstimulants, such as atomoxetine, guanfacine, and clonidine, are often recommended.5
Despite decades of research, there continues to be a debate on the symptoms, etiology, and progression of ADHD. Symptoms in adult ADHD, for instance, tend to be distinct from those generally depicted in children. Research has shown that many symptoms in adults with ADHD might be related to impairment in social cognition domains. Inattention in adults might be displayed through disorganization, forgetfulness, and difficulty staying focused on tasks. The hyperactive and impulsive symptoms may manifest themselves through distinct behaviours. Verbal impulsivity, difficulty making decisions, and sometimes not thinking before proceeding with action might be examples of such behaviours in adults. This paper seeks to shed some clarity on this vaguely understood disorder. More specifically, it discusses the possible etiology and progression of ADHD into adulthood and a few of its comorbid conditions. Further, a significant parameter that needs to be addressed in treating ADHD patients will be discussed.
Mothers’ Thyroid Function and Children’s Development of ADHD
Recent longitudinal study results following 329,157 children from birth until age 17 reveal that hypothyroidism in pregnant mothers is linked to ADHD in their children. 7 Children’s medical records, the mother’s age during pregnancy, race, and household incomes were considered to further account for confounding variables. Children were also evaluated for ADHD using the same criteria to prevent inconsistencies in diagnosis. Children whose mothers were diagnosed with hypothyroidism before or during the first three months of pregnancy were 24% more likely to have ADHD. The association between maternal hypothyroidism and incidences of ADHD in children varied with gestational age at delivery, child sex, and race or ethnicity. Boys born to hypothyroid mothers (IRD = 1.84 and aHR = 1.26; 95% CI: 1.14–1.40), for instance, were four times more vulnerable to the development of ADHD than girls (IRD = 0.48 and aHR = 1.19; 95% CI: 1.01—1.40) whose mothers had hypothyroidism.8
Progression of ADHD into Adulthood ADHD
Unfortunately, most children diagnosed with ADHD do not outgrow the condition as widely as once thought; it continues to manifest itself in adulthood in various ways. The condition tends to continue through a lifetime with intermittent periods of remission. In the Multimodal Treatment Study of ADHD, children with ADHD (n = 558) underwent eight assessments over follow-ups occurring 2 to 16 years after the baseline. Participants were categorized as fully remitted, partially remitted, or experiencing persistent ADHD symptoms. Longitudinal patterns of remission and persistence were recognized based on a parent, teacher, and self-reports of ADHD symptoms, treatment utilization, impairment, substance use, and other mental disorders. Only 10% of children outgrew the disorder entirely (compared to the previous common assumption that 50% of children with ADHD outgrow the condition). The rest continued to experience residual symptoms into young adulthood. 9 The disorder, however, does not emerge until adulthood for some people. In an environmental risk (e‑risk) longitudinal twin study of more than 2,200 participants, symptoms of childhood ADHD were assessed at ages 5, 7, 10, and 12 through mother and teacher reports. The participants were later interviewed at age 18 to evaluate for ADHD symptoms, any associated impairments, and the existence of other mental health disorders. Results revealed that many adults with ADHD did not have the condition in childhood.10
Adult ADHD and its Cooccurring Conditions
Regardless of when the ADHD symptoms were first observed, adults with ADHD are at a higher risk of various conditions, including nervous, respiratory, musculoskeletal, and metabolic diseases. Results from a longitudinal study examining the risk of 35 different physical conditions in over 4 million individuals with ADHD compared to those without it (and in siblings of individuals with ADHD compared to siblings of those without the condition) revealed that those with ADHD had a statistically significant increased risk of most studied physical conditions. 11 ADHD is strongly associated with nervous system conditions and musculoskeletal, respiratory, and metabolic diseases. Alcohol-related liver disease, sleep disorders, chronic obstructive pulmonary disease (COPD), epilepsy, fatty liver disease, and obesity were also among the diagnoses most strongly associated with ADHD. ADHD was also linked to a slightly higher risk of Parkinson’s disease, cardiovascular conditions, and dementia.12
Is ADHD a Sleep Problem?
A research proposes a new theory that ADHD may be associated with a lack of regular circadian function. 13,14,15 Recent data has shown that single-nucleotide polymorphism in circadian genes is associated with ADHD symptoms, increased evening orientation, and sleep problems. Those who have ADHD tend to exhibit greater alertness in the evening. Hence, morning bright-light therapy has been proven effective for realigning circadian physiology toward mornings, reducing sleep disturbances, and improving ADHD symptoms. 16 Research has also demonstrated that a lower prevalence of ADHD is present in regions with high sunlight intensity, further suggesting that high sunlight intensity during the daytime may exert a preventative effect on ADHD. 17 Data from a self-reported online survey (n = 494) indicates that around 70% of adults with ADHD exhibit photophobia. This oversensitivity of the eyes to light has led many people with ADHD to wear sunglasses for extended periods during the day, further disrupting the regular functioning of the circadian rhythm. The photophobia may also alter the eye’s dopamine and melatonin production systems, further reinforcing the problems associated with a “circadian shift.”18
Is the Link Between Maternal Thyroid Function and Children’s ADHD Development Mediated through Sleep and Circadian Rhythm?
Further research is warranted to investigate the mediation of the link between maternal thyroid function during early pregnancy and the development of ADHD in children. As mentioned above, ADHD may be associated with circadian function disturbances. 19,20,21 A literature review examining the associations between thyroid disease and sleep disorders has indicated that thyroid conditions have clinical overlaps with sleep conditions such as insomnia. 22 Preliminary research has also shown that there might be an interconnection between circadian clocks and thyroid function. 23 In future work, investigating the role of circadian rhythm alterations as a possible mediator of the link between maternal thyroid function during early pregnancy and the development of ADHD in children might prove crucial.
Is the Link between Adult ADHD and Its Cooccurring Conditions Also Mediated through Sleep and Circadian Rhythm?
Results from a systematic review examining the associations between sleep timing, sleep consistency/regularity, and health outcomes in adults aged 18 years and older suggest that later sleep timing and greater sleep variability are generally associated with adverse health outcomes. The review included results from four electronic databases searched in December 2018 for articles published in the previous 10 years. A total of 41 articles, including 92,340 unique participants from 14 countries, were included in the review. 24 Given the possible link between ADHD and interruption in circadian rhythm, and the effects of sleep regulation on health outcomes, this paper speculates that the negative comorbid health outcomes seen in patients with ADHD might also be mediated through interruptions in sleep and circadian rhythm. This assumption might be addressed in future studies.
In conclusion, there seems to be an association between interruption in circadian function and ADHD. It is well-known that chronic late sleep and sleep debt, as seen in patients with ADHD, are associated with obesity, diabetes, cardiovascular disease, and cancer. This cascade of adverse health consequences may partly explain the comorbid conditions of adult ADHD. Evidence shows that thyroid disorders also have a unique relationship with sleep dysfunction. Exploring the possible alteration of the circadian rhythms in hypothyroid mothers and ADHD children may aid further investigation. Naturopathic practitioners may use gentle approaches to help reset the circadian rhythm when treating ADHD patients, and also help individuals with their sleep.
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