Trends in Prevalence of Dementia in French Farmers from Two Epidemiological Cohorts.

Objectives: To determine the prevalence of dementia and cognitive impairment in older people across generations.

Design: Two prospective cohort studies (Personnes Agées QUID (PAQUID), Aging Multidisciplinary Investigation (AMI)).

Setting: Baseline data from two subsamples of older farmers in southwestern France.

Participants: PAQUID (n = 595) and AMI (n = 906) participants aged 65 and older living at home at baseline (1988 PAQUID, 2008 AMI).

Measurements: Two methods were used to diagnose dementia: a clinical consensus diagnosis and a computer-assisted taxonomy approach (cognitive impairment with disability (CIWD)) using Mini-Mental State Examination and instrumental activity of daily living scores. Crude and standardized prevalences (using PAQUID age-sex structure) and 95% confidence intervals were calculated, and logistic regression was used to explore confounding.

Results: The prevalence of consensus diagnosis of dementia was higher in AMI in 2008 than in PAQUID in 1988 (12.0% vs 5.7%, P < .001), whereas the reverse was observed for CIWD (14.8% vs 23.8%, P < .001), confirmed by logistic regressions (odds ratio (OR) = 2.50, 95% confidence interval (CI) = 1.52-4.12; OR = 0.60, 95% CI = 0.42-0.87, respectively). Educational level increased and management of vascular risk factors improved over the study period, and health and living conditions improved globally.

Conclusion: These findings suggest global cognitive and functional improvement in old farmers (the prevalence of CIWD decreased by 40% over 20 years) and simultaneously a marked change in the subjective boundary between dementia and nondementia according to clinicians.