Academic journal article Environmental Health Perspectives

The Epidemiology of Lead Toxicity in Adults: Measuring Dose and Consideration of Other Methodologic Issues

Academic journal article Environmental Health Perspectives

The Epidemiology of Lead Toxicity in Adults: Measuring Dose and Consideration of Other Methodologic Issues

Article excerpt

We review several issues of broad relevance to the interpretation of epidemiologic evidence concerning the toxicity of lead in adults, particularly regarding cognitive function and the cardiovascular system, which are the subjects of two systematic reviews that are also part of this mini-monograph. Chief among the recent developments in methodologic advances has been the refinement of concepts and methods for measuring individual lead dose in terms of appreciating distinctions between recent versus cumulative doses and the use of biological markers to measure these parameters in epidemiologic studies of chronic disease. Attention is focused particularly on bone lead levels measured by K-shell X-ray fluorescence as a relatively new biological marker of cumulative dose that has been used in many recent epidemiologic studies to generate insights into lead's impact on cognition and risk of hypertension, as well as the alternative method of estimating cumulative dose using available repeated measures of blood lead to calculate an individual's cumulative blood lead index. We review the relevance and interpretation of these lead biomarkers in the context of the toxicokinetics of lead. In addition, we also discuss methodologic challenges that arise in studies of occupationally and environmentally exposed subjects and those concerning race/ethnicity and socioeconomic status and other important covariates. Key words: adults, biomarkers, epidemiologic methods, epidemiology, lead, toxicity. Environ Health Perspect 115:455-462 (2007). doi:10.1289/ehp.9783 available via http://dx.doi.org/ [Online 22 December 2006]

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In the worlds of environmental health and environmental medicine, lead exposure remains one of the most important problems in terms of prevalence of exposure and public health impact. Despite decades of intensive research, lead toxicity also remains one of the most, if not the most, studied subjects of all within the fields of environmental health and environmental medicine. This reflects the large gaps that continue to exist in our understanding of the full implications of lead exposure on health: how lead exposure may impact on chronic diseases; what mechanisms dictate lead's health effects; how to predict, monitor, and manage lead toxicity; and what factors may modify lead's effects.

Epidemiologic studies form the body of research most relevant to anticipating human health effects and developing guidelines for preventing and managing human exposures. In recent years, we have seen great advances in their level of sophistication and design. Such advances allow greater inference in terms of issues critical to prevention and public health, such as potential causality, dose-response relationships, and susceptible subpopulations.

Two of the articles in this mini-monograph are reviews of the effects of lead on the cardiovascular system and upon cognitive function in adults (Navas-Acien et al. 2007; Shih et al. 2007). Issues of methodology determine the confidence to be placed on the validity of the evidence presented in such reviews and the strength of the appropriate inferences. In this present article we attempt to review and address the major methodologic issues common across studies. Chief among the recent developments in methodologic advances has been the refinement of concepts and methods for measuring individual lead dose. This includes appreciating distinctions between recent versus cumulative doses and acute versus chronic effects, as well as the use of biological markers in epidemiologic studies to measure these parameters. In this article, we review this topic in some depth.

We also address important issues related to epidemiologic design, such as cross-sectional versus longitudinal studies; community-based versus occupational studies; and the identification and control of bias and confounding. Our goal in this article is to provide the methodologic basis to interpret the major issues that are of relevance to the articles in the mini-monograph as well as future studies intending to investigate the effect of lead on health outcomes. …

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