Cadmium intake and chronic kidney disease: Response to Kawada T

We would like to thank Dr Kawada for the interest in our study. Dr Kawada raised a critical point regarding the provisional tolerable monthly intake (PTMI) for cadmium (25 μg/kg body weight/month) proposed by WHO in 2013 [1]. We agree that the mean dietary cadmium intake in our sample is well below this PTMI. Several other studies in China also found that the mean dietary cadmium was below the PTMI, including Song et al's which found the mean cadmium intake to be 15.3 g/kg BW (compared to 13.6 g/kg BW in our study), and concluded that the health risk from dietary cadmium exposure of the general Chinese people was low [2], [3]. Such a conclusion may be risky from a public health perspective, as it suggests that there is no urgent need to intervene. However, the European Food Safety Authority (EFSA) set a more conservative provisional tolerable weekly intake for cadmium at 2.5 μg/kg BW/week [4]. We found that 65.4% of our participants had an estimated usual cadmium intake above the EFSA TWI, while 2.9% were above the WHO PTMI. The strong association between dietary cadmium intake and chronic kidney disease (CKD) in our study should serve as an alarming signal for public health intervention and further investigation to determine which tolerable limit is more clinically relevant. Our findings provide support for the use of the more conservative EFSA TWI, rather than the PTMI set by WHO, while acknowledging that both figures are provisional. Our findings add additional observational evidence to the previous research summarized by Byber et al[5]. Although we did not have information on the biomarkers of renal tubular damage, several recent studies in China confirmed that cadmium exposure was adversely associated with renal biomarkers, such as N-acetyl-beta-d-glucosamidase [6], [7]. Further longitudinal studies on cadmium exposure and kidney function decline or the development of CKD are needed. The 2015 China Health and Nutrition Survey may provide further opportunity as it will collect follow-up data on kidney function.