2.1. Study participants

The Health Effects of Arsenic Longitudinal Study (HEALS) in Araihazar, Bangladesh is a prospective cohort study designed to assess the effects of exposure to arsenic through drinking water on health. Details of the participant selection, study design, and study methods have been described previously (Ahsan et al., 2005). In brief, 11,746 male and female participants were recruited between 2000 and 2002 in Araihazar, Bangladesh. The study location is in a rural area with relatively homogeneous sociocultural characteristics. The cohort has been expanded in subsequent years but the current study is conducted among this original cohort. Demographic and lifestyle data as well as blood (from which TL is measured) and urine samples were collected at baseline. In-person visits were conducted every two years following the baseline visit and each visit included a physical examination and collection of urine. All subjects in the study received basic medical care through the study clinic. Informed consent was obtained from all study participants, and the study protocol was approved by the Institutional Review Boards of the University of Chicago, Columbia University, and the ethical committee of the Bangladesh Medical Research Council.