Question

What are the main limitations of environmental epidemiology studies

Answer 1

Environmental epidemiology focuses on the health effects of environmental factors that are outside the immediate control of the individual. In industrialized countries, environmental epidemiologists often must assess a large number of low-level intercorrelated exposures, which often occur in complex mixtures. In that respect, environmental epidemiology is similar to nutritional epidemiology, except that environmental exposures usually are involuntary and do not differ significantly among individuals within one area. A typical example is contamination of community drinking water supplies, which affects all residents more or less equally. The relative increases in disease risks due to environmental exposures usually are very low, typically below 1.5. In addition, most chronic diseases of interest in environmental epidemiology, have other, much stronger determinants than environmental exposure. This leads to problems with controlling for confounding. Therefore, research findings often have been inconclusive. This is especially true for several new areas of research, such as electromagnetic fields and cancer, but is true even for several classical environmental health problems, such as passive smoking and radon. Thus, the future of environmental epidemiology often is seen as primarily involving even more research on these same exposures, using more powerful research methods. Many of the problems of environmental epidemiology become especially severe during local field investigations in response to acute public health problems, such as a cluster of cancer in a neighborhood or around a point source. In this situation, the level of exposure is often low and may have happened in the distant past. Often there is no clear hypothesis, the small number of residents gives sufficient power to detect only relative risks that are unrealistically high in the environmental setting, or the latency period may be insufficient. Case-control studies done in this situation, where the outcome is a chronic disease such as cancer, usually have been disappointing because it is rarely possible to reconstruct personal exposures accurately. Furthermore, environmental epidemiologists may be unprepared to address other health outcomes and issues of public concern, such as psychological effects, aesthetic values, social disruption, or effects on property values which may be the main concern of the public. A large number of environmental exposures means that environmental epidemiology, more than many other fields of epidemiology, needs to prioritize the issues to be studied. The current emphasis on molecular epidemiology means that a hypothesis may be chosen for study simply because a new methodology has become available, rather than because the hypothesis is important for science or public health. Such an approach can lead to the neglect of other, potentially much greater public health problems, such as the long-term effects of environmental decisions on local and global ecosystems. Ultimately, the survival of the human race depends on the survival of the global ecosystem, the atmosphere, arable land, ocean fisheries, freshwater supplies, and biodiversity. These systems are increasingly taxed by overconsumption, overpopulation, and wasteful technologies. The best-known examples are the depletion of ozone in the upper atmosphere and climatic warming. Ozone protects the earth from excessive ultraviolet (UV) radiation, which increases the risk of skin cancer and cataracts. Climatic warming may be associated with a large variety of effects, such as an increased number of deaths from heat waves and other weather extremes, the spread of infectious diseases, declining crops, and major societal disruption from loss of habitable land through flooding. To increase understanding of the potential health consequences of these changes, environmental epidemiologists must develop new methods of study and new interdisciplinary collaborations.