Letter and Reply Lead and CKD

Sir, We have read with interest the article by Spector et al. [1] which showed that higher blood levels of lead were associated with lower estimated glomerular filtration rate (eGFR) levels and impaired kidney function (eGFR < 60 mL/min/1.73m) in 3941 US adults participating in National Health and Nutrition Examination Survey (NHANES). This effect was particularly observed in subjects >60 years of age. We have recently performed an analysis to assess the relationship between exposure to background environmental lead concentrations and kidney function. To that end, data of individuals who participated in the Prevention of Renal and Vascular Endstage Disease (PREVEND) study, a prospective community-based cohort study, were used [2]. Topsoil lead concentration in the area of residence was used as a marker of environmental lead exposure. Measurement of topsoil lead was commissioned by the Groningen municipal council and performed prior to this study [3]. The end points for kidney function were estimated glomerular filtration rate (eGFR) [4] and decline of eGFR. The relationships between environmental lead exposure (expressed as milligram per kilogram topsoil) and eGFR (in mL/min/ 1.73m) and kidney function decline were assessed using linear regression analyses and adjusted for age, sex, smoking habits and baseline eGFR. All topsoil lead concentrations were well below the Dutch soil concentration limit (intervention value) for lead [mean (SD) lead 38.5 (28.5) mg/kg topsoil). Lead concentrations were available for 8549 of the 8592 participants of the PREVEND study [49.9% male, mean (SD) age 49.8 (12.7) years, 95.5% Caucasian]. Mean eGFR at baseline was 80.6 mL/ min/1.73m and mean yearly decline in eGFR was −0.45 mL/ min/1.73m/year. After adjustment, lead in environmental topsoil was not associated with level of eGFR [an hazard ratio (HR) 0.00 (−0.011 to 0.012)]. The association between environmental lead exposure and yearly decline in kidney function was not clinically relevant, although statistically significant [an HR 0.003 (0.002 to 0.005)]. Similar conclusions were reached when we confined our analyses to subjects >60 years of age. Therefore, we conclude that environmental exposure to background concentrations of lead is not a risk factor for reduced eGFR or accelerated decline in eGFR. These data, in combination with the NHANES data, may indicate that other environmental sources of lead, such as cigarette smoke, lead paint and industrial exposure, may be more important contributors to high-blood levels of lead, leading to reduced glomerular filtration rate [1].