Role of epidemiology in health risk assessment.

Human health risk assessment has been the object of systematic study in recent years, with formal models of risk assessment and risk management having been proposed by several national and international health agencies. The particular model developed by the Environmental Health Directorate of Health and Welfare Canada was examined in some detail and used to focus on the role of epidemiology in the overall process of risk assessment. In addition to providing information fundamental to the identification of environmental carcinogens and the estimation of carcinogenic risks, epidemiology may also play a role in shaping risk perception and in improving risk communication practices. Taken collectively, epidemiologic data on health risks provide a basis for improved disease surveillance and prioritization of public health concerns. Both descriptive and analytic epidemiologic protocols may be used to gather information on disease etiology. Because of the potential for bias and confounding in observational studies of human populations, epidemiological data should be subjected to careful evaluation in accordance with established criteria before a causal relationship between exposure and disease is inferred. Toxicological studies using nonhuman test systems may be used to avoid these problems, but at the expense of obtaining indirect information on human health risks. Nonetheless, toxicological data provide an important complement to epidemiological data, providing information on potential health risks in advance of human exposure and offering a means of indirectly assessing risks in situations where human studies fail to provide informative results. The complementary roles of epidemiology and toxicology in health risk assessment were examined using four case studies. While the epidemiological evidence linking tobacco consumption to lung cancer is now unequivocal, the corresponding data on involuntary smoking, although strongly suggestive of increasing the relative risk of lung cancer, requires further confirmation before providing the same degree of evidence as now exists for active smoking. At present, the best estimates suggest that overall mortality attributable to active smoking may exceed that due to passive smoking by roughly 100-fold. Despite this large difference in health impact, passive smoking continues to be the focus of much public concern, in part because of the involuntary nature of the risk involved. Because of the abundance of good epidemiological data on tobacco, toxicology has assumed a secondary role in defining the health risks associated with smoking. In contrast, while epidemiological studies with saccharin and formaldehyde have provided unequivocal evidence of carcinogenic effects in animals exposed to high doses, thereby raising concerns over potential human carcinogenicity.(ABSTRACT TRUNCATED AT 400 WORDS)