Positive relationship between mortality from Alzheimer's disease and soil metal concentration in mainland China

An imbalance of metal ions is implicated in the development of Alzheimer's disease (AD). We investigated the relationship between the annual mortality of AD and ionic concentration (iron, zinc, copper, and aluminum) in the soil in mainland China. The AD annual mortality data were from 26 provinces and 3 municipal districts within mainland China between the years 1991 and 2000 and provided by the National Death Cause Surveillance Database of China. The ionic concentration in soil was provided by the China State Environmental Protection Bureau, which was published in 1990. The results showed that the relative risk of mortality in the regions with the highest copper concentrations (60-80 mg/kg) reached 2.634 (95% CI: 2.626-2.642) compared with the regions that had the lowest copper concentrations. The relative risk was 1.292 (95% CI: 1.290-1.294) and 1.248 (95% CI: 1.245-1.251) when the soil iron concentrations exceeded 3 mg/kg and 4 mg/kg, respectively. When the soil zinc concentration was over 100 mg/kg and 200 mg/kg, the relative risk was 1.870 (95% CI: 1.859-1.881) and 2.289 (95% CI: 2.276-2.304), respectively. However, the relative risk was 0.560 (95% CI: 0.559-0.561), 0.604 (95% CI: 0.603-0.605), and 0.267 (95% CI: 0.265-0.268) when the soil aluminum concentration was over 6 mg/kg, 7 mg/kg, and 8 mg/kg, respectively. This study suggests that high concentrations of iron and copper in the soil might be associated with the high AD annual mortality in this region in China, while aluminum had no association with AD mortality.