Occupational risk factors for Alzheimer disease: a case-control study

Our plain-English summary of Occupational risk factors for Alzheimer disease: a case-control study, by R.T. Gun, A.E. Korten, A.F. Jorm, et al (Alzheimer Disease and Associated Disorders, 1997).

The study

• Authors: R.T. Gun, A.E. Korten, A.F. Jorm, A.S. Henderson, G.A. Broe, H. Creasey, E. McCusker, A. Mylvaganam
• Journal: Alzheimer Disease and Associated Disorders
• Published: 1997;11(1):21-7
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

There is evidence to support the role of a number of environmental factors in Alzheimer disease (AD). This study examines the role of chemical and physical exposures in the occupational environment. The sample included 170 patients with AD and 170 medical-practice-based controls, matched for age and sex, who were assessed for histories of occupational exposures to a range of chemical and physical agents, including hydrocarbon solvents, lead, mercury, organophosphates, aluminum, asbestos and other silicates, vibration, and physical underactivity. Occupational histories were obtained from informants for both patients and controls. Exposure was assessed by a panel of occupational hygienists, blinded to the case or control status of each subject, using the occupational histories and the Job-Exposure Matrix of the U.S. National Institute for Occupational Safety and Health. No statistically significant associations were found between any of the exposures and the occurrence of AD, either in the overall study group or in patients with a family history of AD. The findings suggest the absence of any occupational cause for AD.

In plain English

This case-control study from Sydney, Australia, asked whether jobs involving certain chemical and physical exposures, including asbestos, were linked to Alzheimer disease. It compared 170 patients clinically diagnosed with probable or possible Alzheimer disease at two Sydney hospitals with 170 controls from general practices, matched for age and sex. Interviews took place from 1986 to 1989. Informants, mostly relatives, gave each person's full job history. A panel of three occupational hygienists, who did not know who was a patient, judged each person's likely exposures using these histories and a U.S. NIOSH job-exposure database. None of the exposures showed a statistically significant association with Alzheimer disease. For asbestos the odds ratio was 1.45 (95% confidence interval 0.69 to 3.16). Very few people were judged to have had intense exposure, and none of those cases involved asbestos. The authors concluded that none of the risk estimates suggested a causal link. They noted three limitations. Patients' job histories came only from informants, which could underestimate risk. Their accuracy check used only 39 controls. They could not rule out risks for people carrying the apoE ε4 gene variant.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case-control study, with controls matched for age and sex
• Who was studied: 170 patients with clinically diagnosed Alzheimer disease (83 probable, 87 possible) from two Sydney hospitals, and 170 controls from the same or neighboring general practices matched for sex and age. Each group had 64 men and 106 women. Interviews took place from 1986 to 1989.
• Exposure: Lifetime occupational exposure to a range of agents, including asbestos (fiber type not specified), aluminosilicates, other silicates, silicon, aluminum, lead, mercury, zinc, organophosphates, hydrocarbon solvents, vibration and light physical activity. Exposure was judged by a blinded panel of three occupational hygienists from informant job histories and the U.S. NIOSH Job-Exposure Matrix.
• Main results:
  • For probable or possible exposure, none of the odds ratios for any exposure reached statistical significance, and all were close to unity.
  • For asbestos, the odds ratio for probable or possible occupational exposure was 1.45 (95% confidence interval 0.69 to 3.16), which was not statistically significant.
  • Restricting the analysis to probable exposure only, or to exposures before 1980 or before 1970, gave results that were still nonsignificant and close to unity.
  • Very few people were judged to have had intense exposure. The intense exposures involved hydrocarbons and lead; all other exposures, when present, were at low intensity.
  • Sex, education and family history of Alzheimer disease did not significantly alter the results.
• The authors' conclusion: The authors concluded that none of the occupational risk estimates suggested a causal association with Alzheimer disease, and that the evidence supporting the view that Alzheimer disease is not an occupational disease is plausible.
• Limitations the authors state:
  • Patients' occupational histories could be obtained only from informants, which could produce a significant underestimate of risk.
  • The estimates of reporting error and bias came from a subsample of only 39 controls, so the authors said those conclusions should be treated with caution.
  • The study may have had insufficient power to detect significant odds ratios.
  • The study was carried out before apoE genotype was linked to Alzheimer disease, so the exposures cannot be ruled out as risk factors for people with one or more ε4 alleles.

Topics

Medical terms in this study, explained in our Lexicon: Case-Control Study, Occupational Exposure, Silicate.

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