Table 1.
Summary of studies providing moderate to high evidence of the association between ADHD and each of lead (Pb), phthalates (PhPl) and bisphenol A (BPA).
| 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. |
1 DSM ADHD (total), hyperactivity, impulsiveness and inattention diagnoses (DSM-IV or comparable system used). 2 DSM ADHD (total) diagnoses (DSM-IV or comparable system used). 3 This study analyzed studies on phthalates and bisphenol A in a combined “phthalates/plasticizers” category; odds ratio, OR; confidence interval, CI; DSM, Diagnostic and Statistical Manual of Mental Disorders.