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Polyfluoroalkyl Chemicals in the U.S. Population: Data from the National Health and Nutrition Examination Survey (NHANES) 2003–2004 and Comparisons with NHANES 1999–2000 [1]

['Antonia M. Calafat', 'Lee-Yang Wong', 'Zsuzsanna Kuklenyik', 'John A. Reidy', 'Larry L. Needham']

Date: 2007-11-24

Abstract Background Polyfluoroalkyl chemicals (PFCs) have been used since the 1950s in numerous commercial applications. Exposure of the general U.S. population to PFCs is widespread. Since 2002, the manufacturing practices for PFCs in the United States have changed considerably. Objectives We aimed to assess exposure to perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and eight other PFCs in a representative 2003–2004 sample of the general U.S. population ≥ 12 years of age and to determine whether serum concentrations have changed since the 1999–2000 National Health and Nutrition Examination Survey (NHANES). Methods By using automated solid-phase extraction coupled to isotope dilution–high-performance liquid chromatography–tandem mass spectrometry, we analyzed 2,094 serum samples collected from NHANES 2003–2004 participants. Results We detected PFOS, PFOA, PFHxS, and PFNA in > 98% of the samples. Concentrations differed by race/ethnicity and sex. Geometric mean concentrations were significantly lower (approximately 32% for PFOS, 25% for PFOA, 10% for PFHxS) and higher (100%, PFNA) than the concentrations reported in NHANES 1999–2000 (p < 0.001). Conclusions In the general U.S. population in 2003–2004, PFOS, PFOA, PFHxS, and PFNA serum concentrations were measurable in each demographic population group studied. Geometric mean concentrations of PFOS, PFOA, and PFHxS in 2003–2004 were lower than in 1999–2000. The apparent reductions in concentrations of PFOS, PFOA, and PFHxS most likely are related to discontinuation in 2002 of industrial production by electrochemical fluorination of PFOS and related perfluorooctanesulfonyl fluoride compounds. Keywords: biomonitoring, C8, exposure, PFCs, PFOA, PFOS, prevalence, serum

Materials and Methods We obtained serum samples analyzed for PFCs from 2,094 participants ≥ 12 years of age from NHANES 2003–2004. The National Centers for Health Statistics Institutional Review Board reviewed and approved the study protocol. All participants provided informed written consent; parents or guardians provided consent for participants < 18 years of age (CDC 2006a). We measured perfluorooctane sulfonamide (PFOSA), 2-(N-ethyl-perfluorooctane sulfon-amido) acetic acid (Et-PFOSA-AcOH), 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (Me-PFOSA-AcOH), perfluorobutane sulfonic acid (PFBuS), perfluorohexane sulfonic acid (PFHxS), PFOS, PFOA, perfluoroheptanoic acid (PFHpA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDeA), perfluoroundecanoic acid (PFUA), and perfluorododecanoic acid (PFDoA) in 1 mL of serum, using a modification of the method of Kuklenyik et al. (2004), which involved automated solid-phase extraction coupled to reversed-phase high-performance liquid chromatography–tandem mass spectrometry. We used 18O 2 -PFOS (for all sulfonic acids and all amides) and 13C 2 -PFOA (for all carboxylic acids) for quantification. To compensate for the lack of isotope-labeled internal standards for the other analytes and to partially account for matrix effects, the calibration standards were spiked into calf serum. The limits of detection (LODs) ranged from 0.1 to 1.0 μg/L; the accuracy ranged from 84 to 135% at three concentrations (Kuklenyik et al. 2004); and the precision ranged from around 10 to 26% at two different levels ( ). Low-concentration (~ 3 μg/L to ~ 9 μg/L) and high-concentration (~ 10 μg/L to ~ 30 μg/L) quality-control (QC) materials, prepared from a base calf serum pool, were analyzed with reagent blank, serum blank, and NHANES samples (Kuklenyik et al. 2004). Standard, blank, QC, and NHANES samples were analyzed by the procedure described above. Table 1 Precisiona LOD (μg/L)b QCL QCH Analyte NHANES 2003–2004 NHANES 1999–2000 NHANES 2003–2004 NHANES 1999–2000 NHANES 2003–2004 NHANES 1999–2000 PFOSA 0.2 0.05 2.7 (14.9) 2.4 (14.1) 13.0 (16.3) 12.4 (12.5) Me-PFOSA-AcOH 0.6 0.2 3.4 (15.5) 3.1 (14.2) 9.1 (16.7) 9.0 (13.5) Et-PFOSA-AcOH 0.4 0.2 3.8 (17.2) 3.5 (14.3) 8.3 (19.2) 8.1 (15.6) PFBuS 0.4 ND 4.4 (18.2) ND 14.6 (15.1) ND PFHxS 0.3 0.1 2.5 (16.4) 2.1 (16.6) 11.9 (12.9) 11.2 (12.3) PFOS 0.4 0.2 8.9 (10.4) 8.8 (8.4) 31.4 (10.1) 31.6 (7.1) PFHpA 0.3 0.4 7.6 (17.0) 6.8 (13.5) 15.8 (14.3) 15.5 (12.0) PFOA 0.1 0.1 3.2 (10.0) 3.1 (8.5) 14.7 (10.9) 15.1 (7.3) PFNA 0.1 0.1 2.5 (15.0) 2.6 (15.4) 12.7 (13.2) 13.0 (10.9) PFDeA 0.3 0.2 2.4 (17.5) 2.2 (13.9) 8.5 (18.2) 8.4 (13.1) PFUA 0.3 0.2 1.9 (22.0) 2.0 (19.1) 9.9 (19.8) 10.6 (16.2) PFDoA 1.0 0.2 2.2 (25.6) 2.4 (22.4) 8.5 (25.7) 9.1 (19.3) Open in a separate window We analyzed the data using SAS (version 9.1.3; SAS Institute Inc., Cary, NC) and SUDAAN (version 9.0.1; Research Triangle Institute, Research Triangle Park, NC). SUDAAN calculates variance estimates after incorporating the sample population weights, designed for the one-third subset of the full survey, which account for unequal selection probabilities and planned oversampling of certain subgroups resulting from the complex multistage area probability design of NHANES. Race/ethnicity was defined on the basis of self-reported data as non-Hispanic black, non-Hispanic white, and Mexican American. Persons not defined by these groups were included only in the total population estimate. Age was reported in years at the most recent birthday. We estimated the weighted percentage of detection and calculated weighted geometric means and percentiles for the serum concentrations (in micrograms per liter) of the various PFCs. For concentrations below the LOD, as recommended for the analysis of NHANES data (CDC 2006b), we used a value equal to the LOD divided by the square root of 2 (Hornung and Reed 1990). Parametric statistics were computed only for analytes for which the frequency of detection was ≥ 60%. Because PFC concentrations were not normally distributed, we used the natural log transformation. Weighted Pearson correlation coefficients and related p-values were calculated in SAS. Statistical significance was set at p < 0.05. We used analysis of covariance to examine the influence of demographic and socioeconomic variables on the log-transformed serum concentrations of PFOS, PFOA, PFHxS, and PFNA. For multiple regression, we calculated the least square geometric means (LSGM) and compared them for each categorical variable. The variables included in the initial model were as follows: age as a continuous variable, sex, race/ethnicity, smoking status (yes/no), and education (less than high school, high school diploma, more than high school). Participants were categorized as smokers if their serum cotinine concentrations were > 10 μg/L. We chose to include education in the model without household income to minimize the possibility of collinearity because a) income and education are strongly associated (chi-square p = 0.001) and b) the final model yielded comparable results with either variable separately (except for PFOS, which included one additional significant term between income and smoking status). We assessed all possible two-way interaction terms in the model. To reach the final reduced model, we used backward elimination with a threshold of p < 0.05 for retaining the variable in the model, using Satterwaite adjusted F statistics. We evaluated for potential confounding by adding each of the excluded variables back into the final model one by one and examining changes in the β coefficients of the statistically significant main effect. If addition of one of these excluded variables caused a change in a β coefficient by ≥ 10%, the variable was re-added to the model.

Results The distribution of PFC serum concentrations is reported stratified by age, sex, and race/ethnicity ( – ). Four analytes were detected in > 98% of the samples (PFOS, 99.9%; PFOA, 99.7%; PFHxS, 98.3%; PFNA, 98.8%). Concentrations of these four PFCs ranged from < 0.4 μg/L to 435 μg/L (PFOS), < 0.1 μg/L to 77.2 μg/L (PFOA), < 0.3 μg/L to 82.0 μg/L (PFHxS), and < 0.1 μg/L to 11.5 μg/L (PFNA). Six other analytes were detected at lower frequencies: PFDeA (31.3%), Me-PFOSA-AcOH (27.5%), PFOSA (22.2%), PFUA (9.7%), PFHpA (6.2%), and Et-PFOSA-AcOH, (3.4%); their geometric mean and selected percentile concentrations are given as Supplemental Material in Tables S1–S6 (online at http://www.ehponline.org/docs/2007/10598/suppl.pdf). For the two analytes detected in < 1% of the samples (PFDoA, < 0.1%; PFBuS, 0.4%), we could not calculate the 95th percentile of concentrations. Table 2 Variable Geometric mean 10th percentile 25th percentile 50th percentile 75th percentile 90th percentile 95th percentile No. All 20.7 (19.2–22.3) 9.8 (9.0–10.8) 14.6 (13.8–15.2) 21.1 (19.8–22.4) 29.9 (27.5–32.8) 41.2 (35.5–48.9) 54.6 (44.0–65.9) 2,094 12–19 years 19.3 (17.5–21.4) 9.9 (9.5–10.9) 14.4 (12.5–15.7) 19.9 (17.6–21.9) 27.1 (23.6–30.2) 36.5 (28.6–45.6) 42.2 (35.1–52.1) 640 20–39 years 18.7 (17.3–20.1) 8.9 (8.2–10.2) 12.6 (11.2–14.2) 18.7 (17.7–20.4) 27.4 (24.9–29.7) 36.9 (33.6–41.3) 44.3 (38.6–60.8) 490 40–59 years 22.0 (19.7–24.5) 10.6 (9.2–12.3) 15.3 (14.1–18.0) 22.2 (20.2–24.2) 32.2 (27.4–35.4) 43.8 (33.5–62.7) 61.5 (43.8–81.8) 387 ≥ 60 years 23.2 (20.8–25.9) 9.9 (7.7–13.0) 16.6 (15.0–17.9) 23.9 (20.9–27.2) 34.7 (30.0–39.3) 50.3 (40.8–68.9) 69.4 (49.6–90.0) 577 Mexican American 14.7 (13.0–16.6) 7.4 (5.6–7.9) 10.3 (8.3–11.8) 15.9 (13.4–17.9) 21.1 (18.7–23.5) 28.1 (24.1–35.0) 35.5 (28.9–38.5) 485 Non-Hispanic black 21.6 (19.1–24.4) 9.9 (7.5–11.9) 14.8 (12.5–16.8) 22.0 (19.5–24.9) 32.2 (28.1–36.2) 43.8 (37.2–57.3) 57.5 (43.8–78.4) 538 Non-Hispanic white 21.4 (19.9–23.1) 10.5 (9.5–11.5) 15.0 (14.4–16.0) 21.9 (20.5–23.0) 30.2 (27.7–33.0) 41.3 (35.7–49.6) 55.9 (44.0–69.4) 962 Female 18.4 (17.0–20.0) 9.0 (7.8–9.9) 12.4 (11.5–13.8) 18.2 (16.8–19.7) 27.3 (23.6–30.0) 39.7 (34.4–42.6) 45.7 (42.3–61.5) 1,041 Male 23.3 (21.1–25.6) 12.3 (10.4–13.5) 17.7 (15.9–18.9) 23.9 (22.3–25.3) 32.1 (28.7–35.7) 45.3 (35.5–62.7) 62.7 (43.8–81.8) 1,053 Open in a separate window Table 5 Variable Geometric mean 10th percentile 25th percentile 50th percentile 75th percentile 90th percentile 95th percentile No. All 1.0 (0.8–1.1) 0.4 (0.3–0.4) 0.6 (0.5–0.6) 1.0 (0.9–1.1) 1.5 (1.2–1.7) 2.2 (1.6–3.8) 3.2 (1.8–7.7) 2,094 12–19 years 0.9 (0.7–1.0) 0.3 (0.3–0.4) 0.5 (0.5–0.6) 0.7 (0.6–0.9) 1.2 (0.9–1.5) 1.9 (1.2–3.3) 2.7 (1.3–6.3) 640 20–39 years 1.0 (0.8–1.1) 0.3 (0.2–0.5) 0.6 (0.6–0.7) 0.9 (0.8–1.1) 1.4 (1.2–1.7) 2.1 (1.7–2.7) 2.8 (1.9–6.1) 490 40–59 years 1.1 (0.9–1.4) 0.5 (0.4–0.5) 0.7 (0.6–0.7) 1.0 (0.9–1.2) 1.7 (1.2–2.4) 2.7 (1.6–5.9) 4.3 (1.7–9.3) 387 ≥ 60 years 0.8 (0.7–1.0) 0.3 (0.2–0.3) 0.5 (0.5–0.6) 0.9 (0.8–1.0) 1.3 (1.1–1.5) 1.9 (1.5–3.0) 3.0 (1.6–6.5) 577 Mexican American 0.7 (0.6–0.8) 0.2 (0.1–0.2) 0.5 (0.4–0.5) 0.7 (0.5–0.8) 1.0 (0.9–1.3) 1.6 (1.2–1.8) 2.0 (1.6–2.8) 485 Non-Hispanic black 1.1 (0.8–1.5) 0.4 (0.3–0.6) 0.6 (0.5–0.8) 1.0 (0.8–1.4) 1.6 (1.2–2.7) 3.1 (1.5–6.5) 4.7 (2.1–9.3) 538 Non-Hispanic white 1.0 (0.8–1.1) 0.4 (0.3–0.4) 0.5 (0.5–0.6) 0.8 (0.8–0.9) 1.5 (1.2–1.7) 2.2 (1.6–3.4) 2.9 (1.8–6.2) 962 Female 0.9 (0.7–1.0) 0.4 (0.3–0.4) 0.6 (0.5–0.6) 0.9 (0.7–0.9) 1.2 (1.0–1.6) 2.2 (1.4–3.3) 3.0 (1.7–6.1) 1,041 Male 1.1 (0.9–1.3) 0.5 (0.4–0.5) 0.6 (0.6–0.7) 1.0 (0.9–1.2) 1.6 (1.3–1.8) 2.4 (1.7–4.8) 4.0 (1.8–8.7) 1,053 Open in a separate window Statistically significant correlations (p < 0.001) existed between the log-transformed concentrations of PFOS and PFOA (Pearson correlation coefficient r = 0.66), PFHxS (r = 0.56), and PFNA (r = 0.50); between PFOA and PFHxS (r = 0.46) and PFNA (r = 0.55); and between PFHxS and PFNA (r = 0.17). The final models included sex (p < 0.01), age, race/ethnicity, and age-by-race/ethnicity interaction (p = 0.01) for PFOS; sex, race/ethnicity, age, education, sex-by-age (p < 0.01), sex-by-race/ethnicity (p = 0.03), and education-by-age (p = 0.04) interactions for PFOA; sex, race/ethnicity (p = 0.01), age, and sex-by-age interaction (p = 0.02) for PFHxS; and sex (p < 0.01), race/ethnicity, age, education (p = 0.02), smoking status (p = 0.02), and race/ethnicity-by-age (p < 0.01) and age-by-smoking status (p = 0.04) interactions for PFNA. Because of these interactions with age, concentrations were compared at the 25th (age = 26 years), 50th (age = 41 years), 75th (age = 55 years), and 90th (age = 70 years) percentiles of age. LSGM concentrations provide geometric mean estimates for a demographic variable after adjustment for the model covariates ( ). The statistical significance values when comparing these LSGM concentrations are shown in the Supplemental Material, Table S7 (online at http://www.ehponline.org/docs/2007/10598/suppl.pdf). PFOS LSGM concentrations were significantly higher (p < 0.01) in males than in females. Similarly, for PFOA and PFHxS, males had significantly higher LSGM concentrations than females except at the 90th percentile of age ( ). LSGM concentrations of PFHxS were significantly lower for Mexican Americans than for non-Hispanic blacks (p = 0.01) and non-Hispanic whites (p < 0.01); LSGM concentrations did not differ significantly between non-Hispanic whites and non-Hispanic blacks (p = 0.49). PFOS and PFNA LSGM concentrations were significantly lower in Mexican Americans than in non-Hispanic blacks (PFOS, p < 0.01; PFNA, p < 0.01–0.03) and non-Hispanic whites (PFOS, p < 0.01; PFNA, p < 0.01–0.02), regardless of age; LSGM concentrations between non-Hispanic whites and non-Hispanic blacks differed significantly only at the 75th and 90th percentiles of age ( ). Non-Hispanic whites had significantly higher PFOA LSGM concentrations (p < 0.01), regardless of sex, than Mexican Americans. The differences between Mexican-American males and non-Hispanic black males and between non-Hispanic white males and non-Hispanic black males were not statistically significant. Table 6 Group PFOA PFOS PFHxS PFNA Female 18.5 (17.1–20) 0.9 (0.7–1) Male 23.6 (21.8–25.7) 1.1 (0.9–1.3) Female: age P25 3.4 (3.1–3.7) 1.7 (1.5–1.9) Female: age P50 3.5 (3.3–3.8) 1.7 (1.5–1.9) Female: age P75 3.7 (3.4–4) 1.7 (1.5–2) Female: age P90 3.8 (3.4–4.2) 1.7 (1.5–2) Male: age P25 5.1 (4.7–5.5) 2.4 (2–2.8) Male: age P50 4.5 (4.2–4.9) 2.2 (1.9–2.6) Male: age P75 4.1 (3.7–4.5) 2.1 (1.8–2.4) Male: age P90 3.7 (3.2–4.2) 1.9 (1.6–2.3) MA 1.4 (1.1–1.7) NHB 1.9 (1.6–2.3) NHW 2.0 (1.8–2.3) Female, MA 2.6 (2.3–3) Female, NHB 2.8 (2.5–3.2) Female, NHW 3.8 (3.5–4.1) Male, MA 3.6 (3.3–3.9) Male, NHB 4.1 (3.5–4.8) Male, NHW 4.6 (4.2–5.1) MA: age P25 13.9 (12.5–15.5) 0.7 (0.6–0.8) MA: age P50 15.1 (13.6–16.8) 0.7 (0.6–0.8) MA: age P75 16.3 (14.4–18.4) 0.7 (0.5–0.8) MA: age P90 17.7 (15.3–20.6) 0.6 (0.5–0.8) NHW: age P25 20.1 (18.6–21.8) 1 (0.8–1.2) NHW: age P50 21.2 (19.6–22.9) 1 (0.8–1.1) NHW: age P75 22.3 (20.5–24.3) 0.9 (0.8–1.1) NHW: age P90 23.5 (21.3–26) 0.9 (0.8–1) NHB: age P25 19.9 (17.9–22.1) 1.1 (0.8–1.4) NHB: age P50 22.6 (20.1–25.5) 1.2 (0.9–1.6) NHB: age P75 25.5 (22.1–29.5) 1.3 (1–1.9) NHB: age P90 29.0 (24.3–34.7) 1.5 (1–2.1) NonSMK: age P25 1 (0.8–1.1) NonSMK: age P50 1 (0.8–1.1) NonSMK: age P75 1 (0.8–1.1) NonSMK: age P90 1 (0.8–1.2) SMK: age P25 1.1 (0.9–1.3) SMK: age P50 1 (0.8–1.1) SMK: age P75 0.9 (0.8–1) SMK: age P90 0.8 (0.7–1) < HS 0.7 (0.6–0.8) = HS 1 (0.8–1.1) > HS 1.2 (0.9–1.7) < HS: age P25 3.7 (3.4–4.1) < HS: age P50 3.7 (3.4–4.1) < HS: age P75 3.7 (3.3–4.1) < HS: age P90 3.7 (3.3–4.2) = HS: age P25 4.4 (4.1–4.7) = HS: age P50 4 (3.7–4.3) = HS: age P75 3.7 (3.3–4.1) = HS: age P90 3.3 (2.8–4) > HS: age P25 4.2 (3.8–4.6) > HS: age P50 4.1 (3.7–4.5) > HS: age P75 4.1 (3.6–4.6) > HS: age P90 4 (3.4–4.7) Open in a separate window We used a two-sample t-test to compare the difference of the two geometric mean concentrations (on the log scale) of PFOS, PFOA, PFHxS, and PFNA during NHANES 1999–2000 and NHANES 2003–2004 ( ), taking into account their associated standard errors and degrees of freedom, by age, sex, and race/ethnicity, using SAS. The differences were all statistically significant (p < 0.05), except for PFHxS in Mexican Americans (p = 0.21) ( ). We analyzed the NHANES 2003–2004 samples first and then the NHANES 1999–2000 samples (Calafat et al. 2007) using two methods that differed in the manner in which PFCs were extracted and preconcentrated from the serum (Kuklenyik et al. 2004, 2005). In both methods, we used tandem mass spectrometry with 18O 2 -PFOS, 13C 2 -PFOA, and 18O 2 -PFOSA (only for NHANES 1999–2000) for quantification, the same multiple reaction monitoring transitions for quantification for PFOA (413/369) and PFOS (499/99), the same QC materials and analytical standards. 18O 2 -PFOSA was not commercially available when the 2003–2004 NHANES samples were analyzed. Except for PFNA and PFOA, for which the LODs were the same regardless of the method, the method used for NHANES 1999–2000 (Kuklenyik et al. 2005) had slightly lower LODs than the method used for NHANES 2003–2004 (Kuklenyik et al. 2004) ( ). To estimate whether method differences could account for the differences in concentrations, we analyzed QC samples from low and high concentration pools and 124 split samples using both methods. The two methods showed good agreement from the results of the split sample analysis [presented for PFOA in Figures S1 and S2 in Supplemental Material (online at http://www.ehponline.org/docs/2007/10598/suppl.pdf)]. Results were similar for all other analytes (data not shown). In general, analysis of the QC pools showed mean concentrations and coefficients of variation which were similar between the two methods ( ). Table 7 PFOS PFOA PFHxS PFNA Variable 1999–2000 2003–2004 1999–2000 2003–2004 1999–2000 2003–2004 1999–2000 2003–2004 All 30.4 (27.1–33.9) 20.7 (19.2–22.3) 5.2 (4.7–5.7) 3.9 (3.6–4.3) 2.1 (1.9–2.4) 1.9 (1.7–2.2) 0.5 (0.5–0.7) 1.0 (0.8–1.1) 12–19 years 29.1 (26.2–32.4) 19.3 (17.5–21.4) 5.5 (5.0–6.0) 3.9 (3.5–4.4) 2.7 (2.1–3.4) 2.4 (2.1–2.9) 0.5 (0.4–0.5) 0.9 (0.7–1.0) 20–39 years 27.5 (24.9–30.2) 18.7 (17.3–20.1) 5.2 (4.7–5.7) 3.9 (3.6–4.2) 2.0 (1.7–2.3) 1.8 (1.6–2.0) 0.5 (0.4–0.6) 1.0 (0.8–1.1) 40–59 years 33.0 (28.0–38.8) 22.0 (19.7–24.5) 5.4 (4.7–6.2) 4.2 (3.8–4.8) 2.1 (1.8–2.3) 1.9 (1.6–2.2) 0.6 (0.4–0.7) 1.1 (0.9–1.4) ≥ 60 years 33.3 (28.5–38.8) 23.2 (20.8–25.9) 4.8 (4.3–5.5) 3.7 (3.3–4.1) 2.2 (1.9–2.5) 2.0 (1.7–2.4) 0.6 (0.5–0.8) 0.8 (0.7–1.0) Female 28.0 (24.6–31.8) 18.4 (17.0–20.0) 4.8 (4.3–5.3) 3.5 (3.2–3.8) 1.8 (1.6–2.1) 1.7 (1.6–1.9) 0.5 (0.4–0.6) 0.9 (0.7–1.0) Male 33.4 (29.6–37.6) 23.3 (21.1–25.6) 5.7 (5.2–6.3) 4.5 (4.1–4.9) 2.6 (2.3–3.0) 2.2 (1.9–2.5) 0.6 (0.5–0.7) 1.1 (0.9–1.3) Mexican American 22.7 (19.8–25.9) 14.7 (13.0–16.6) 3.9 (3.6–4.2) 3.1 (2.8–3.4) 1.5 (1.1–1.9) 1.4 (1.2–1.7) 0.3 (0.3–0.4) 0.7 (0.6–0.8) Non-Hispanic black 33.0 (26.2–41.6) 21.6 (19.1–24.4) 4.8 (4.1–5.6) 3.4 (3.0–3.8) 2.2 (1.6–2.9) 1.9 (1.6–2.3) 0.8 (0.6–1.0) 1.1 (0.8–1.5) Non-Hispanic white 32.0 (29.1–35.2) 21.4 (19.9–23.1) 5.6 (5.0–6.2) 4.2 (3.9–4.5) 2.3 (2.0–2.5) 2.0 (1.8–2.3) 0.6 (0.5–0.7) 1.0 (0.8–1.1) Open in a separate window

Table 3 Variable Geometric mean 10th percentile 25th percentile 50th percentile 75th percentile 90th percentile 95th percentile No. All 3.9 (3.6–4.3) 1.9 (1.8–2.1) 2.7 (2.6–3.0) 4.0 (3.8–4.4) 5.8 (5.2–6.3) 7.8 (6.7–9.6) 9.8 (7.4–14.1) 2,094 12–19 years 3.9 (3.5–4.4) 2.2 (1.9–2.3) 2.9 (2.6–3.2) 3.9 (3.3–4.4) 5.4 (4.6–6.1) 6.9 (5.6–9.2) 8.6 (5.9–12.6) 640 20–39 years 3.9 (3.6–4.2) 1.8 (1.5–2.1) 2.7 (2.5–3.0) 4.1 (3.7–4.5) 5.8 (5.4–6.1) 7.6 (7.3–8.4) 9.6 (8.4–11.1) 490 40–59 years 4.2 (3.8–4.8) 2.0 (1.8–2.4) 2.9 (2.6–3.2) 4.2 (3.9–4.8) 6.3 (5.3–7.2) 8.2 (6.8–10.7) 10.6 (7.4–16.9) 387 ≥ 60 years 3.7 (3.3–4.1) 1.8 (1.5–2.1) 2.7 (2.4–2.9) 3.9 (3.5–4.3) 5.4 (4.9–5.9) 7.2 (6.0–9.5) 9.5 (6.9–14.1) 577 Mexican American 3.1 (2.8–3.4) 1.4 (1.1–1.8) 2.2 (1.9–2.5) 3.3 (3.0–3.6) 4.4 (4.1–5.1) 6.7 (5.7–7.3) 7.6 (6.7–10.5) 485 Non-Hispanic black 3.4 (3.0–3.8) 1.2 (1.1–1.6) 2.2 (1.9–2.5) 3.7 (3.1–4.2) 5.1 (4.4–6.1) 7.7 (5.3–10.9) 9.3 (6.5–13.9) 538 Non-Hispanic white 4.2 (3.9–4.5) 2.1 (2.0–2.3) 3.0 (2.6–3.2) 4.2 (3.9–4.6) 5.9 (5.4–6.6) 7.8 (7.2–9.1) 9.8 (7.6–13.3) 962 Female 3.5 (3.2–3.8) 1.6 (1.5–1.9) 2.5 (2.2–2.7) 3.6 (3.2–3.9) 5.2 (4.6–5.7) 7.1 (6.3–8.2) 8.4 (7.4–10.6) 1,041 Male 4.5 (4.1–4.9) 2.3 (2.0–2.4) 3.2 (3.1–3.5) 4.6 (4.2–5.0) 6.3 (5.6–7.1) 8.3 (6.8–11.8) 10.4 (7.4–17.5) 1,053 Open in a separate window Table 4 Variable Geometric mean 10th percentile 25th percentile 50th percentile 75th percentile 90th percentile 95th percentile No. All 1.9 (1.7–2.2) 0.7 (0.6–0.7) 1.0 (0.9–1.2) 1.9 (1.6–2.1) 3.3 (2.8–3.9) 5.9 (4.8–7.2) 8.3 (7.1–9.7) 2,094 12–19 years 2.4 (2.1–2.9) 0.6 (0.5–0.8) 1.2 (1.0–1.4) 2.3 (1.7–3.0) 4.8 (3.9–6.0) 9.5 (6.8–12.5) 13.1 (9.9–19.6) 640 20–39 years 1.8 (1.6–2.0) 0.5 (0.5–0.6) 1.0 (0.9–1.2) 1.7 (1.5–2.0) 2.8 (2.5–3.3) 4.8 (3.9–6.1) 6.7 (4.9–9.4) 490 40–59 years 1.9 (1.6–2.2) 0.7 (0.5–0.8) 1.0 (0.9–1.2) 1.6 (1.4–2.0) 3.1 (2.3–4.5) 5.5 (4.3–6.9) 6.7 (5.5–8.2) 387 ≥ 60 years 2.0 (1.7–2.4) 0.8 (0.5–0.9) 1.1 (1.0–1.3) 1.9 (1.6–2.1) 3.2 (2.6–3.7) 7.2 (4.3–9.7) 10.2 (7.0–12.6) 577 Mexican American 1.4 (1.2–1.7) 0.5 (0.3–0.7) 0.7 (0.5–0.9) 1.4 (1.2–1.7) 2.3 (1.9–2.7) 4.2 (3.1–5.1) 5.4 (4.0–8.9) 485 Non-Hispanic black 1.9 (1.6–2.3) 0.5 (0.3–0.7) 1.1 (0.9–1.3) 1.9 (1.5–2.2) 3.4 (2.7–4.3) 6.0 (5.0–7.1) 8.2 (6.3–12.0) 538 Non-Hispanic white 2.0 (1.8–2.3) 0.7 (0.6–0.8) 1.1 (1.0–1.3) 1.9 (1.6–2.1) 3.3 (2.8–4.0) 6.0 (4.6–7.8) 8.1 (6.9–10.1) 962 Female 1.7 (1.6–1.9) 0.6 (0.5–0.6) 0.9 (0.8–1.0) 1.5 (1.4–1.8) 2.9 (2.5–3.5) 5.8 (4.6–6.9) 8.2 (6.7–10.0) 1,041 Male 2.2 (1.9–2.5) 0.8 (0.7–1.0) 1.3 (1.1–1.4) 2.0 (1.8–2.4) 3.3 (2.8–4.4) 6.1 (4.6–8.1) 8.5 (6.4–10.5) 1,053 Open in a separate window

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[1] Url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2072821/

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