Iron Trace Elements Concentration in PM10 and Alzheimer's Disease in Lima, Peru: Ecological Study

Abstract

Alzheimer's disease (AD) has been linked to air pollution, especially particulate matter (PM). PM comprises various elements, including iron-rich particles that may reach the brain through inhalation. Lima, Peru is one of the most polluted cities in Latin America, with a high rate of AD. The study aims to evaluate the association between iron (Fe) trace elements in PM₁₀ and AD cases in Lima, Peru. This retrospective ecological study used monthly Fe concentration data from the Peruvian Ministry of Health. AD cases (ICD-10-G30) and dementia in AD cases (DAD, ICD-10-F00) were obtained from the Peruvian CDC. Fe trace element data were available for six districts in Lima for the years 2017-2019 and 2022. Cases were standardized based on ≥60-year-old populations of each district. Hierarchical mixed-effects models of Gaussian and negative binomial families were constructed to evaluate both outcomes jointly (AD + DAD) and separately (AD, and DAD). A sensitivity analysis was conducted by excluding data from Lima's downtown district. In the complete model, log-Fe concentration was associated with a higher rate of AD + DAD and DAD, and with a higher IRR for the three outcomes. After controlling for other metals, a higher DAD rate was observed (β-coeff = 6.76, 95%CI 0.07; 13.46, p = 0.048), and a higher IRR for AD + DAD (1.55, 95%CI 1.09; 2.20, p = 0.014) and DAD (1.83, 95%CI 1.21; 2.78, p = 0.004). The association was not significant in the sensitivity analysis. In conclusion, exposure to Fe through PM₁₀ inhalation may be associated with the presence of AD in Lima.

Keywords: Alzheimer’s disease; Latin America; air pollution; iron; particulate matter.

Figure 1

Pearson correlation analysis of the different trace metals in PM₁₀ and Alzheimer’s disease (AD), dementia in Alzheimer’s disease (DAD), and AD + DAD including all the districts (A) and excluding Lima Downtown (B). Pearson coefficient (r) value is inside colored boxes. Colors closer to red mean a more positive correlation, while blue shades indicate a less positive correlation, and a color closer to solid blue means a more negative correlation. For (A), the correlation of AD + DAD with Li, Pb, Zn, Be and Cu was statistically significant (p < 0.05). The correlation of AD with Ni, Se, Mo, and Fe was statistically significant (p < 0.05). The correlation of DAD with Fe, Mn, Li, and Cu was statistically significant (p < 0.05). The correlation of Fe with Cd, Li, Ni, Sb, Pb, Zn, Cu, Mn, Cr, and Se was statistically significant (p < 0.05). For (B), the correlation of AD + DAD with Li, Se, Mn, and Fe was statistically significant (p < 0.05). The correlation of AD with Mo and Fe was statistically significant (p < 0.05). The correlation of DAD with Fe, Mn, and Cu was statistically significant (p < 0.05). The correlation of Fe with Cd, Li, Ni, Sb, Pb, Zn, Cu, Se, Cr, and Mn was statistically significant (p < 0.05).

Figure 2

Scatter plots between Alzheimer’s disease (AD) cases (A), dementia in Alzheimer’s disease (DAD) cases (B), and DAD + AD cases (C) and iron (ng/m³) in PM₁₀ considering all the districts, and excluding Lima Downtown data ((D–F) respectively). The red line represents a perfect linear relationship between the outcomes and Fe concentration.