Urine chemical content may be a false measure of environmental exposure.

Dr Trasande and his group in the article on phthalates conclude that urine phthalate concentrations (represented by urine di-2-ethylhexylphthalate [DEHP] concentrations) were associated with increased insulin resistance in this cross-sectional study of adolescents. Dr Trasande refers to this as an association and indicated that this study cannot rule out the possibility that insulin-resistant children ingest food with higher phthalate content or that insulin-resistant children excrete more DEHP. Without knowing the tissue or serum concentration of DEHP or referring to primate studies, the authors’ hypotheses are appropriate.