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ObjectivesThe inherent nature of the Korean National Health and Nutrition Examination Survey (KNHANES) design requires special analysis by incorporating sample weights, stratification, and clustering not used in ordinary statistical procedures.MethodsThis study investigated the proportion of research papers that have used an appropriate statistical methodology out of the research papers analyzing the KNHANES cited in the PubMed online system from 2007 to 2012. We also compared differences in mean and regression estimates between the ordinary statistical data analyses without sampling weight and design-based data analyses using the KNHANES 2008 to 2010.ResultsOf the 247 research articles cited in PubMed, only 19.8% of all articles used survey design analysis, compared with 80.2% of articles that used ordinary statistical analysis, treating KNHANES data as if it were collected using a simple random sampling method. Means and standard errors differed between the ordinary statistical data analyses and design-based analyses, and the standard errors in the design-based analyses tended to be larger than those in the ordinary statistical data analyses.ConclusionsIgnoring complex survey design can result in biased estimates and overstated significance levels. Sample weights, stratification, and clustering of the design must be incorporated into analyses to ensure the development of appropriate estimates and standard errors of these estimates.

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Objectives-Low-level cadmium exposure, e.g., urinary cadmium < 2.0 μg/g creatinine, is widespread; recent data suggest nephrotoxicity even at these lower levels. Few studies have examined the impact of low-level cadmium exposure in workers who are occupationally exposed to other nephrotoxicants such as lead.Methods-We evaluated associations of urine cadmium, a measure of cumulative dose, with four glomerular filtration measures and N-acetyl-β-D-glucosaminidase (NAG) in lead workers. Recent and cumulative lead dose was assessed via blood and tibia lead, respectively.Results-In 712 lead workers, mean (SD) blood and tibia lead, urine cadmium, and estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease equation were 23.1 (14.1) μg/dl, 26.6 (28.9) μg Pb/g bone mineral, 1.15 (0.66) μg/g creatinine, and 97.4 (19.2) ml/min/1.73m 2 , respectively. After adjustment for age, sex, body mass index, urine creatinine, smoking, alcohol, education, annual income, diastolic blood pressure, current or former lead worker job status, new or returning study participant, and blood and tibia lead, higher ln-urine cadmium was associated with higher calculated creatinine clearance, eGFR (β = 8.7 ml/min/1.73 m 2 ; 95% CI = 5.4, 12.1) and ln-NAG but lower serum creatinine.Conclusions-Potential explanations for these results include a normal physiologic response in which urine cadmium levels reflect renal filtration; the impact of adjustment for urine dilution with creatinine in models of kidney outcomes; and cadmium-related hyperfiltration.

We examined the association of blood pressure with blood levels of cadmium, lead, and their combination in a representative sample of adults from South Korea (Korean National Health and Nutrition Examination Survey, 2008-2013). This cross-sectional study enrolled subjects who were at least 19 years-old, completed a health examination survey, and had blood measurements of lead and cadmium. We estimated the adjusted mean differences in diastolic and systolic blood pressure associated with doubling of blood lead and cadmium by regression of blood pressure against log-transformed blood metals and their tertiles after covariate adjustment. Adjusted odds ratios for hypertension and prehypertension were calculated for log-transformed blood levels of lead and cadmium and their tertiles. In the general population of Korea, blood lead level was associated with increased BP and risk of hypertension. Blood cadmium levels had a stronger association with elevated blood pressure and risk of hypertension than blood lead levels, and these associations remained significant after statistical adjustment for blood lead. The combination of blood lead and cadmium was more strongly associated with elevated blood pressure than exposure to each individual metal. In females, there was a stronger relationship between blood pressure and blood levels of these metals by analyzing interaction model. After adjustment for confounding factors, there were significant associations of blood pressure with the level of blood lead, cadmium, and their combination in adults from South Korea.