Objective: To verify the hypothesis that environmental factors acting during the whole lifespan may be involved in the development of Alzheimer’s disease (AD) in late life.
Design: A follow-up study to detect incident AD and dementia, and retrospective assessment of lifetime occupational history.
Materials and Methods: A population-based, dementia-free cohort (n=1301) derived from the Kungsholmen Project, was examined twice during a 6-year long follow-up. A total of 350 dementia cases, including 260 AD patients, were detected. Information on lifetime occupational history, collected from informants, was available for 931 subjects. Occupational-based socioeconomic status (SES) was assessed according to the Swedish Socioeconomic Classification System. Education, major occupation, last occupation, as well as some specific occupational categories and exposures have been examined.
Results: The major findings can be summarized in the following five points.
1) Subjects with elementary schooling had an increased risk of AD, but this association was not explained by occupation-based SES;
2) The combination of low education with either low or high SES was associated with a similar risk of AD, but high-educated subjects with low SES were not at higher risk of AD;
3) Subjects with low occupational SES at 20 years of age, but with high SES at 40 or 60 years of age, had a two-fold increased risk of AD, which disappeared when education was taken into account;
4) Manual workers involved in goods production had an increased risk of AD, even when controlling for education;
5) Among specific exposures, lifetime occupational exposure to extremely-low-frequency magnetic fields (ELF-MFs) was examined. Long-term occupational exposure to ELF-MFs was associated with an increased risk of AD in men, but not in women.
Conclusion: Factors acting early in life are relevant for the development of AD in late life. Manual work and some specific exposures such as ELF-MFs may be associated to an increased risk of AD.
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