The Association between ADHD and Environmental Chemicals—A Scoping Review
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Substances with Moderate to High Evidence of Association with ADHD
3.1.1. Lead (Pb)
3.1.2. Phthalates
3.1.3. Bisphenol A
Substance | Study | Countries | n, Setting, Target Group | Main Findings and Conclusions |
---|---|---|---|---|
Lead (Pb) | Donzelli et al. (2019). The Association between lead and Attention-Deficit/Hyperactivity Disorder: A Systematic Review. Int J Environ Res Public Health. 2019;16:382 [17] | Mexico China USA South Korea Germany Spain Belgium Taiwan Turkey | n of studies: 17 n of participants: 8940 (range 117–2195) Setting: 2 cross-sectional, 5 birth cohort, 10 case–control Target group: exposure assessment to lead performed during pregnancy and early childhood | 12 studies showed positive associations between lead exposure and ADHD whereas the remaining 5 studies found no association. The authors conclude there is an association between lead and ADHD and even low levels of lead raise the risk. |
Pb | Nilsen and Tulve (2020). A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD. Environ Res. 2020;180:108884 [18] | Canada South Korea China Mexico Romania USA India United Arab Emirates | n of studies: 13 on lead n of participants: 25,253 1, 17,158 2 Setting: observational Target group: infants, children, and adolescents (for lead, ages 3 to 12 included) | The overall OR for Pb exposure being associated with an ADHD diagnosis was 3.39 (90% CI 2.66–4.12, p < 0.001). The OR for specific ADHD diagnoses was 4.06 (2.89–5.23, p < 0.001). The certainty of evidence in ADHD-specific and all-symptom meta-analyses was determined to be ‘moderate’. |
Phthalates | Praveena et al. (2020) Phthalates exposure and attention-deficit/hyperactivity disorder in children: a systematic review of epidemiological literature. Environ Sci Pollut Res Int. 2020;27(36):44757–44770. [26] | Canada South Korea USA Central Taiwan Japan Belgium Norway China | n of studies: 16 n of participants: 7019 (range 122–1318) Setting: cross-sectional, cohort, case–control Target group: infants, children, adolescents (5 weeks to 16 years) | 14 studies found an association between phthalate exposure and ADHD. One study found no significant association between phthalate concentration and ADHD at age five. The remaining study found sex-specific associations with behavior scores among children. The authors conclude that despite the observed associations, due to study limitations, it is difficult to produce definite conclusions. |
Bisphenol A (BPA) | Rochester et al. (2018). Prenatal exposure to bisphenol A and hyperactivity in children: a systematic review and meta-analysis. Environ Int. 2018;114:343–356 [28] | Spain USA | n of studies: 3 human studies n of participants: 1151 (range 237–657) Setting: prospective/longitudinal birth cohort Target group: exposure during gestation or childhood | The systematic review among human studies found that early BPA exposure is associated with a presumed hazard of hyperactivity in humans. All three human studies showed significant effects of BPA on hyperactivity. |
Phthalates/BPA 3 | Nilsen and Tulve (2020). A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD. Environ Res. 2020;180:108884 [18] | USA (two studies on BPA) China (BPA) China (Ph) South Korea (Ph) | n of studies: 5 studies on phthalates/plasticizers (bisphenol A also included in this category) n of participants: 21,594 Setting: observational Target group: infants, children and adolescents (ages 6 to 18), only studies examining exposure after birth included | OR for ADHD diagnosis associated with phthalates/plasticizers in both sexes was 3.31 (2.59–4.02, p < 0.0001). The level of certainty was ‘moderate’, and these results indicate an increase in ADHD with phthalates/plasticizers exposure. |
3.2. Substances with Limited Evidence of Association with ADHD
3.2.1. Polycyclic Aromatic Hydrocarbons (PAHs)
3.2.2. Flame Retardants
3.2.3. Mercury
3.2.4. Pesticides
3.3. Substances with Low Evidence of Association with ADHD
Cadmium and Per- and Polyfluoroalkyl Substances
4. Discussion
5. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Substance | Study | Countries | n, Setting, Target Group | Main Findings and Conclusions |
---|---|---|---|---|
Polycyclic aromatic hydrocarbons (PAH) | Rezaei Kalantary et al. (2020). Association between exposure to polycyclic aromatic hydrocarbons and attention deficit hyperactivity disorder in children: a systematic review and meta-analysis. Environ Sci Pollut Res Int. 2020;27:11531–11540 [31] | Spain USA | n of studies: 6 in the systematic review and 5 in the meta-analysis n of participants: 2799 (range 242–1257) Setting: cohort and cross-sectional studies Target group: children | There was no significant association between PAH exposure and ADHD for children when all studies were combined (overall odds ratio = 1.99, 95% CI = 0.96–4.11) with low heterogeneity (I2 = 28.73%; p < 0.001). However, the authors concluded that PAH have a vital role in child ADHD. |
PAH | Aghaei et al. (2019). Association between ambient gaseous and particulate air pollutants and attention deficit hyperactivity disorder (ADHD) in children; a systematic review. Environ Res. 2019;173:135–156 [32] | Spain USA | n of studies: 7 n of participants: 2944 (range 215–1257) Setting: cohort and cross-sectional studies Target group: children | Eleven associations were investigated in seven studies related to PAH in which five significant associations were observed. On the other hand, no associations were found in six investigations. Although limited evidence of detrimental effects of PAH on ADHD was found in this review, moderate-quality studies in terms of exposure assessment showed positive associations. |
Flame retardants (FR) | Lam et al. (2017). Developmental PBDE Exposure and IQ/ADHD in Childhood: A Systematic Review and Meta-analysis. Environ Health Perspect. 2017;125(8):086001 [33]. | USA Spain Netherlands | n of studies: 9 n of participants: 2033 1 (range 43–622) Setting: cohort and cross-sectional studies Target group: mother–child pairs | In this systematic review developmental exposure to polybrominated diphenyl ethers (PBDEs) and intelligence or ADHD and attention-related behavioral conditions in humans were reviewed. The body of evidence was of moderate quality for ADHD with “limited” evidence for an association with PBDEs. |
FR | Doherty (2019). Organophosphate Esters: Are These Flame Retardants and Plasticizers Affecting Children’s Health? Curr Environ Health Rep. 2019;6:201–213 [34] | USA | n of studies: 2 n of participants: 488 1 (range 199–282) Setting: prospective pregnancy cohorts Target group: children | Greater hyperactivity was associated with organophosphate ester metabolites. However, the available studies have limitations. More evidence needed. |
Mercury (Hg) | Yoshimasu et al. (2014). A meta-analysis of the evidence on the impact of prenatal and early infancy exposures to mercury on autism and attention deficit/hyperactivity disorder in the childhood. Neurotoxicology. 2014;44:121–131 [35]. | Canada USA | n of studies: 2 studies with 3 data sets for methylmercury with relevant exposure periods n of participants: 1067 (range 279–788) Setting: cohort study Target group: children | Environmental methylmercury exposure showed moderate adverse effects on ADHD (OR 1.60, 95% CI 1.10–2.33). With a low number of studies, the authors advise cautious interpretation of results. |
Hg | Nilsen and Tulve (2020). A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD. Environ Res. 2020;180:108884 [18] | Canada South Korea United Arab Emirates | n of studies: 3 studies on mercury n of participants: 2139 Setting: observational Target group: age range 5–15 years | The OR for Hg exposure and all ADHD outcomes was 2.68 (2.16–3.19, p < 0.0001). The authors conclude that despite significant results, the number of studies is small, and a relationship cannot be proven. |
Pesticides | Nilsen and Tulve (2020). A systematic review and meta-analysis examining the interrelationships between chemical and non-chemical stressors and inherent characteristics in children with ADHD. Environ Res. 2020;180:108884 [18] | USATaiwan | n of studies: 6 n of participants: 6440 (range 117–2546) Setting: cross-sectional and case–control studies Target group: children aged 4–17 years | Pesticides were included in the group of organic contaminants (OCs). Practically no effect for OCs on ADHD outcome was ascertained (OR 0.99, 90% CI 0.96–1.02). The certainty of the evidence was considered ‘very low’ by GRADE standards. |
Pesticides | Roberts, J.R. et al. (2019). Children’s low-level pesticide exposure and associations with autism and ADHD: A review. Pediatric Research, 85(2), 234–241 [36]. | USA Costa Rica Taiwan Spain Belgium | n of studies: 12 n of participants: 13,007 (range 140–5193) Setting: cross-sectional, case–control and cohort studies Target group: children and mother–child pairs | In most of the included studies the outcome was ADHD, but also hand tremor, as an example, was used as a sign of ADHD. The level of pesticide exposure in the studies was generally low. Some kind of association between pesticides and ADHD or measures of attention was found in the majority of studies. However, the evidence could not be considered conclusive. |
Pesticides | Tessari et al. Association Between Exposure to Pesticides and ADHD or Autism Spectrum Disorder: A Systematic Review of the Literature. J Atten Disord. 2022 [37]. | Taiwan USA Canada Costa Rica Mexico Belgium Greenland Poland Ukraine France Slovakia Spain Norway Germany | n of studies: 15 n of participants: 15,132 (range 117–4437) Setting: cross-sectional, case–control and cohort studies Target group: children and mother–child pairs | Ten out of 15 studies reported a significant association between exposure to pesticides and ADHD/ADHD symptoms. The strengths of the association and the possible confounders controlled for varied substantially across studies. The evidence suggested a possible link between pesticides and ADHD, but heterogeneity across studies prevented firm conclusions. |
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Moore, S.; Paalanen, L.; Melymuk, L.; Katsonouri, A.; Kolossa-Gehring, M.; Tolonen, H. The Association between ADHD and Environmental Chemicals—A Scoping Review. Int. J. Environ. Res. Public Health 2022, 19, 2849. https://doi.org/10.3390/ijerph19052849
Moore S, Paalanen L, Melymuk L, Katsonouri A, Kolossa-Gehring M, Tolonen H. The Association between ADHD and Environmental Chemicals—A Scoping Review. International Journal of Environmental Research and Public Health. 2022; 19(5):2849. https://doi.org/10.3390/ijerph19052849
Chicago/Turabian StyleMoore, Sonja, Laura Paalanen, Lisa Melymuk, Andromachi Katsonouri, Marike Kolossa-Gehring, and Hanna Tolonen. 2022. "The Association between ADHD and Environmental Chemicals—A Scoping Review" International Journal of Environmental Research and Public Health 19, no. 5: 2849. https://doi.org/10.3390/ijerph19052849