The effect of occupation type on risk of Alzheimer's disease in men and women

Abstract

Objectives: To examine the association between the principal lifetime occupation and the incidence of Alzheimer's disease (AD) in men and women in a southern European population aged 55 years or more.

Study design: A community-dwelling sample of 3883 dementia-free individuals aged 55 years or over was classified according the Spanish National Classification of Occupations (CNO-11) and the International Standard Classification of Occupations (ISCO-08) in a four-wave epidemiological study. Medical and psychiatric histories were collected using standardized instruments, including the Mini-Mental Status Examination (MMSE), the History and Aetiology Schedule (HAS), the Geriatric Mental State-AGECAT, and a risk factor Questionnaire. Cases of AD were diagnosed according to DSM-IV criteria. Cox regression models were performed, stratified by sex.

Main outcome measures: Cases of AD according to the main occupation and sex.

Results: In men, compared with the "white collar" category, the risk of AD in "farmers" was 66% times lower, after controlling for potential confounding factors (HR: 0.34; 95% CI: 0.08-1.33). It did not reach statistical significance but the magnitude was large (Cohen's d = 0.84). In women, "farmers" had almost 50% less risk of AD after controlling for all potential confounding factors (HR: 0.55; 95% CI: 0.17-1.78), compared with homemakers, but with a medium effect size (Cohen's d = 0.46).

Conclusions: Men and women farmers had a lower risk of AD, reinforcing the importance of lifetime occupation in the risk of AD at older ages. These results could suggest some environmental hypotheses.

Keywords: Alzheimer’s disease; Epidemiology; Occupation; Risk factor; Sex differences.