Abstract
To the Editor:
Your journal has published contradictory information related to ADHD symptomatology. Vogel et al. (2019) provided the first evidence demonstrating seasonal variability in the severity of symptoms of ADHD. The authors analyzed ADHD symptoms among 5,303 respondents participating in the Netherlands Mental Health Survey and Incidence Study–2. Total ADHD and inattention subscale scores were significantly higher among participants who were assessed in spring/summer versus the autumn period. Consistently, hyperactivity subscale scores were also higher in the spring.
Although, earlier in your journal, Arns, Swanson, and Arnold (2018) discussed their ecological findings showing a lower ADHD prevalence in geographical areas with high solar intensity (SI), which Arns et al. (2018) say is the likely unmeasured confounder responsible for the association between altitude and lower ADHD prevalence (Huber et al., 2018). Although controlling for altitude in their original analysis with SI and ADHD prevalence did yield only trend level of significance for SI in 2003 (p > .05), suggesting an interdependence between SI and altitude in the lower ADHD prevalence. Yet, SI exhibits seasonal variation, with greater intensity during summer months (U.S. Department of Energy, 2018). So, these reports reveal a lingering inconsistency in your journal on the role of environmental factors in ADHD that requires clarification.
Therefore, the purpose of the letter is to attempt to resolve this inconsistency. Increasing environmental emissions of N2O have been implicated in the etiology of neurodevelopmental disorders (Fluegge & Fluegge, 2017 and complete Citation List—My Bibliography at PubMed: https://www.ncbi.nlm.nih.gov/sites/myncbi/1r5h3UjOlyj5q/bibliography/51230181/public/?sort=date&direction=descending). Although N2O is classified by the World Health Organization as an important modern health medicine, it must be acknowledged that the compound exists as a greenhouse gas, with an estimated global warming potential nearly 300 times that of carbon dioxide. Also of concern, N2O is a widespread gaseous air pollutant that is derived from anthropogenic nitrogen use in agriculture (73% of total emissions) as well as mobile and stationary combustion-related processes from energy and transportation sources (19% of total emissions).
Prior analyses have linked statewide anthropogenic nitrogen use in agriculture to an increased risk of hospitalization for an all-listed ADHD diagnosis, representing a severely impaired phenotype (Fluegge & Fluegge, 2017). Several pathophysiological mechanisms by which trace environmental exposure to N2O may increase risk for ADHD include N-methyl-D-aspartate receptor antagonism, kappa opioidergic stimulation, and α7 nicotinic acetylcholine receptor inhibition (Fluegge, 2016). Clinical evidence suggests that trace N2O exposure may induce impairments in continuous attention (Bruce, Bach, & Arbit, 1974; Fried, Garrioch, Tiplady, & Wildsmith, 1995). Moreover, marked reductions in striatal dopaminergic transmission, a key pharmacological target in ADHD psychostimulant therapy (Volkow et al., 2012), have been shown in mice chronically exposed to trace levels of N2O (Abdul-Kareem, Sharma, & Drown, 1991). It can, therefore, be concluded that trace N2O exposure contributes to both the neurobiological dimension of ADHD and to the disorder’s clinical manifestations.
Importantly, environmental N2O emissions reflect the seasonal application of anthropogenic nitrogen in agriculture, with spring/summer showing the greatest application and emission rates (Bremner, Robbins, & Blackmer, 1980; Skiba et al., 2012). Moreover, the antinociceptive effects of N2O are significantly reduced at higher altitudes (James, Manson, & Dennett, 1982), while lower altitudes may allow higher N2O fluxes, creating emission hotspots (Yanai et al., 2003). Therefore, consideration of environmental N2O in ADHD etiology (Fluegge, 2016; Fluegge & Fluegge, 2017) could help to explain both the seasonal variation in ADHD symptom severity and the lower prevalence at higher altitudes with greater SI. We would urge researchers to begin systematic quantitative assessments of trace environmental N2O emissions to understand whether such emissions play a casual factor in ADHD pathogenesis. Unfortunately, we are not aware of any such initiatives currently underway.