The Association between obesity, central adiposity and endocrine disruptors

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DESCRIPTION (provided by applicant): The prevalence of obesity has increased several-fold over the last few decades in children, adolescents, and adults. Some evidence suggests that there has been a disproportionate increase in the level of central adiposity, which carries an even greater disease risk than peripheral fat. Changes in diet and exercise habits over the past few decades are undoubtedly linked to the current epidemic of overweight and obesity, and changes in the quality and composition of the diet may also play a role. Recently, interest has emerged in the possibility that environmental chemical contaminants may also contribute to the growing problem of obesity. Limited evidence from laboratory studies suggests that synthetic chemicals may affect obesity- related pathways by changing hormone levels or altering gene expression, but virtually no human studies have been conducted. In this proposed epidemiologic study, cross-sectional data on a sample of approximately 5000 participants, aged 6 years and older, from the 1999-2002 National Health and Nutrition Examination Survey (NHANES) will be analyzed to determine whether blood and urine levels of environmental contaminants are associated with level of body fat. The measures of body fat to be examined include body mass index, waist circumference, subscapular skin folds, and the amount and type of body fat, estimated using dual-energy x-ray absorptiometry (DXA). The study will examine the potential adverse effects of exposure to phthalates and heavy metals as well as the possible protective effects of phytoestrogens such as genestein on total body fat and the level of central adiposity. Potentially important interactions between these environmental exposures and age, gender, various dietary factors, activity levels will also be examined. Finally, the study includes a secondary analysis that takes advantage of the repeated NHANES surveys over four decades to answer the question of whether the level of central adiposity has increased over time in separate age, race, and gender subgroups, after adjusting for increases in BMI. This study is designed to use existing data to explore the novel hypothesis that environmental contaminants may, in part, be responsible for the increasing rates of total obesity and the increases in visceral fat deposition in children and adults. The strengths of the study include its large sample size, state-of-the-art measurements of environmental contaminants from blood and urine, precise measurements of BMI, DXA-derived measures of central adiposity, and extensive information on potential confounders and effect modifiers. The study is limited by its cross-sectional nature. Nevertheless, it may provide important clues for future, epidemiologic studies of the effect of these environmental contaminants on the risk of obesity.