This seminal article, “An Evidence-Based Medicine Methodology To Bridge The Gap Between Clinical And Environmental Health Sciences,” addresses a critical void in public health and clinical practice: the lack of systematic, evidence-based guidance on the health impacts of environmental chemical exposures. Authored by Tracey J. Woodruff, Patrice Sutton, and The Navigation Guide Work Group, the paper highlights how widespread exposure to environmental chemicals in daily life—such as polybrominated diphenyl ethers (PBDEs) from flame retardants, phthalates in plastics, and persistent organochlorine pesticides like DDT—can profoundly and adversely affect reproductive and developmental health.
The urgency of this issue is underscored by the fact that virtually all pregnant women in the United States have detectable levels of various environmental chemicals in their bodies, including lead, mercury, bisphenol A (BPA), and several phthalates, pesticides, perfluorochemicals (PFCs), polychlorinated biphenyls (PCBs), and PBDEs. Alarmingly, many of these detected levels are already associated with adverse health outcomes in human studies. Exposures during critical periods of growth and development, particularly in utero and during infancy, childhood, and adolescence, are of particular concern due to their potential for profound and lasting health effects.
Despite the voluminous and growing body of scientific evidence on environmental chemicals and their health effects, this information remains largely unfamiliar and inaccessible to health professionals, especially those caring for individuals of childbearing age. This creates a significant “gap” between environmental health science and clinical practice, making it challenging for clinicians, patients, and policymakers to leverage this knowledge effectively. There is currently no trusted, readily available reference that provides timely, evidence-based advice on environmental contaminants.
To bridge this crucial divide, the authors embarked on an interdisciplinary collaboration to create The Navigation Guide. This innovative methodology is designed to:
- Systematically evaluate the quality of scientific evidence linking environmental exposures to reproductive and developmental health outcomes.
- Support evidence-based decision-making by clinicians, enabling them to counsel patients about hazardous exposures and preventative measures.
- Facilitate the development of prevention-oriented guidelines by professional societies, healthcare organizations, and government agencies for use in both clinical and policy settings.
The impetus for this clinical intervention stems from the recognition that while regulatory improvements for chemicals are fundamental, clinical practice offers a complementary and immediate point of intervention. Pediatricians have historically embraced this role, with the American Academy of Pediatrics having an environmental health committee for over fifty years and publishing a clinician handbook on preventing childhood diseases linked to environmental exposures. The authors contend that similar proactive approaches are equally relevant to reproductive health, given the importance of preconception and prenatal environmental exposures. Many prospective parents are intensely interested in environmental impacts, while many others are unaware that their home, workplace, and community environments could influence fertility and their future children’s health.
The Navigation Guide builds upon the well-established GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) system, which systematically rates evidence quality and grades the strength of recommendations. However, the authors emphasize that GRADE and other traditional evidence-based medicine methodologies have significant limitations in their direct applicability to environmental health science. These limitations stem from two key differences:
- Evidence-Stream Differences:
- GRADE primarily considers human experimental and observational evidence, assuming that in vitro and in vivo toxicity data have been adequately addressed by regulatory processes before pharmaceuticals enter the market.
- In stark contrast, the vast majority of environmental chemicals enter the marketplace without comprehensive and standardized information on their reproductive or other chronic toxicities. Therefore, The Navigation Guide explicitly incorporates studies from humans, laboratory animals, and other nonhuman streams of evidence when rating quality, recognizing that randomized controlled trials on environmental contaminants are often ethically impossible.
- Decision-Context Differences:
- Clinical decisions for medical interventions (like pharmaceuticals) typically involve a risk-benefit analysis, where exposure is justified by a potential health benefit greater than known risks. The “gold standard” for this is a randomized controlled trial.
- For environmental chemicals, however, the “benefits” are usually not health-directed, and exposures are often involuntary and widespread. There is no comparable comprehensive weighing of health benefits and risks in the environmental arena.
The Methodology of The Navigation Guide involves four systematic steps:
- Specify The Study Question: This initial step involves framing a specific, health-care relevant question about whether human exposure to a particular chemical or class of chemicals poses a reproductive health risk (e.g., “Does maternal exposure to perfluorooctane sulfonate affect fetal growth?”).
- Select The Evidence: This involves a systematic and documented search for both published and unpublished evidence. Importantly, The Navigation Guide does not incorporate most existing lists of reproductive or developmental toxicants because their compilation methods are often varied, unsystematic, or non-transparent.
- Rate The Evidence: Consistent with GRADE, individual studies and the overall body of evidence are systematically rated based on explicit criteria. Given the nature of environmental health evidence, this process is conducted for studies of humans, laboratory animals, and other nonhuman evidence streams. An additional step integrates these quality ratings to result in one of five possible statements about the overall strength of evidence for a particular environmental exposure: “known to be toxic,” “probably toxic,” “possibly toxic,” “not classifiable,” or “probably not toxic” to reproductive or developmental health.
- Grade The Strength Of The Recommendations: In the final step, the determined strength of evidence on toxicity is integrated with information about exposure levels, the availability of less toxic alternatives, and patients’ values and preferences. The outcome is a concise, evidence-based recommendation for prevention, offering guidance such as, “Chemical X is known to be toxic to reproductive health. Doing x, y, or z to prevent exposure is strongly recommended. Doing a, b, or c is discretionary”.
Future Directions and Broader Implications:
The authors emphasize the “enormous potential to reduce harm and associated health costs” by bridging the gap between clinical and environmental health sciences through the Navigation Guide. They envision professional societies, healthcare organizations, and government agencies utilizing this transparent and systematic framework to craft consistent and timely recommendations for improving patient and population health. The article also acknowledges that evidence streams are rapidly evolving in both clinical and environmental health sciences, necessitating constant review and incorporation of the most current approaches. The future role of electronic health records is highlighted as a potential “revolution” in medical research, accelerating knowledge creation about the environment’s impact on human health by facilitating the compilation of instant and longitudinal data.
Ultimately, the article connects this initiative to historical public health advancements, noting that just as the thalidomide tragedy of the 1950s and 1960s led to strengthened drug safety regulations, recent advancements in toxicity testing and understanding environmental health risks will likely result in significant changes in chemical toxicity data. The Navigation Guide provides a crucial framework to translate these complex data into timely, prevention-oriented guidelines for clinicians and patients, with the overarching goal of improving patient and population health.
Tracey J. Woodruff, the lead author, is the director of the Program on Reproductive Health and the Environment at the University of California, San Francisco, and an associate professor in the Department of Obstetrics, Gynecology, and Reproductive Sciences, with extensive research and policy development experience in environmental health, particularly concerning early-life development.
Reference: Woodruff, T. J., Sutton, P., & The Navigation Guide Work Group. (2011). An Evidence-Based Medicine Methodology To Bridge The Gap Between Clinical And Environmental Health Sciences. Health Affairs, 30(5), 931–937. https://doi.org/10.1377/hlthaff.2010.1219