Association of blood trihalomethane concentrations with asthma in U.S. adolescents: nationally representative cross-sectional study.

BACKGROUND Population studies show that the use of swimming pools is associated with the risk of asthma and allergic diseases among children. OBJECTIVE To explore the associations between blood trihalomethane (THM) concentrations and asthma among U.S. adolescents and assess to what extent the association is modified by active tobacco smoke exposure. METHODS We included 2359 adolescents aged 12-19 years with measured blood concentrations of chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM) from the National Health and Nutrition Examination Surveys 2005-2012. Logistic regression models were fitted to assess the odds ratios (ORs) for the association of THM concentrations (three or four categories) with the risk of self-reported current and ever (lifetime) asthma. RESULTS Blood DBCM concentration was associated with a greater risk of ever asthma among all adolescents (OR=1.54; 95% confidence intervals: 1.07, 2.21, comparing the extreme exposure categories). The relation was stronger among adolescents exposed to tobacco smoke (OR=3.96; 1.89, 8.30, comparing the extreme exposure categories). We also found positive relationships between brominated THMs (sum of BDCM, DBCM, and TBM) and risk of ever asthma and between DBCM and brominated THMs and risk of current asthma among adolescents with tobacco smoke exposure. The relative excess risk of ever asthma due to the interaction between high blood DBCM and brominated THMs and tobacco smoke exposure was 1.87 (0.30, 3.43) and 0.78 (0.07, 1.49), respectively. CONCLUSIONS Exposure to THMs is associated with a greater risk of asthma in adolescents, particularly among those exposed to tobacco smoke.