Occupational Exposure to Aluminum and Alzheimer Disease

Abstract

Objective:We conducted a meta-analysis to systematically quantify the association between occupational exposure to aluminum and risk of Alzheimer disease (AD). Methods: Electronic database searches were conducted up to March 2015 for controlled studies. Study quality was assessed using the Newcastle-Ottawa Scale. Results: Three retrospective case-control studies, involving 1056 participants, met the criteria for inclusion. All studies used surrogate informants to ascertain exposure. Occupational aluminum exposure was not associated with AD (odds ratio, 1.00; 95% confidence interval, 0.59 to 1.68), even in sensitivity analysis excluding studies with low-quality assessment scores (odds ratio, 1.06; 95% confidence interval, 0.36 to 3.10). Conclusions:The findings of the present meta-analysis do not support a causative role of aluminum in the pathogenesis of AD. Nevertheless, in the absence of prospective studies with more precise ascertainment of exposure, a role for aluminum cannot be definitively excluded.A lzheimer disease (AD) accounts for 60% to 80% of dementia cases. 1 The worldwide prevalence of AD is projected to exceed 100 million by 2050, by which time 1 in 85 persons is expected to be living with this debilitating disease. 1 As current treatments for AD are unable to significantly modify disease progression, there has been growing interest in the identification of risk factors that may enable implementation of preventative strategies.Pathologically, AD is characterized by the aggregation of β-amyloid peptide in the form of neuritic plaques and the accumulation of hyperphosphorylated tau proteins as neurofibrillary tangles. 2 Nevertheless, a complete understanding of the mechanisms and factors underlying these changes remains elusive. Although AD is known to have a genetic component, epidemiological studies show more than two thirds of identical twins are discordant, indicating a significant etiological role for environmental factors. 3 Occupational exposures have garnered particular interest as the long prodromal phase of AD suggests the gradual effect or accumulation of a neurotoxin over many years. Previous meta-analyses have demonstrated an increased risk of AD with occupational exposure to low-frequency electromagnetic fields, 4 but no association with lead or industrial solvents. 5 Nevertheless, to date, the relationship between occupational exposure to aluminum and the risk of AD has not been systematically quantified.Aluminum is the most abundant metal in the Earth's crust, but the daily human intake in most countries is only in the order of a few milligrams. 6 Nevertheless, in individuals working in aluminumrelated industries, absorption from the nasal cavity may represent a significant additional source of aluminum exposure. 6 Olfactory neuron terminals within the nasal mucosa represents the only site where the central nervous system is directly exposed to the environment and inhalation of aluminum has been shown to markedly increase brain aluminum levels. 7 The present meta-analysis was thus con...

Multi-Elemental Analysis of Human Optic Chiasm—A New Perspective to Reveal the Pathomechanism of Nerve Fibers’ Degeneration

“…Al has been shown to be particularly dangerous for the functioning of the central nervous system, causing cognitive and neurodegenerative disorders. Many studies have shown that exposure to Al can cause neuropsychiatric and neurological symptoms, as well as diseases such as Alzheimer’s disease, risk of cognitive impairment, dementia, allergic conditions, inflammatory skin lesions, and a higher risk of developing lung cancer or bladder cancer [ 64 , 65 , 66 , 67 ]. Yoshimasu et al found higher concentrations of Al in the brain of victims of amyotrophic lateral sclerosis (ALS) [ 67 ].…”

Circulatory Levels of Toxic Metals (Aluminum, Cadmium, Mercury, Lead) in Patients with Alzheimer’s Disease: A Quantitative Meta-Analysis and Systematic Review

“…For example, several studies have observed higher levels of Al in the circulation of AD patients [16][17][18][19][20][21][22][23], whereas B. Bobba reported lower levels of Al in serum (p < 0.05) [24], and other studies demonstrated no significance of Al level between AD and control [25,26]. Moreover, several meta-analyses of Al reported inconsistent results [27][28][29]. In addition, only a few of studies reported significant changes in the levels of Hg, Pb, and Cd.…”

The Mediation Effects of Aluminum in Plasma and Dipeptidyl Peptidase Like Protein 6 (DPP6) Polymorphism on Renal Function via Genome-Wide Typing Association

“…This proved that DPP6 was associated with some neurological diseases, including cognitive diseases and memory impairment [ 41 , 42 , 43 , 44 , 45 , 47 , 51 ]. Some studies also mentioned that exposure to Al would be a potential factor in the development of Alzheimer’s disease, but the causal relationship was still controversial [ 52 , 53 , 54 , 55 ]; however, our finding showed that there was an association between Al in plasma, DPP6 , and eGFR. To our knowledge, there were few studies that explained the indirect effect of DPP6 on eGFR.…”