Associations between Urinary Excretion of Cadmium and Proteins in a Nonsmoking Population: Renal Toxicity or Normal Physiology?
Magnus Akerstrom,1 Gerd Sallsten,1 Thomas Lundh,2 and Lars Barregard1
1Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital and University of Gothenburg, Gothenburg, Sweden; 2Department of Occupational and Environmental Medicine, Lund University Hospital, Lund, Sweden
Background: Associations between cadmium (Cd) and kidney function have been reported even at low levels of exposure in the general population. Recently, the causality of these associations has been questioned.
Objectives: We examined associations between urinary Cd (U-Cd; a biomarker of exposure) and urinary proteins that are used as biomarkers of kidney effects, based on repeated short-term sampling in healthy subjects.
Methods: Twenty-four hour urine samples were collected on 2 separate days at six fixed times from 30 healthy nonsmoking men and women (median age 39 years). We analyzed the samples (N = 354) for Cd (i.e., U-Cd) and two proteins used as kidney function biomarkers: urinary albumin (U-Alb) and alpha-1-microglobulin (U-A1M). Concentrations were adjusted for creatinine concentration or for specific gravity, and excretion rates (mass per hour) were calculated. Possible associations were assessed within each individual participant, and mean correlations and regressions were evaluated.
Results: We found clear positive mean associations within individuals between the excretion of U-Cd [mean, 0.11 µg/g creatinine (range, 0.01–0.52 µg/g creatinine)] and both U-Alb and U-A1M. The associations were stronger for excretion rates and concentrations adjusted for specific gravity than for concentrations adjusted for creatinine. We also found significant positive associations of urinary flow with excretion of U-Cd, U-Alb, and U-A1M.
Conclusions: Associations between short-term changes in U-Cd and markers of kidney function within individual nonsmoking study participants are unlikely to reflect effects of Cd toxicity. A more likely explanation is that these associations result from normal variation in renal function, including changes in urinary flow, that influence the urinary excretion of both Cd and proteins in the same direction. These effects of normal variability may result in overestimation of the adverse effects of Cd on kidney function at low-level Cd exposure.
Key words: albumin, alpha-1-microglobulin, cadmium, cadmium toxicity, kidney effect, renal function, urinary excretion.
Environ Health Perspect 121:187–191 (2013). http://dx.doi.org/10.1289/ehp.1205418 [Online 31 October 2012]
Address correspondence to M. Akerstrom, Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital and Academy, University of Gothenburg, PO Box 414, SE-405 30 Gothenburg, Sweden. Telephone: 46 31 786 28 43. E-mail: email@example.com
We thank L. Samuelsson and C. Johansson for help with the data collection.
This work was funded by the Graduate School in Environment and Health, a cooperation between University of Gothenburg (Gothenburg, Sweden), Chalmers University of Technology (Gothenburg, Sweden), and the Västra Götaland Region (Västra Götaland County, Sweden), coordinated by the Centre for Environment and Sustainability (GMV) (Gothenburg, Sweden).
The authors declare they have no actual or potential competing financial interests.
Received 3 May 2012; Accepted 31 October 2012; Online 31 October 2012.
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