Short Communication
Striking association between urinary cadmium level and albuminuria among Torres Strait Islander people with diabetes

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Abstract

Objectives

Indigenous people of the Torres Strait (Australia) have greater potential for cadmium exposure and renal damage than other Australians due to high cadmium in some traditional seafood and a high prevalence of Type 2 diabetes, hypertension, smoking, and obesity. This study explored associations between albuminuria and an index of cadmium exposure (urinary cadmium excretion) in the presence and absence of Type 2 diabetes.

Research design and methods

Two population-based, cross-sectional studies were undertaken in the Torres Strait to obtain data on body mass index (BMI), blood pressure, chronic disease, smoking, urinary cadmium, and albumin creatinine ratio (ACR).

Results

Age- and BMI-adjusted urinary cadmium levels were significantly higher (p<0.01) among people with diabetes and albuminuria (n=22, geometric mean (GM) 1.91 μg Cd/g creatinine) compared to those with diabetes and normal ACR (n=21, GM 0.74 μg Cd/g creatinine). Urinary cadmium was also strongly associated (p<0.001) with ACR among people with diabetes in regression models and remained significant after controlling for age, sex, BMI, smoking status, and hypertension (or continuous systolic and diastolic measurements).

Conclusions

While the study has methodological limitations and the nature of the association is unclear, the striking dose-dependent links between markers of cadmium exposure and of Type 2 diabetic nephropathy highlight the need for further definitive research on the health effects of cadmium in the presence of diabetes.

Introduction

The incidence of chronic diseases has increased alarmingly in recent years (Australian Institute of Health and Welfare, 2005). Like many Indigenous and Oceanic people (Yeates and Tonelli, 2006; Weil and Nelson, 2006), Aboriginal and Torres Strait Islander Australians experience a high prevalence of renal disease associated with Type 2 diabetes and hypertension that contributes to higher mortality and shorter lifespan (Hoy, 1996; Rowley et al., 2000; Queensland Health, 2001; Leonard et al., 2002; McCulloch et al., 2003). This is associated with a high prevalence of many known risk factors, e.g. relative socio-economic disadvantage, high body mass index (BMI), smoking, low micronutrient consumption, high serum cholesterol and triglycerides, and insufficient physical activity (Queensland Health, 2001; Leonard et al., 2002; McCulloch et al., 2003; Cass et al., 2004).

Additional aetiological factors, for example, renal toxins, may contribute to these known risks. Of particular concern for Torres Strait Islanders is cadmium due to high levels in some traditional seafood (Gladstone, 1996; Haynes and Kwan, 2001). Recent studies have found that 12% of urine samples from adult residents (Haswell-Elkins et al., 2007a) and 31.7% from women aged 30–50 years from three Torres Strait Islands (Haswell-Elkins et al., 2007b) contained over 2 μg cadmium/g creatinine.

Urinary cadmium levels are both an indicator of body burden and associated with risk of renal injury (Trevisan et al., 1994; Buchet et al., 1990; Akesson et al., 2005; Satarug et al., 2000a, Satarug et al., 2000b; Jin et al., 1994, Jin et al., 1999; Bernard et al., 1991). Many studies have reported increased tubule and glomerular damage associated with cadmium at levels of 0.8–2 μg/g creatinine, with higher risk among females and people with diabetes (Buchet et al., 1990; Jarup et al., 2000; Satarug et al., 2000b; Akesson et al., 2005; Chen et al., 2006). Experimental studies in a diabetic mouse model have induced glomerulonephropathy with cadmium levels comparable to those found among human populations (Jin et al., 1994, Jin et al., 1999; Bernard et al., 1991). Examination of NHANES data (Schwartz et al., 2003) suggested an increased risk of diabetes linked to urinary cadmium >1.0 μg/g creatinine.

Despite these findings, the contribution of cadmium to diabetes and diabetic nephropathy remains unclear and its potential role is often overlooked in research studies on kidney disease. This project utilised data collected from two community-based studies conducted in 1996 and 2003 (Haswell-Elkins et al., 2007a, Haswell-Elkins et al., 2007b) to explore associations between urinary cadmium and albuminuria in the Torres Strait.

Section snippets

Sampling strategy

The samples and data examined in this study were collected from three different Torres Strait Islands that had typical chronic disease profiles in relation to diabetes and elevated albuminuria in the region. Consultations were conducted with the Torres Strait and Northern Peninsula Area Health Council, District Health Service and Community Councils. Approval was granted by the University of Queensland Human Ethics Committee.

The methodology of the 1996 study is detailed elsewhere (Haswell-Elkins

Results

The total 182 participants included 124 women and 58 men (see Table 1 for details). Forty-three (23.6%) had diabetes, 42 (23.1%) were hypertensive, and 42 (23.1%) had albuminuria (ACR⩾3.4). Ninety-three percent had a BMI>25, and 41.9% of women and 44.8% of men were current smokers.

Cadmium increased significantly with age (B=0.016, S.E. 0.002, p<0.001) and was higher among women (B=0.169, S.E. 0.059, p=0.005) and current smokers (B=0.136, S.E. 0.051, p=0.008) (adjusted r2=0.31), but did not vary

Discussion and conclusion

This small but unique population-based study explored relationships between urinary cadmium, Type 2 diabetes, and abnormally increased urinary albumin excretion (albuminuria), a known marker for glomerular dysfunction and an independent risk factor for end-stage renal failure, cardiovascular disease and mortality (Hoy, 1996; Rowley et al., 2000; Hoy et al., 2001; Mattock et al., 1992). Although cadmium has long been suspected to potentiate diabetic nephropathy, few studies have focused

Conflict of interest

None of the authors have any potential conflicts of interest in this research. The study received ethical approval from the Human Ethics Research Committees of the University of Queensland.

Acknowledgments

This research was funded in part by a grant from the Australian Institute for Aboriginal and Torres Strait Islander Studies, Canberra. We thank the Torres Strait and Northern Peninsula Area Health Council and District, the District Manager Mr. Phillip Mills and the participants and the Island Community Council for interest and support.

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