DDT and Obesity in Humans: Exploring the Evidence in a New Way

Although conventional wisdom holds that overeating and a sedentary lifestyle are the main causes of obesity, increasing evidence indicates that additional risk may be conferred by exposure to obesogens, environmental chemicals suspected of influencing the development and maintenance of adipose (fat) tissue.1234 The insecticide dichlorodiphenyltrichloroethane (DDT) and its breakdown products are among many such suspected obesogens. A systematic review and meta-analysis in Environmental Health Perspectives now concludes that the collective evidence supports the presumption that DDT is a human obesogen. The excess accumulation of body fat can cause adverse health effects including diabetes, cardiovascular disease, and cancer. Obesogens are thought to disrupt the molecular mechanisms controlling the development and maintenance of adipose tissue. This disruption has the potential to produce larger and more numerous fat cells, which could in turn lead to obesity and related complications. Obesogens can also alter programing of metabolic set points, appetite, and satiety. From the 1940s to the 1970s, DDT was used widely to control mosquitoes and the diseases they transmit.78 As a result of concerns about its adverse effects on wildlife and humans and its persistence in the environment, its use was largely banned, although it is still used in some countries to fight mosquito-borne diseases. Despite the relatively limited use today, DDT is highly persistent in the human body, and most people throughout the world carry at least traces of it and its metabolites in their bodies.58 The current review evaluated the body of research on DDT as an obesogen using what is known as the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. The authors applied this approach with guidance from two sources: the Handbook for Conducting a Literature-Based Health Assessment published by the National Toxicology Program Office of Health Assessment and Translation (OHAT), and the Navigation Guide developed by a work group of nearly two dozen environmental health experts. The GRADE approach originated as a means of methodically and rigorously assessing human studies in clinical medicine and public health. The OHAT Handbook and Navigation Guide adapt this approach to integrate lines of evidence from epidemiological, animal, and in vitro studies. Investigators can then systematically