Recommended Rice Intake Levels Based on Average Daily Dose and Urinary Excretion of Cadmium in a Cadmium-Contaminated Area of Northwestern Thailand

This study was performed to investigate the dose-response relationship between average daily cadmium dose (ADCD) from rice and the occurrence of urinary cadmium (U-Cd) in individuals eating that rice. This was a retrospective cohort designed to compare populations from two areas with different levels of cadmium contamination. Five-hundred and sixty-seven participants aged 18 years or older were interviewed to estimate their rice intake, and were assessed for U-Cd. The sources of consumed rice were sampled for cadmium measurement, from which the ADCD was estimated. Binary logistic regression was used to examine the association between ADCD and U-Cd (cut-off point at 2 μg/g creatinine), and a correlation between them was established. The lowest estimate was ADCD = 0.5 μg/kg bw/day [odds ratio (OR) = 1.71; with a 95% confidence interval (CI) 1.02–2.87]. For comparison, the relationship in the contaminated area is expressed by ADCD = 0.7 μg/kg bw/day, OR = 1.84; [95 % CI, 1.06–3.19], while no relationship was found in the non-contaminated area, meaning that the highest level at which this relationship does not exist is ADCD = 0.6 μg/kg bw/day [95% CI, 0.99–2.95]. Rice, as a main staple food, is the most likely source of dietary cadmium. Abstaining from or limiting rice consumption, therefore, will increase the likelihood of maintaining U-Cd within the normal range. As the recommended maximum ADCD is not to exceed 0.6 μg/kg bw/day, the consumption of rice grown in cadmium-contaminated areas should not be more than 246.8 g/day. However, the exclusion of many edible plants grown in the contaminated area from the analysis might result in an estimated ADCD that does not reflect the true level of cadmium exposure among local people.