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Greater exposure to certain endocrine-disrupting chemicals (EDCs) was associated with higher risk of attention-deficit/hyperactivity disorder (ADHD) in teens, a new study found.

In an analysis of 205 adolescents and teens, every two-fold increase in antiandrogenic phthalate concentrations measured in urine samples came with 34% increased relative risk for ADHD (adjusted RR 1.34, 95% CI 1.00-1.79), reported Jessica Shoaff, PhD, of Brigham and Women's Hospital in Boston, and colleagues in

Higher exposure to antiandrogenic phthalates, measured by the sum of 11 individual phthalate chemicals, was specifically tied to an increase in hyperactivity problems for adolescents (aRR 1.40, 95% CI 1.07-1.84).

On the other hand, the team found, attention problems were not significantly associated with this type of EDC (aRR 1.26, 95% CI 0.87-1.83).

Although childhood exposure to antiandrogenic phthalates had the strongest link with ADHD symptoms, greater exposure to other EDCs also increased the risk for ADHD-related behavioral problems.

Specifically, every two-fold increase in urinary biomarker concentration of di(2-ethylhexyl) phthalate (DEHP) -- a type of phthalate chemical commonly used to make plastics more flexible -- was associated with a 29% increased risk for combined ADHD symptoms (aRR 1.29, 95% CI 1.07-1.55). DEHP exposure was tied to a 29% increased risk for attention problems and a 27% increased risk for hyperactivity problems.

Additionally, greater exposure to chemicals in personal care products -- measured in the analysis by the sum of mono-n-butyl phthalate, monohydroxybutyl phthalate, monoethyl phthalate, monoisobutyl phthalate, and monohydroxyisobutyl phthalate -- was linked to a 25% increased risk for hyperactivity problems in youth (aRR 1.25, 95% CI 1.07-1.47), but not attention issues.

Similarly, every two-fold increased concentration of dichlorophenols, measured by the sum of 2,4-dichlorophenol and 2,5-dichlorophenol, which are commonly found in pesticides, was linked to a 22% increased risk for hyperactivity in adolescents (aRR 1.22, 95% CI 1.04-1.42), but not to attention problems.

Only two types of EDCs showed no significant association with either attention or hyperactivity problems in youth: parabens, which are preservatives often used in cosmetics and personal care products; and bisphenols, which are commonly found in plastics.

"In a population with a high prevalence of ADHD-related behaviors, our findings support an association of adolescent exposure to EDCs, particularly select phthalates, with an increased risk of significant ADHD-related behavior problems at exposure biomarker concentrations typical of adolescents in the general U.S. population," Shoaff and co-authors wrote.

They said the findings were not particularly surprising, since by Shoaff and other members of the team had suggested a link between adolescent EDC exposure -- especially with antiandrogenic phthalates -- and a higher risk of externalizing behaviors in youth like hyperactivity, aggression, and conduct problems.

This may be the result of adolescence as a "critical period for brain development" as well as a time of "heightened vulnerability to EDC exposure," the researchers suggested.

For the cross-sectional analysis, they drew upon data from 205 participants in the New Bedford Cohort, an an ongoing prospective birth cohort. Adolescents underwent in-person neurodevelopmental testing around the age of 15, and spot urine samples were analyzed for 28 biomarkers of various phthalates, phenols, corresponding substitutes, and triclocarban.

Overall, adolescents tended to have greater exposure to phthalates, with median urine concentrations of 0.45 μmol/L of antiandrogenic phthalates and 0.49 μmol/L of personal care product phthalates, the researchers reported. Median concentrations were generally lower for all other types of EDCs: 0.13 μmol/L of DEHP metabolites, 0.35 μmol/L of parabens, 0.02 μmol/L of bisphenols, and 0.02 μmol/L of dichlorophenols.

The researchers called the identification of modifiable risk factors for ADHD "of great public health importance" and said the study findings "contribute new insights into the potential detrimental neurobehavioral outcomes of EDC exposure during adolescence."

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