Associations between disorders in activities of daily living and heavy metal concentrations in elderly people

Background Heavy metals may play an important role in environmental risk factors associated disorders of activities of daily living (ADL) in older adults.

Objective To investigate the associations between plasma levels of six heavy metals (zinc, arsenic, cadmium, lead, manganese, and copper) and ADL disorders in older adults.

Methods A cross-sectional survey was conducted from 2018 to 2019 among 1412 rural elderly people in Gongcheng Yao Autonomous County, Guangxi Zhuang Autonomous Region. The plasma metal concentrations were detected by inductively coupled plasma mass spectrometry (ICP-MS), and subsequently classified into three groups (T1-T3) based on tertiles, with the T1 group as the reference. The samples were assessed for ADL disorders using the ADL scale. Logistic regression and restricted cubic spline model (RCS) were used to estimate the odds ratio (OR) and 95% confidence interval (CI) to assess the associations between heavy metals and the prevalence of reporting ADL disorders.

Results The mean age of the study population was (68.52 ± 5.92) years, 825 (58.4%) female and 587 (41.6%) male. Of these, 372 (26.34%) subjects reported ADL disorders, and most of them were female (74.30%). The results of logistic regression showed that the participants in the cadmium T2 group (0.15-0.25 µg·L⁻¹) had a higher risk of ADL disorders compared to the T1 group (≤0.15 μg·L⁻¹) (OR=1.552, 95%CI: 1.086, 2.134). After stratification by sex, the relative risk of ADL disorders was lower in the plasma copper T3 group (>1019.58 µg·L⁻¹) compared to the T1 group (≤868.12 μg·L⁻¹) in men (OR=0.481, 95%CI: 0.232, 0.998). The relative risk of ADL disorders was higher in the plasma cadmium T2 group (0.15-0.25 µg·L⁻¹) compared to the T1 group (≤0.15 μg·L⁻¹) in women (OR=1.758, 95%CI: 1.182, 2.616). The RCS results showed that the risk of ADL disorders in men was nonlinearly associated with copper (P_nonlinear=0.011, P_overall<0.05).

Conclusion High levels of cadmium are positively associated with the risk of reporting ADL disorders, while high levels of copper are negatively associated with the risk of reporting ADL disorders in men.