Objectives

To estimate the incidence of dementia in a community-dwelling older population from São Paulo city, Brazil.

Methods/Design

This two-phase prospective cohort study evaluated a representative cluster sample of 1370 individuals aged 60 years old and over from three different socioeconomic levels. The community screening phase consisted of a tested combination of cognitive and functional tests administered among the subjects and informants. In the hospital diagnosis phase, the Cambridge Examination was performed; the diagnosis of dementia and dementia subtypes was made according to DSM IV criteria. Incidence rates were expressed in person-years, multiplied by 1000. The risk of developing dementia was calculated using Cox regression.

Results

Among 1370 eligible subjects, 678 were accessed, and 489 completed the evaluation. Forty-two subjects were diagnosed with dementia. The incidence rate of dementia and Alzheimer's disease (AD) were 11.2 (95% CI: 8.0–15.1) and 8.9 (95% CI: 6.1–12.5) per 1000 person-years, respectively; there were high age-specific rates of dementia among younger individuals. There was a trend of a higher risk of developing AD for women than for men. Multivariate analysis showed that older age, the presence of diabetes and the presence of amnestic MCI increased the risk of developing dementia.

Conclusions

The age-specific rates in younger individuals were expressively higher than in worldwide studies and supposedly affected by cardiovascular morbidity. The higher risk in women in a younger sample corroborated the interaction between sex and AD. The increased risk of amnestic MCI reinforced its contribution to the progression to dementia and AD.