Children with attention-deficit/hyperactivity disorder (ADHD) were found to have increased levels of monoethylhexyl phthalate (MEHP), mono-n-butyl phthalate (MnBP), and monobenzyl phthalate (MBzP) compared with children without ADHD, according to the results of a study published in European Child & Adolescent Psychiatry.

The case-control study sought to determine whether insulin-like growth factor-1 (IGF-1), IGF-binding protein-3 (IGFBP-3), thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free T4, phthalate, and bisphenol-A (BPA) levels were different in children with ADHD compared with those without ADHD.

Eligible study participants had a clinical diagnosis of ADHD according to the Diagnostic and Statistical Manual of Mental Disorders, were aged 6 to 12 years, were not taking any medications, and did not have a past or present comorbid neurodevelopmental or psychiatric disorder.

A total of 144 patients with ADHD (mean age, 8.9 years; 76.4% boys) and 70 control individuals without ADHD (mean age, 9.2 years; 65.7% boys) were included.

Children with ADHD had lower IGF-1 levels compared with the control group (141.5±69.5 ng/mL vs 182.7±100.8 ng/ mL, P =.003). The differences in IGF-1 levels between children with vs without ADHD remained significant (P =.003) after adjustment for age and sex. No significant differences in IGFBP3, T4, free T4, T3, or TSH levels were observed between the children with vs without ADHD.

In addition, children with ADHD had increased levels of MnBP (18.1±17.4 ng/mL vs 13.6±12.4 ng/mL, P =.033), MBzP (0.8±1.7 vs 0.5±0.6 ng/mL, P =.040), and MEHP (8.0±10.7 vs 5.7±5.5 ng/mL, P =.043) compared with children without ADHD.

Levels of MEHP (r = -0.309, P <.001) and BPA (r = -0.140, P =.041) were negatively correlated with IGF-1 levels. Also, IGF-1 levels were negatively correlated with clinical symptoms (r = -0.257, P <.01), Auditory Attention-Impulsivity score (r = -0.196, P <.01), and Visual Attention-Sluggish score (r = -0.137, P <.05).

The investigators noted that a causal inference of endocrine-disrupting chemical exposure, hormone secretion, and brain development cannot be determined. Furthermore, the sample size was relatively small, and the neurobiological mechanism underlying the observed correlations is undetermined as exposure could be influenced by diet, lifestyle, and/or socioeconomic status.

“These results demonstrate new insight that growth hormones and environmental chemicals’ exposure, particularly MEHP, may be involved in neurodevelopment maturation,” stated the researchers.

Reference

Wang L-J, Huang Y-H, Chou W-J, et al. Interrelationships among growth hormone, thyroid function, and endocrine‑disrupting chemicals on the susceptibility to attention‑deficit/hyperactivity disorder. Eur Child Adolesc Psychiatry. Published online February 4, 2022. doi:10.1007/s00787-021-01886-4