Kathleen L. Caldwell

Trends in Blood Lead Levels and Blood Lead Testing Among US Children Aged 1 to 5 Years, 1988–2004

OBJECTIVES. To evaluate trends in childrens blood lead levels and the extent of blood lead testing of children at risk for lead poisoning from national surveys conducted during a 16-year period in the United States. METHODS. Data for children aged 1 to 5 years from the National Health and Nutrition Examination Survey III Phase I, 1988–1991, and Phase II, 1991–1994 were compared to data from the survey period 1999–2004. RESULTS. The prevalence of elevated blood lead levels, ≥10 μg/dL, among children decreased from 8.6% in 1988–1991 to 1.4% in 1999–2004, which is an 84% decline. From 1988–1991 and 1999–2004, childrens geometric mean blood lead levels declined in non-Hispanic black (5.2–2.8 μg/dL), Mexican American (3.9–1.9 μg/dL), and non-Hispanic white children (3.1 μg/dL to 1.7 μg/dL). However, levels continue to be highest among non-Hispanic black children relative to Mexican American and non-Hispanic white children. Blood lead levels were distributed as follows: 14.0% were <1.0 μg/dL, 55.0% were 1.0 to <2.5 μg/dL, 23.6% were 2.5 to <5 μg/dL, 4.5% were 5 to <7.5 μg/dL, 1.5% were 7.5 to <10 μg/dL, and 1.4% were ≥10 μg/dL. Multivariable analysis indicated that residence in older housing, poverty, age, and being non-Hispanic black are still major risk factors for higher lead levels. Blood lead testing of Medicaid-enrolled children increased to 41.9% from 19.2% in 1988–1991. Only 43.0% of children with elevated blood lead levels had previously been tested. CONCLUSIONS. Childrens blood lead levels continue to decline in the United States, even in historically high-risk groups for lead poisoning. To maintain progress made and eliminate remaining disparities, efforts must continue to test children at high risk for lead poisoning, and identify and control sources of lead. Coordinated prevention strategies at national, state, and local levels will help achieve the goal of elimination of elevated blood lead levels.

Urinary perchlorate and thyroid hormone levels in adolescent and adult men and women living in the United States.

Background Perchlorate is commonly found in the environment and known to inhibit thyroid function at high doses. Assessing the potential effect of low-level exposure to perchlorate on thyroid function is an area of ongoing research. Objectives We evaluated the potential relationship between urinary levels of perchlorate and serum levels of thyroid stimulating hormone (TSH) and total thyroxine (T4) in 2,299 men and women, ≥ 12 years of age, participating in the National Health and Nutrition Examination Survey (NHANES) during 2001–2002. Methods We used multiple regression models of T4 and TSH that included perchlorate and covariates known to be or likely to be associated with T4 or TSH levels: age, race/ethnicity, body mass index, estrogen use, menopausal status, pregnancy status, premenarche status, serum C-reactive protein, serum albumin, serum cotinine, hours of fasting, urinary thiocyanate, urinary nitrate, and selected medication groups. Results Perchlorate was not a significant predictor of T4 or TSH levels in men. For women overall, perchlorate was a significant predictor of both T4 and TSH. For women with urinary iodine < 100 μg/L, perchlorate was a significant negative predictor of T4 (p < 0.0001) and a positive predictor of TSH (p = 0.001). For women with urinary iodine ≥ 100 μg/L, perchlorate was a significant positive predictor of TSH (p = 0.025) but not T4 (p = 0.550). Conclusions These associations of perchlorate with T4 and TSH are coherent in direction and independent of other variables known to affect thyroid function, but are present at perchlorate exposure levels that were unanticipated based on previous studies.

Relation between Cord Blood Mercury Levels and Early Child Development in a World Trade Center Cohort

Objective This study was designed to determine whether prenatal mercury exposure, including potential releases from the World Trade Center (WTC) disaster, adversely affects fetal growth and child development. Methods We determined maternal and umbilical cord blood total mercury of nonsmoking women who delivered at term in lower Manhattan after 11 September 2001, and measured birth outcomes and child development. Results Levels of total mercury in cord and maternal blood were not significantly higher for women who resided or worked within 1 or 2 miles of the WTC in the month after 11 September, compared with women who lived and worked farther away. Average cord mercury levels were more than twice maternal levels, and both were elevated in women who reported eating fish/seafood during pregnancy. Regression analyses showed no significant association between (ln) cord or maternal blood total mercury and birth outcomes. Log cord mercury was inversely associated with the Bayley Scales of Infant Development psychomotor score [Psychomotor Development Index (PDI)] at 36 months (b = –4.2, p = 0.007) and with Performance (b = –3.4, p = 0.023), Verbal (b = –2.9, p = 0.023), and Full IQ scores (b = –3.8, p = 0.002) on the Wechsler Preschool and Primary Scale of Intelligence, Revised (WPPSI-R), at 48 months, after controlling for fish/seafood consumption and other confounders. Fish/seafood consumption during pregnancy was significantly associated with a 5.6- to 9.9-point increase in 36-month PDI, and 48-month Verbal and Full IQ scores. Conclusions Blood mercury was not significantly raised in women living or working close to the WTC site in the weeks after 11 September 2001. Higher cord blood mercury was associated with reductions in developmental scores at 36 and 48 months, after adjusting for the positive effects of fish/seafood consumption during pregnancy.

Iodine Status of the U.S. Population, National Health and Nutrition Examination Survey, 2005–2006 and 2007–2008

BACKGROUND This report presents urinary iodine (UI) concentrations for the general U.S. population during 2005-2006 and 2007-2008. These findings are the fourth and fifth assessments of the population since National Health and Nutrition Examination Survey (NHANES) III (1988-1994), when the median UI concentration for the population decreased from NHANES I (1971-1974). METHODS During 2005-2006 and 2007-2008, ~ 5000 participants per year were selected to participate in NHANES. The participants were interviewed and examined. UI concentration was measured on a random one third subsample of 2649 participants, aged 6 years and older in 2005-2006, and in all participants in 2007-2008. These urine iodine concentrations are representative of the general U.S. population by age, sex, and race/ethnicity. RESULTS (i) The median UI concentrations for the general U.S. population in 2005-2006 and 2007-2008 were 164 mg/L (95% confidence interval [CI] 154-174) and 164 mg/L (95% CI 154-173), respectively. Also, the proportions of the population with a UI concentration of < 50 mg/L during these survey periods were 9.8% ± 1.3% and 8.8% ± 0.4%, respectively. The median UI concentration and prevalence of ≥ 200 mg/L appeared to be higher in children and persons ≥ 70 years than in other age groups. (ii) In both surveys, children aged 6-11 years had median UI concentrations of ≥ 200 mg/L, and about 5% of them had a UI concentration of < 50 mg/L. (iii) All pregnant women (sample size 184) surveyed during 2005-2008 had a median UI concentration of 125 mg/L (95% CI 86-198), and 56.9% ± 7.9% of this group had a UI concentration of < 150 mg/L. UI concentrations were lower among non-Hispanic black survey participants than non-Hispanic white and Mexican-American participants. CONCLUSIONS These findings affirm the stabilization of UI concentration and adequate iodine nutrition in the general U.S. population since 2000. However, certain groups likely do not achieve a sufficient dietary iodine intake according to the World Health Organization. The needs of these vulnerable groups and the inadequacy of their dietary iodine intake should be addressed in future efforts.

Iodine Status of the U.S. Population, National Health and Nutrition Examination Survey 2003–2004

BACKGROUND Since 1971, the general U.S. population has been monitored for dietary iodine sufficiency by urinary iodine (UI) measurements through the National Health and Nutrition Examination Survey (NHANES). This report presents the UI levels for the population participating in NHANES 2003-2004. It is the third assessment of the U.S. population since NHANES III (1988-1994), when the median UI level was observed to decrease from NHANES I (1971-1974). METHODS In 2003-2004, a stratified, multistage, probability sample of approximately 5000 participants per year were selected to participate in NHANES Household interviews, and specimen collection were performed. UI level was measured by inductively coupled plasma mass spectrometry on a random subsample of 2526 participants aged 6 years and older. RESULTS The median UI level for the general U.S. population in 2003-2004 was 160 microg/L (95% confidence interval [CI] 146-172), and 11.3 +/- 1.8% of the population had a UI level below 50 microg/L. Children had a higher UI level than adolescents and adults. Among all (pregnant and nonpregnant) women of reproductive age, the median UI level was 139 microg/L (95% CI 117-156), 15.1 +/- 3.2% women had a UI level <50 microg/L, and Non-Hispanic blacks in this group had a lower UI level than other racial/ethnic groups. CONCLUSIONS These findings affirm the stabilization of the UI level and the adequate iodine nutrition in the general U.S. population since 2000. Future surveys designed to achieve UI levels representative of pregnant women can improve the estimate of iodine sufficiency in this population subgroup. Continued monitoring of the population for iodine sufficiency is warranted because of groups at risk for iodine deficiency disorders.

Iodine Status in Pregnant Women in the National Children's Study and in U.S. Women (15–44 Years), National Health and Nutrition Examination Survey 2005–2010

BACKGROUND This report presents iodine data from National Health and Nutrition Examination Survey (NHANES) and from a sample of pregnant women in the National Childrens Study (NCS) Vanguard Study. METHODS Urinary iodine (UI) was measured in a one third subsample of NHANES 2005-2006 and 2009-2010 participants and in all 2007-2008 participants age 6 years and older. These measurements are representative of the general U.S. population. UI was also measured in a convenience sample of 501 pregnant women enrolled in the NCS initial Vanguard Study from seven study sites across the United States. RESULTS NHANES median UI concentration in 2009-2010 (144 μg/L) was significantly lower than in 2007-2008 (164 μg/L). Non-Hispanic blacks had the lowest UI concentrations (131 μg/L) compared with non-Hispanic whites or Hispanics (147 and 148 μg/L, respectively). The median for all pregnant women in NHANES 2005-2010 was less than adequate (129 μg/L), while third trimester women had UI concentrations that were adequate (median UI 172 μg/L). Third trimester women participating in the NCS similarly had an adequate level of iodine intake, with a median UI concentration of 167 μg/L. Furthermore, NCS median UI concentrations varied by geographic location. CONCLUSIONS Dairy, but not salt, seafood, or grain consumption, was significantly positively associated with median UI concentration in women of childbearing age. Pregnant women in their third trimester in the NHANES 2005-2010 had adequate median UI concentrations, but pregnant women in NHANES who were in their first or second trimesters had median UI concentrations that were less than adequate. Non-Hispanic black pregnant women from both the NHANES 2005-20010 and the NCS consistently had lower UI median concentrations than non-Hispanic whites or Hispanics.

Total blood mercury concentrations in the U.S. population: 1999-2006

We describe the distribution and demographic characteristics of total blood Hg levels in the U.S. general population among persons ages 1 year and older who participated in the 2003-2006 National Health and Nutrition Examination Survey (NHANES). We also describe trends in the total blood Hg of children ages 1-5 (n=3456) and females ages 16-49 during 1999-2006 (n=7245). In the combined 2003-2006 survey periods, the geometric means for non-Hispanic blacks, 0.853microg/L (95% confidence interval [CI], 0.766-0.950microg/L), and non-Hispanic whites, 0.833microg/L (95% CI, 0.752-0.922microg/L), were higher than the geometric mean for Mexican Americans, 0.580microg/L (95% CI, 0.522-0.645microg/L). Also in 2003-2006, regression analysis of log total blood Hg with age, race/ethnicity and gender showed that total blood Hg levels in the population exhibited a quadratic increase with age (p<0.0001), peaking at ages 50-59 in non-Hispanic blacks and whites, at ages 40-49 in Mexican Americans, and then declining at older ages. Over the four survey periods (1999-2006), regression analysis showed that total blood Hg levels increased slightly for non-Hispanic white children and decreased slightly for non-Hispanic black and Mexican American children. Over the same four survey periods, female children had slightly higher total blood Hg levels than males (0.356 vs. 0.313microg/L, p=0.0050) and total blood Hg levels in non-Hispanic black women aged 16-49 years were significantly higher than in non-Hispanic white women (1.081 vs. 0.850microg/L, p<0.0001) and in Mexican American women (1.081 vs. 0.70microg/L, p<0.0001).

Reduction in cadmium exposure in the United States population, 1988-2008: the contribution of declining smoking rates.

Background: Public health policies such as tobacco control, air pollution reduction, and hazardous waste remediation may have reduced cadmium exposure among U.S. adults. However, trends in urine cadmium, a marker of cumulative cadmium exposure, have not been evaluated. Objectives: We estimated the trends in urine cadmium concentrations in U.S. adults using data from the National Health and Nutrition Examination Surveys (NHANES) from 1988 to 2008. We also evaluated the impact of changes in the distribution of available cadmium determinants (age, sex, race, education, body mass index, smoking, and occupation) at the population level to explain cadmium trends. Methods: The study population included 19,759 adults ≥ 20 years of age with measures of urine cadmium and cadmium determinants. Results: Age-adjusted geometric means of urine cadmium concentrations were 0.36, 0.35, 0.27, 0.27, 0.28, 0.25, and 0.26 µg/g creatinine in 1988–1991, 1991–1994, 1999–2000, 2001–2002, 2003–2004, 2005–2006, and 2007–2008, respectively. The age, sex, and race/ethnicity-adjusted percent reduction in urine cadmium geometric means comparing 1999–2002 and 2003–2008 with 1988–1994 were 27.8% (95% confidence interval: 22.3%, 32.9%) and 34.3% (29.9%, 38.4%), respectively (p-trend < 0.001), with reductions in all participant subgroups investigated. In never smokers, reductions in serum cotinine accounted for 15.6% of the observed reduction. In ever smokers, changes in smoking cessation, and cumulative and recent dose accounted for 17.1% of the observed reduction. Conclusions: Urine cadmium concentrations decreased markedly between 1988 and 2008. Declining smoking rates and changes in exposure to tobacco smoke may have played an important role in the decline of urine cadmium concentrations, benefiting both smokers and nonsmokers. Cadmium has been associated to several health outcomes in NHANES 1999–2008. Consequently, despite the observed decline, further reduction in cadmium exposure is needed.

Validity of predictive equations for 24-h urinary sodium excretion in adults aged 18–39 y

BACKGROUND Collecting a 24-h urine sample is recommended for monitoring the mean population sodium intake, but implementation can be difficult. OBJECTIVE The objective was to assess the validity of published equations by using spot urinary sodium concentrations to predict 24-h sodium excretion. DESIGN This was a cross-sectional study, conducted from June to August 2011 in metropolitan Washington, DC, of 407 adults aged 18-39 y, 48% black, who collected each urine void in a separate container for 24 h. Four timed voids (morning, afternoon, evening, and overnight) were selected from each 24-h collection. Published equations were used to predict 24-h sodium excretion with spot urine by specimen timing and race-sex subgroups. We examined mean differences with measured 24-h sodium excretion (bias) and individual differences with the use of Bland-Altman plots. RESULTS Across equations and specimens, mean bias in predicting 24-h sodium excretion for all participants ranged from -267 to 1300 mg (Kawasaki equation). Bias was least with International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT) equations with morning (-165 mg; 95% CI: -295, 36 mg), afternoon (-90 mg; -208, 28 mg), and evening (-120 mg; -230, -11 mg) specimens. With overnight specimens, mean bias was least when the Tanaka (-23 mg; 95% CI: -141, 95 mg) or Mage (-145 mg; -314, 25 mg) equations were used but was statistically significant when using the Tanaka equations among females (216 to 243 mg) and the Mage equations among races other than black (-554 to -372 mg). Significant over- and underprediction occurred across individual sodium excretion concentrations. CONCLUSIONS Using a single spot urine, INTERSALT equations may provide the least biased information about population mean sodium intakes among young US adults. None of the equations evaluated provided unbiased estimates of individual 24-h sodium excretion.

Use of Inductively Coupled Plasma Mass Spectrometry to Measure Urinary Iodine in NHANES 2000: Comparison with Previous Method

Urinary iodine (UI) concentrations directly reflect dietary iodine intake and consequently test biochemical assessment of the iodine status worldwide (1). The Iodine Laboratory of the Division of Laboratory Sciences at the National Center for Environmental Health, CDC, measured the UI content of specimens as part of the National Health and Nutrition Examination Survey (NHANES) 2000 and will measure UI in the US population through future NHANES analyses, using inductively coupled plasma mass spectrometry (ICP-MS). In this report, we describe the ICP-MS laboratory method and compare that method with the established Sandell–Kolthoff (S-K) spectrophotometric method used in NHANES III. The ICP-MS method described previously (2) was modified for use in NHANES 2000 by adding alkaline diluents and rinses to measure UI as follows: urine samples and the urine iodide calibrator solutions were prepared just before analysis by dilution (1:49; 50 μL of sample/calibrator plus 2450 μL of diluent) with an aqueous solution of 10 mL/L tetramethylammonium hydroxide containing 10 μg/L tellurium as an internal standard. A peristaltic pump introduced the diluted samples into the spray chamber with an argon stream. The I+ and Te+ ions were measured at m/z 127 and 130, respectively (3). The diluent used to make the intermediate working calibrators was 1.0 g of analytical-reagent-grade sodium thiosulfate (Na2S2O3) dissolved in 1000 mL of 18 MΩ · cm ultrapure water. (The water used for all dilutions and rinses in the ICP-MS method is ultrapure 18 MΩ · cm water; Millipore Corporation.) The wash solution was an aqueous solution of 1 mL/L Triton X-100 and 10 mL/L tetramethylammonium hydroxide. This solution was …