Blood lead level association with lower body weight in NHANES 1999–2006
Introduction
In the last few decades, the prevalence of obesity in United States has increased in all age groups. In adults, the prevalence of obesity rose from 14.5% in NHANES I (1972–1974) to 35.1% in NHANES 2005–2006 (http://www.cdc.gov/nchs/data/hestat/overweight/overweight_adult.pdf). The prevalence of obesity in children and adolescents also increased, from 6.1% in 1972–1974 (NHANES I) to 18.1% in NHANES 2007–2008 (http://www.cdc.gov/nchs/data/hestat/obesity_child_07_08/obesity_child_07_08.pdf).
The rise in obesity coincides with increased exposure to environmental toxins — particularly those that have the characteristic of being hormone-mimetic such as estrogen mimics and endocrine disrupting chemicals (EDCs). Recently, Grun and Blumberg (2006) coined the term ‘obesogens’ to identify “chemicals that promote obesity either by increasing the number of fat cells or the storage of fat into existing fat cells”. Prenatal exposure to these obesogens may be an important risk factor for childhood and adult obesity (Janesick and Blumberg, 2011).
Exposure to lead (Pb) is hypothesized to influence growth during childhood. Prenatal exposure to lead is associated with low birth weight (Jelliffe-Pawlowski et al., 2006). During pregnancy, lead passes across the placenta from the mother's bloodstream to the fetal circulation (ATSDR, 2007). In the fetus, the lead competes with calcium for deposition in the fetal bone and may result in impaired growth (Zhu et al., 2010).
Epidemiological studies on the association of blood lead levels (BLL) with BMI or obesity are inconclusive. Kim et al. (1995) reported a weak but statistically significant positive association between childhood lead levels in teeth and BMI, whereas other studies did not or found an inverse association (Little et al., 2009). An inverse association between BMI and lead was also reported in adults (Padilla et al., 2010).
To investigate the correlation between BLL and weight outcomes, we analyzed data from NHANES 1999–2006 in children and adolescents (3–19 years old) and in adults (20 years and older). Body mass index was the measure of weight in the adult population (aged ≥ 20), and overweight and obese adults were defined based upon BMI measures of 25–29.9 and ≥ 30, respectively. We used age- and sex-standardized BMI Z-scores for children and adolescents as a measure of weight, and overweight and obese children were classified as having BMI Z-scores ≥ 85th and ≥ 95th percentiles, respectively.
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Study population
The NHANES studies from 1999 to 2006, conducted by the U.S. National Center for Health Statistics (NCHS; Centers for Disease Control and Prevention, CDC, Atlanta, GA) with biomonitoring data evaluated by the National Center for Environmental Health (NCEH), are cross-sectional, nationally representative surveys of the non-institutionalized civilian population of the United States (NCHS, 2008a). The grouping we used consisted of 4 cycles (1999–2000, 2001–2002, 2003–2004 and 2005–2006) that were
Children and adolescent (3–19 years old)
Table 1 illustrates the weighted characteristics of participants aged 3–19 years from NHANES 1999–2006 included in this study. The mean age of the participants was 11 years and approximately 51% were male. Non-Hispanic whites accounted for 60% of the total study group; 14.7% were non-Hispanic blacks, and 12.2% were Mexican-American. Approximately 23% of the participants were from families with income at the poverty level. The geometric mean (SE) BMI Z-score was 0.77 (0.01) and the geometric mean
Discussion
The results of this analyses support an inverse association of BLL and body weight outcomes in children and adolescents, and adults in the U.S. population. The inverse association is independent of confounding factors such as: age, gender, race/ethnicity, calorie intake, TV and video game use, poverty income rate, and serum cotinine in children and adolescents; and age, gender, race/ethnicity, education, alcohol consumption, cigarette smoking, environmental tobacco smoke exposure (through serum
Conclusion
We found that BLLs are associated with lower body mass index and obesity in children and adolescents, as well as in adults both when analyzing eight years of NHANES data combined (1999–2006) and when restricted to only four years at a time (1999–2002 and 2003–2006). Considering the similar finding for the Korean NHANES study, this association deserves additional study.
Conflict of interest
The authors declare that there are no conflicts of interest.
Acknowledgment
This research was supported in part by an appointment to the Research Participation Program at the Centers for Disease Control and Prevention administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and CDC (MCB).
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