Persistent organic pollutants (POPs) include hundreds of different chemical compounds with common properties, such as long-term persistence, widespread diffusion in the environment and bioaccumulation through the food chain.^1–3 In various species, POPs are linked to cancer, neurobehavioural disorders, impaired immunity, endocrine problems and reproductive disorders. Most epidemiological findings to date have focused on people with high exposure to POPs in occupational or accidental settings, whereas people without such high exposure have been much less studied; with few exceptions, this approach has uncovered only modest associations with various health outcomes.^2,4

POPs are detectable in virtually all of the general population, most of whom experience only background exposure through food consumption^1–3; a substantial body of biological, clinical and epidemiological knowledge suggests that such chronic low-level exposure is unlikely to be risk-free. An example useful for the discussion on this issue is provided by a recent study conducted by our research groups in Korea and Minnesota, based on a random sample of the US general population—that is, a sample with only background exposure to POPs.⁵ The study found a rather striking positive dose–response relationship between prevalence of type 2 diabetes and serum concentrations of several individual POPs, as well as with a summary or composite of the serum concentrations of six of the POPs with highest concentrations. After adjusting for known risk factors for diabetes, and compared with people with non-detectable POPs, the prevalence of type 2 diabetes increased by 15–40-fold among those with detectable concentrations of POPs.⁵ Undoubtedly, we should be cautious about this finding: it is cross-sectional and has not been replicated, although it is in line with several previous findings.

Remarkably, no prospective study on the potential relationship between body burden of POPs …