Cadmium blood and urine concentrations as measures of exposure: NHANES 1999-2010

Abstract

Exposure to cadmium, a heavy metal present in cigarettes, can be assessed in both urine and blood. Few studies have compared the properties of concurrent measurements of urine cadmium (uCd) and blood cadmium (bCd) in relation to the duration and timing of a known exposure. In this study, bCd and uCd were modeled with data from the National Health and Nutrition Examination Survey (1999-2010). Adjusted geometric mean bCd and uCd were estimated from regression results. Each 1% higher geometric mean uCd was associated with 0.50% (95% confidence interval: 0.47%-0.54%; R(2)=0.30) higher bCd. In male never-smokers, bCd was 69% (59%-81%) and uCd was 200% (166%-234%) higher at age ≥70 years versus 20-29 years. Ten pack-years (py) of smoking were associated with 13.7% (10.0%-17.4%) higher bCd and 16.8% (12.6%-21.1%) higher uCd in male smokers. The first year after smoking cessation was associated with 53% (48%-58%) lower bCd and 23% (14%-33%) lower uCd in representative males aged 55 years with 20 py smoking. Smoking in the previous 5 days was associated with 55% (40%-71%) higher bCd and 7% (-3%-18%) higher uCd. Results were similar for women. uCd mainly measures long-term exposure and bCd recent exposure, but with noticeable overlap. Epidemiological studies should base the choice of uCd or bCd on the timing of cadmium exposure relevant to the disease under study.

Figure 1

Blood cadmium and urine cadmium (creatinine corrected) by smoking status and sex (circles: men; triangles: women) with weighted linear regression fit (solid: men; dashed: women). A single outlier, a female never-smoker with uCd 282.9 μg/g-cr. was omitted from plot for clarity and to maximize use of space.

Figure 2

Predicted representative geometric mean urine cadmium (left) and blood cadmium (right), normalized to never-smokers age 20–29 for each sex, within age groups in men (circles) and women (triangles) and smoking status as of NHANES interview date (solid lines: never smokers; dashed lines: former smokers; dotted lines: current smokers). Displayed means illustrate predictions for individuals with BMI 27 kg/m², some college education, non-Hispanic white ethnicity, and urine creatinine 100 mg/dL (urine cadmium only). Age, smoking duration, rate, and time since cessation are set to the mean for each age and smoking group. Error bars represent 95% confidence intervals.

Figure 3

Predicted representative geometric mean urine and blood cadmium among current (dotted lines) and former (dashed lines) smokers, by sex (men: circles, women: triangles). Values are normalized to never-smokers (smoking dose plots) or current smokers (cessation plots) for each sex. uCd and bCd adjusted to BMI of 27 kg/m², non-Hispanic white participants, age 55 years, some college education; and urine creatinine 100 mg/dl (uCd only). Smoking dose was fixed at 20 py in plot of cessation time. Solid horizontal lines show mean values in never smokers (women: upper lines, men: lower lines). Error bars represent 95% confidence intervals.