Association of cadmium in urine and blood with age in a general population with low environmental exposure

• Lifetime variation of urinary Cd is similar to kidney Cd, after appropriate adjustment.
• Urinary Cd is significantly affected by blood Cd and urinary creatinine.
• Urinary Cd and blood Cd were not significantly higher in former smokers than never smokers.

A recent study reported a nonlinear and nonmonotonic relationship between urinary cadmium (U-Cd) and age and questioned the long-held view that U-Cd is a reliable biomarker of Cd body burden at low exposure levels. In order to reassess the significance of U-Cd as biomarker of Cd body burden, we studied the lifetime trend of U-Cd as functions of diuresis in a cross-sectional study. Cadmium was measured with an inductively coupled plasma mass spectrometer (ICP-MS) for the general population taking part in the Metals and Health Survey in Jiangsu (MHSJ), China, with ages ranging from 2.8 to 86.8 years (n = 1235). Variations in U-Cd and B-Cd with age were modeled using natural cubic splines. Factors associated with U-Cd were analyzed with Pearson correlation and linear regression models. As results, nonsmoking men had peak U-Cd at approximately 60 years, after which it decreased. In nonsmoking women, U-Cd increased from 2.8 years to 50 years, then leveled off. In both genders, B-Cd increased from birth to approximately 30 years and then leveled off. U-Cd, expressed in per liter, was consistently associated with B-Cd and U-creatinine, regardless of smoking status. U-Cd and B-Cd were not significantly higher in former smokers than never smokers. Our study suggests that individual U-Cd level are correlated with B-Cd and U-creatinine, and needed to be appropriately adjusted for B-Cd and U-creatinine, when it is used for a biomarker of kidney burden of Cd.