Although we include many environmental pollutants that are widespread and available in NHANES, we were not able to account for all environmental pollutants as it is unrealistic, the data were not available and not all environmental pollutants have been identified as yet. Also, we limited our analysis to chemical environmental pollutants in constructing the ERS. Recently, a new concept of the exposome, that is, the totality of exposures over the course of a lifetime, has been proposed [60]–[65] and the need for more complete non-genetic exposure assessment in epidemiologic research has been emerging, as emphasized in the strategic themes defined by the National Institute of Environmental Health Sciences (NIEHS) (http://www.niehs.nih.gov/about/strategicplan/). Our proposed approach will be useful to identify important individual factors and to combine their risks, which eventually will advance our understanding of health responses to the complex nature of multi-pollutant exposures.
