Table 1.

Urine cadmium levels over time by participant characteristics.^a,b

Urine cadmium, geometric mean (µg/g)					Percent reduction of geometric mean (CI)c
					1999–2002 vs. 1988–1994	2003–2008 vs. 1988–1994
Characteristic	n	1988–1994	1999–2002	2003–2008
Overall		19,759		0.37		0.27		0.24		27.8 (22.3, 32.9)		34.3 (29.9, 38.4)
Age group (years)
< 35		5,676		0.2		0.15		0.14		23.0 (14.9, 30.3)		30.5 (23.7, 36.8)
35–50		5,231		0.36		0.27		0.25		25.0 (16.0, 33.0)		32.2 (25.2, 38.6)
50–65		4,045		0.6		0.41		0.37		31.9 (24.1, 38.9)		38.8 (33.3, 43.8)
≥ 65		4,807		0.69		0.44		0.44		35.5 (30.3, 40.2)		35.6 (30.4, 40.4)
Sex
Men		9,360		0.31		0.22		0.21		29.0 (22.8, 34.7)		33.5 (28.5, 38.1)
Women		10,399		0.44		0.32		0.28		26.7 (20.3, 32.6)		35.0 (29.9, 39.7)
Race/ethnicity
White		8,734		0.36		0.26		0.24		27.5 (20.3, 34.0)		33.2 (27.4, 38.5)
African American		4,830		0.41		0.27		0.24		35.1 (26.1, 43.1)		42.2 (38.2, 46.0)
Mexican American		5,061		0.38		0.29		0.26		23.2 (14.7, 30.9)		32.8 (27.2, 37.9)
Other		1,134		0.44		0.33		0.29		25.3 (13.0, 35.8)		34.3 (23.6, 43.5)
Education
≥ High school		12,485		0.35		0.26		0.24		26.7 (20.6, 32.3)		32.1 (27.2, 36.6)
< High school		7,274		0.46		0.33		0.29		28.7 (21.6, 35.2)		37.1 (31.7, 42.0)
BMI (kg/m2)
< 25		7,217		0.38		0.31		0.27		19.3 (8.8, 28.5)		28.8 (21.9, 35.2)
25–30		6,996		0.38		0.26		0.24		31.4 (24.7, 37.4)		35.0 (28.8, 40.7)
≥ 30		5,546		0.35		0.24		0.22		30.9 (24.4, 36.9)		37.4 (32.7, 41.8)
Smoking
Never		10,107		0.27		0.21		0.19		22.1 (15.4, 28.4)		28.4 (22.7, 33.8)
Former		4,524		0.38		0.27		0.25		29.8 (22.3, 36.5)		35.7 (29.8, 41.0)
Current		5,128		0.6		0.47		0.41		22.2 (13.7, 29.9)		32.4 (26.4, 37.8)
Pack-years
0		10,177		0.26		0.21		0.19		21.1 (14.5, 27.1)		27.0 (21.3, 32.3)
0–10		4,075		0.34		0.28		0.23		16.6 (5.8, 26.2)		31.2 (24.5, 37.3)
10–20		1,803		0.51		0.37		0.34		26.3 (14.8, 36.3)		32.5 (24.3, 39.9)
> 20		3,704		0.71		0.5		0.49		29.8 (23.1, 36.0)		31.4 (25.7, 36.8)
Serum cotinine (ng/mL)
< 0.05		4,578		0.25		0.22		0.2		13.3 (3.0, 22.5)		20.3 (11.1, 28.6)
0.05–10		10,328		0.32		0.24		0.22		25.3 (17.9, 32.1)		31.0 (25.5, 36.2)
10–200		2,062		0.45		0.4		0.34		11.3 (–1.8, 22.7)		24.2 (14.1, 33.1)
≥ 200		2,791		0.76		0.57		0.47		24.1 (15.0, 32.3)		38.2 (32.5, 43.3)
Duration of longest cadmium-associated occupation (years)d
0		17,480		0.36		0.26		0.25		26.9 (21.0, 32.3)		30.1 (24.1, 35.6)
0–10		3,904		0.43		0.32		0.33		27.1 (9.3, 41.3)		23.9 (11.1, 34.9)
10–20		3,476		0.47		0.35		0.35		26.2 (4.3, 43.1)		26.2 (0.5, 45.2)
> 20		3,578		0.51		0.34		0.31		33.5 (15.4, 47.8)		39.7 (23.7, 52.4)
aGeometric means and percent reductions in geometric means were adjusted for age (years modeled as restricted cubic splines with 5 knots), sex (men, women), and race/ethnicity (white, African American, Mexican American, and other). Geometric means were further recalibrated to overall mean. bp-Trend was < 0.001 overall and for all subgroups. cWe obtained adjusted ratios of geometric means comparing survey phase groups (NHANES 1999–2002 and 2003–2008) with respect to the reference survey phase group (NHANES 1988–1994) by exponentiating linear combinations of β-coefficients from regression models with log-transformed cadmium as the dependent variable and survey phase group and confounder factors as interacting independent variables. Subsequently, the percent reduction of the geometric mean was estimated as (1 – ratio of geometric mean) × 100. For instance, a 28.7% reduction comparing urine cadmium concentrations in NHANES 1999–2002 to NHANES 1988–1994 corresponded to a ratio of geometric means comparing NHANES 1999–2002 with NHANES 1988–1994 equal to 0.713. p-Trends comparing 1999–2002 and 2003–2008 with 1988–1994 were obtained using the Wald test. dOccupation variables were only available through 2004.